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IDescriptionThisblogintroducesthedesignofalithiumbatterybackuppowercontrolboardbasedonLM393,whichissimple,stable,reliable,andlow-cost.Itcandirectlyoutputthemainsvoltagewhenthereismainspower,andcontinuouslymonitorthemainsvoltage.Notonlycanthisdesignautomaticallyturnontheinverterwithin10msafterthemainspowerisoff,butitalsohasapowermanagementfunction:whentheinternallithiumbatteryvoltageislowerthanthesetvalue,itwillautomaticallycharge.ThisVediointroducesHowDoesLM393WorksCatalogIDescriptionIIDesignandWorkingPrinciple2.1Design2.2WorkingPrincipleIIITestIVConclsionOrdering&QuantityIIDesignandWorkingPrincipleThedetailsofLM393basedlithiumbatterybackupcircuitareasfollows:2.1Design2.1.1MainsPowerFailureWhenthereisnomainspowerinput,thecontrolpanelwillturnontheinverterandoutput220VACwithin10msofthemainspowerfailure.2.1.2ChargingManagementFigure1.FunctionDiagramWhenthereismainsinput,thecontrolboardfirstshutsdowntheinverteroutputandswitchestothemainsoutput;thenentersthechargingmanagementstate(duetothefeatureofthelithiumbatteryprotectionboard,theprotectionboardstopschargingafteroverchargeprotection.WhenthebatteryvoltageWhenitdropstotheoverchargerecoveryvalueorbelow,itwillautomaticallyresumecharging.Whenthereismainsinputforalongtime,thelithiumbatterychargerwillberepeatedlycharged,whichwillaffectthelifeofthelithiumbattery).Whenthelithiumbatteryisfullycharged,itwillstopcharging.Whenitdropstoacertainlevel(thisparameterislowerthantheoverchargerecoveryvalueofthelithiumbatteryprotectionboard,thespecificparametervalueisadjustable)andthenresumecharginguntilitisfullycharged,andrepeattheaboveprocess.2.2WorkingPrincipleAccordingtothedesignrequirements,theprincipledesignofthiscontrolboardisdividedintotwoparts:lithiumbatteryvoltagedetectionandcontrol,andmainsvoltagedetectionandcontrol.ThemainvoltagecomparisonpartofthecontrolboardusesthedualvoltagecomparatorintegratedchipLM393.LM393integrates2independentcomparators,itsoperatingpowersupplyvoltagerangeiswide,itcanworkfor2~36Vwhensinglepowerinput,and1~18Vwhendualpowerinput.Inaddition,itscurrentconsumptionissmall,only0.8mA.AndwhatisthepinoutofLM393?WecantakealookatFigure2below:Pins3,5arethenon-invertinginputterminalsofthetwocomparatorsrespectively;Pins2,6aretheinvertinginputterminalsofthetwocomparatorsrespectively;Pins1,7arethecorrespondingoutputterminalsofthetwocomparatorsrespectively.Figure2.LM393PinoutWhenusedasabasiccomparisoncircuit,ifthevoltageatthenon-invertinginputterminalisgreaterthanthevoltageattheinvertinginputterminal,thecorrespondingoutputterminaloutputsahighlevel,andviceversa.Forexample,whenU5U6,U7outputshighlevel;whenU5U6,U7outputslowlevel.2.2.1LithiumBatteryVoltageDetectionandControlLithiumbatteryvoltagedetectioncontrolisshowninFigure3.(1)PowerSupplyThepowersupplyofthecontrolpartistakenfromthelithiumbatteryofthebackuppowersupply,andthevoltageofthecontrolboardis12VDC.Becausethelithiumbatteryinthisdesignis48V,itsvoltagerangeis32Vto54.6V,whichishigherthanthelargeinputvoltagerequiredbythestabilizerblock7812.Therefore,inordertoprotectthevoltageregulatorblock7812,weneedtoconnecta20Vvoltageregulatortubeinseriesattheinputtostepdown.Here,diodeD5actsasreversevoltageprotection(2)VoltageComparisonThepowermanagementadoptsthecomparatorLM393,thesamplingvoltageofthelithiumbatteryisdividedbyresistorsR11andR12,andtheninputtothenon-invertinginputofLM393.Thereferencevoltagedivides12VthroughtheresistorR4andthepotentiometer,andthenenterstheinvertinginputofLM393.WhenthesamplingvoltageU1ishigherthanthereferencevoltageU2,theoutputterminalcorrespondingtoLM393outputsahighlevel,thetransistor9012isturnedoff,therelaydoesnotoperate,andtheinverterstopsworking.WhenthesamplingvoltageU1islowerthanthereferencevoltageU2,theoutputterminalcorrespondingtoLM393outputsalowlevel,thetransistor9012isturnedon,therelayacts,andtheinverteristurnedon.ThereferencevoltagecanbeadjustedaccordingtotheactualparametersthroughthepotentiometerR5.Figure3.LM393LithiumBatteryVoltageDetectionandControl(3)HysteresisComparatorCircuitInasingle-limitcomparator,iftheinputsignalUinhasaslightinterferencenearthethreshold,theoutputvoltagewillproducecorrespondingjitter(fluctuation).Forexample,inthedesignoflithiumbatteryvoltagedetection,ifthesamplingvoltageofthelithiumbatteryfluctuatesnearthetargetvoltage(seeFigure3),thevoltageofU1ishigherthanthevoltageofU2,andtheoutputofthecomparatorshouldoutputahighlevel.However,iftheU1voltageorU2voltagefluctuatesslightlyatthistime,thetransistor9012islikelytobeturnedonandofffrequentlyatthistime,andthecontroloutputwillbeveryunstable.Thenhowtoovercomethisshortcoming?Wecanintroducepositivefeedbackinthedesign(thatis,thewayofhardwaretoachievereturndifference).Ifweneedtofixatrippointatacertainreferencevoltagevalue,wecaninsertanon-linearelement(suchasacrystaldiode)inthepositivefeedbackcircuit.Byusingtheunidirectionalconductivityofthediode(inFigure2,D10diode1N4148),theaboverequirementscanbeachieved.2.2.2MainsVoltageDetectionandControlThedescriptionofthemainsvoltagedetectioncontrolpartisshowninFigure4.(1)PowerSupplyPartThepowersupplypartusesthesamepowersupplyDC12Vasthelithiumbatteryvoltagedetectionandcontrolpart.(2)MainsVoltageDetectionTakingintoaccountthecostofthemainsvoltagedetectionpart,thisdesignabandonsthetraditionaltransformerorvoltagetransformerdetectionmethod,andusestwooptocouplerchipsPC817todetectthemains.PC817isacommonlyusedlinearoptocoupler,whichisoftenusedinfunctionalcircuitsthatrequiremoreprecision.Whenanelectricalsignalisappliedtotheinputend,thelightemitteremitslightandilluminatesthelightreceiver.Thelightreceiveristurnedonafterreceivingthelight,andgeneratesaphotocurrentoutputfromtheoutputend,thusrealizingtheelectricity-optical-electricityconversion.Thisconversionisoftenappliedtovariouscivilindustrialproductssuchasswitchingpowersupplies,UPS,adapters,etc.Figure4.LM393MainsVoltageDetectionandControlTakeAC220Vasanexample.Inordertoprotecttheoptocoupler,weusea1Mresistorinthedesigntolimitthecurrentoftheoptocoupleremitter.TheoptocouplerchipsU1andU2arerespectivelyturnedonundertheactionofalternatingcurrent,andcooperatewiththecapacitorC6toensurethatthevoltageofthenon-invertinginputterminalU3isgreaterthantheinvertinginputterminalU4undertheconditionofnormalmainsinput.Theoptocouplerchipusedinthisdesigncanalsobeusedforelectricalisolationbetweenthecontrolboardandthemains.Whenthereismainspower:LM393snon-invertinginputterminalU3voltageisDC12VInvertinginputterminalU4voltageis9V(R2,R10dividedvoltage)ThecorrespondingoutputterminalishighThetransistor9014isturnedonTherelayoperatesThenormallyclosedpointisopenThereisoutputbetweenmainsvoltageWhenthereisnomainspower:Thevoltageatthenon-invertinginputterminalU3ofLM393isDC0VThevoltageattheinvertinginputterminalU4is9VThecorrespondingoutputterminalislowlevelThetransistor9014iscutoffTherelaydoesnotoperateThenormallyclosedpointisclosedTheinverteroutputs220V.IIITestAftertesting,thiscontrolcircuitmeetsthedesignrequirements:whenthereismainspowersupply,itoutputsmainsvoltage,andautomaticallyconvertstobackuppowersupplywithin10msinthecaseofmainspowerfailure,andhasgoodchargingmanagementfunctions,asshowninFigure5andFigure6.Figure5.LithiumBatteryVoltageDetectionWaveformFigure6.MainsVoltageDetectionWaveformInpracticalapplications,MOStubesandtriacscanalsobeusedtoreplacetherelaysinthevoltagedetectionandcontrolpartofthelithiumbatteryandtherelaysinthemainsvoltagedetectionandcontrolparttoachievethecontroloutput.IVConclsionThiscontrolboardisdesignedaccordingtothecharacteristicsofthelithiumbatterybackuppowersupplythatisgraduallypopularizedatpresent.Ithastheadvantagesofstronganti-interferenceandlowcost,andhasstrongmarketpromotionvalue.Insubsequentdesigns,wecanalsoaddprotectionfunctionssuchasbatteryunder-voltageprotection,short-circuitprotection,overloadprotection,over-voltageprotection,andover-temperatureprotectionaccordingtouserrequirementstocontinuouslyimprovetheproduct.Afterreadingtheblog,haveyoubetterunderstandLM393?Finally,ifyouhaveanyquestionsaboutLM393,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!

IDescriptionThisblogintroducesthedesignofalithiumbatterybackuppowercontrolboardbasedonLM393,whichissimple,stable,reliable,andlow-cost.Itcandirectlyoutputthemainsvoltagewhenthereismainspower,andcontinuouslymonitorthemainsvoltage.Notonlycanthisdesignautomaticallyturnontheinverterwithin10msafterthemainspowerisoff,butitalsohasapowermanagementfunction:whentheinternallithiumbatteryvoltageislowerthanthesetvalue,itwillautomaticallycharge.ThisVediointroducesHowDoesLM393WorksCatalogIDescriptionIIDesignandWorkingPrinciple2.1Design2.2WorkingPrincipleIIITestIVConclsionOrdering&QuantityIIDesignandWorkingPrincipleThedetailsofLM393basedlithiumbatterybackupcircuitareasfollows:2.1Design2.1.1MainsPowerFailureWhenthereisnomainspowerinput,thecontrolpanelwillturnontheinverterandoutput220VACwithin10msofthemainspowerfailure.2.1.2ChargingManagementFigure1.FunctionDiagramWhenthereismainsinput,thecontrolboardfirstshutsdowntheinverteroutputandswitchestothemainsoutput;thenentersthechargingmanagementstate(duetothefeatureofthelithiumbatteryprotectionboard,theprotectionboardstopschargingafteroverchargeprotection.WhenthebatteryvoltageWhenitdropstotheoverchargerecoveryvalueorbelow,itwillautomaticallyresumecharging.Whenthereismainsinputforalongtime,thelithiumbatterychargerwillberepeatedlycharged,whichwillaffectthelifeofthelithiumbattery).Whenthelithiumbatteryisfullycharged,itwillstopcharging.Whenitdropstoacertainlevel(thisparameterislowerthantheoverchargerecoveryvalueofthelithiumbatteryprotectionboard,thespecificparametervalueisadjustable)andthenresumecharginguntilitisfullycharged,andrepeattheaboveprocess.2.2WorkingPrincipleAccordingtothedesignrequirements,theprincipledesignofthiscontrolboardisdividedintotwoparts:lithiumbatteryvoltagedetectionandcontrol,andmainsvoltagedetectionandcontrol.ThemainvoltagecomparisonpartofthecontrolboardusesthedualvoltagecomparatorintegratedchipLM393.LM393integrates2independentcomparators,itsoperatingpowersupplyvoltagerangeiswide,itcanworkfor2~36Vwhensinglepowerinput,and1~18Vwhendualpowerinput.Inaddition,itscurrentconsumptionissmall,only0.8mA.AndwhatisthepinoutofLM393?WecantakealookatFigure2below:Pins3,5arethenon-invertinginputterminalsofthetwocomparatorsrespectively;Pins2,6aretheinvertinginputterminalsofthetwocomparatorsrespectively;Pins1,7arethecorrespondingoutputterminalsofthetwocomparatorsrespectively.Figure2.LM393PinoutWhenusedasabasiccomparisoncircuit,ifthevoltageatthenon-invertinginputterminalisgreaterthanthevoltageattheinvertinginputterminal,thecorrespondingoutputterminaloutputsahighlevel,andviceversa.Forexample,whenU5U6,U7outputshighlevel;whenU5U6,U7outputslowlevel.2.2.1LithiumBatteryVoltageDetectionandControlLithiumbatteryvoltagedetectioncontrolisshowninFigure3.(1)PowerSupplyThepowersupplyofthecontrolpartistakenfromthelithiumbatteryofthebackuppowersupply,andthevoltageofthecontrolboardis12VDC.Becausethelithiumbatteryinthisdesignis48V,itsvoltagerangeis32Vto54.6V,whichishigherthanthelargeinputvoltagerequiredbythestabilizerblock7812.Therefore,inordertoprotectthevoltageregulatorblock7812,weneedtoconnecta20Vvoltageregulatortubeinseriesattheinputtostepdown.Here,diodeD5actsasreversevoltageprotection(2)VoltageComparisonThepowermanagementadoptsthecomparatorLM393,thesamplingvoltageofthelithiumbatteryisdividedbyresistorsR11andR12,andtheninputtothenon-invertinginputofLM393.Thereferencevoltagedivides12VthroughtheresistorR4andthepotentiometer,andthenenterstheinvertinginputofLM393.WhenthesamplingvoltageU1ishigherthanthereferencevoltageU2,theoutputterminalcorrespondingtoLM393outputsahighlevel,thetransistor9012isturnedoff,therelaydoesnotoperate,andtheinverterstopsworking.WhenthesamplingvoltageU1islowerthanthereferencevoltageU2,theoutputterminalcorrespondingtoLM393outputsalowlevel,thetransistor9012isturnedon,therelayacts,andtheinverteristurnedon.ThereferencevoltagecanbeadjustedaccordingtotheactualparametersthroughthepotentiometerR5.Figure3.LM393LithiumBatteryVoltageDetectionandControl(3)HysteresisComparatorCircuitInasingle-limitcomparator,iftheinputsignalUinhasaslightinterferencenearthethreshold,theoutputvoltagewillproducecorrespondingjitter(fluctuation).Forexample,inthedesignoflithiumbatteryvoltagedetection,ifthesamplingvoltageofthelithiumbatteryfluctuatesnearthetargetvoltage(seeFigure3),thevoltageofU1ishigherthanthevoltageofU2,andtheoutputofthecomparatorshouldoutputahighlevel.However,iftheU1voltageorU2voltagefluctuatesslightlyatthistime,thetransistor9012islikelytobeturnedonandofffrequentlyatthistime,andthecontroloutputwillbeveryunstable.Thenhowtoovercomethisshortcoming?Wecanintroducepositivefeedbackinthedesign(thatis,thewayofhardwaretoachievereturndifference).Ifweneedtofixatrippointatacertainreferencevoltagevalue,wecaninsertanon-linearelement(suchasacrystaldiode)inthepositivefeedbackcircuit.Byusingtheunidirectionalconductivityofthediode(inFigure2,D10diode1N4148),theaboverequirementscanbeachieved.2.2.2MainsVoltageDetectionandControlThedescriptionofthemainsvoltagedetectioncontrolpartisshowninFigure4.(1)PowerSupplyPartThepowersupplypartusesthesamepowersupplyDC12Vasthelithiumbatteryvoltagedetectionandcontrolpart.(2)MainsVoltageDetectionTakingintoaccountthecostofthemainsvoltagedetectionpart,thisdesignabandonsthetraditionaltransformerorvoltagetransformerdetectionmethod,andusestwooptocouplerchipsPC817todetectthemains.PC817isacommonlyusedlinearoptocoupler,whichisoftenusedinfunctionalcircuitsthatrequiremoreprecision.Whenanelectricalsignalisappliedtotheinputend,thelightemitteremitslightandilluminatesthelightreceiver.Thelightreceiveristurnedonafterreceivingthelight,andgeneratesaphotocurrentoutputfromtheoutputend,thusrealizingtheelectricity-optical-electricityconversion.Thisconversionisoftenappliedtovariouscivilindustrialproductssuchasswitchingpowersupplies,UPS,adapters,etc.Figure4.LM393MainsVoltageDetectionandControlTakeAC220Vasanexample.Inordertoprotecttheoptocoupler,weusea1Mresistorinthedesigntolimitthecurrentoftheoptocoupleremitter.TheoptocouplerchipsU1andU2arerespectivelyturnedonundertheactionofalternatingcurrent,andcooperatewiththecapacitorC6toensurethatthevoltageofthenon-invertinginputterminalU3isgreaterthantheinvertinginputterminalU4undertheconditionofnormalmainsinput.Theoptocouplerchipusedinthisdesigncanalsobeusedforelectricalisolationbetweenthecontrolboardandthemains.Whenthereismainspower:LM393snon-invertinginputterminalU3voltageisDC12VInvertinginputterminalU4voltageis9V(R2,R10dividedvoltage)ThecorrespondingoutputterminalishighThetransistor9014isturnedonTherelayoperatesThenormallyclosedpointisopenThereisoutputbetweenmainsvoltageWhenthereisnomainspower:Thevoltageatthenon-invertinginputterminalU3ofLM393isDC0VThevoltageattheinvertinginputterminalU4is9VThecorrespondingoutputterminalislowlevelThetransistor9014iscutoffTherelaydoesnotoperateThenormallyclosedpointisclosedTheinverteroutputs220V.IIITestAftertesting,thiscontrolcircuitmeetsthedesignrequirements:whenthereismainspowersupply,itoutputsmainsvoltage,andautomaticallyconvertstobackuppowersupplywithin10msinthecaseofmainspowerfailure,andhasgoodchargingmanagementfunctions,asshowninFigure5andFigure6.Figure5.LithiumBatteryVoltageDetectionWaveformFigure6.MainsVoltageDetectionWaveformInpracticalapplications,MOStubesandtriacscanalsobeusedtoreplacetherelaysinthevoltagedetectionandcontrolpartofthelithiumbatteryandtherelaysinthemainsvoltagedetectionandcontrolparttoachievethecontroloutput.IVConclsionThiscontrolboardisdesignedaccordingtothecharacteristicsofthelithiumbatterybackuppowersupplythatisgraduallypopularizedatpresent.Ithastheadvantagesofstronganti-interferenceandlowcost,andhasstrongmarketpromotionvalue.Insubsequentdesigns,wecanalsoaddprotectionfunctionssuchasbatteryunder-voltageprotection,short-circuitprotection,overloadprotection,over-voltageprotection,andover-temperatureprotectionaccordingtouserrequirementstocontinuouslyimprovetheproduct.Afterreadingtheblog,haveyoubetterunderstandLM393?Finally,ifyouhaveanyquestionsaboutLM393,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!

IIntroductionTheLM393isadualvoltagecomparator.thismeansthatitaccepts2inputsforcomparison.TheoutputloadresistanceofLM393comparatorcanbeconnectedtoanypowersupplyvoltagewithintheallowablepowersupplyvoltagerange,andisnotlimitedbythevoltagevalueoftheVccterminal.ThisoutputcanbeusedasasimpleopencircuittogroundSPS(whentheloadresistorisnotused),thesinkcurrentoftheoutputpartislimitedbythevalueofthedriverandthedevicethatcanbeobtained.Whenthelimitcurrent(16mA)isreached,theoutputtransistorwillexitandtheoutputvoltagewillrisequickly.Inthisblog,wewilldiscuss3waystousetheLM393comparatortobuildcircuits,including:InfraredObstacleAvoidanceModule,Ni-CdBatteryCharger,andPWMModulationCircuit.LM393imagesareforreferenceonly.Figure1.LM393ComparatorCatalogIIntroductionIILM393BasedInfraredObstacleAvoidanceModule2.1ModuleDescription2.2DescriptionofModuleParameters2.3ModuleInterfaceDescriptionIIILM393Ni-CdBatteryChargerIVLM393PWMModulationCircuitOrdering&QuantityIILM393BasedInfraredObstacleAvoidanceModuleFigure2.LM393InfraredObstacleAvoidanceModule2.1ModuleDescriptionThesensormodulehasstrongadaptabilitytoambientlight.Ithasapairofinfraredemittingandreceivingtubes.Thetransmittingtubeemitsinfraredraysofafrequency.Whenitencountersanobstacle(reflectingsurface)inthedetectiondirection,itwillbereflectedbackandreceivedbythereceivingtube.Afterthereceivedinfraredlightisprocessedbythecomparatorcircuit,thegreenindicatorlightwilllightup,andthesignaloutputinterfaceoutputsadigitalsignal(alow-levelsignal).Thedetectiondistancecanbeadjustedbythepotentiometerknob.Theeffectivedistancerangeis2-30cm,andtheoperatingvoltageItis3.3V-5V.Thedetectiondistanceofthesensorcanbeadjustedbyapotentiometer,whichhasthecharacteristicsofsmallinterference,easyassemblyandconvenientuse.Itcanbewidelyusedinmanysituationssuchasrobotobstacleavoidance,obstacleavoidancetrolley,pipelinecountingandblackandwhitelinetracking.2.2DescriptionofModuleParametersWhenthemoduledetectsanobstaclesignalinfront,thegreenindicatoronthecircuitboardlightsup,andtheOUTportcontinuouslyoutputsalow-levelsignal.Thedetectiondistanceofthismoduleis2~30cm,andthedetectionangleis35.Inaddition,thedetectiondistancecanbeadjustedbythepotentiometer:Byadjustingthepotentiometerclockwise,thedetectiondistanceincreases;Byadjustingthepotentiometercounterclockwise,thedetectiondistancedecreases;Thesensorisactiveinfraredreflectiondetection,sothereflectivityandshapeofthetargetisthekeytothedetectiondistance.Amongthem,theblackdetectiondistanceissmallandthewhiteislarge;thedistanceofsmallareasissmall,andthedistanceoflargeareasislarge;TheoutputportOUTofthesensormodulecanbedirectlyconnectedtotheIOportofthesingle-chipmicrocomputer,oritcandirectlydrivea5Vrelay;connectionmode:VCC-VCC;GND-GND;OUT-IO;TheLM393comparatorhasthecharacteristicsofstableoperation;3-5VDCpowersupplycanbeusedtopowerthemodule.Whenthepoweristurnedon,theredpowerindicatorlights;has3mmscrewholesforeasyfixingandinstallation;Circuitboardsize:3.2CM*1.4CM;Themodulehasadjustedthethresholdcomparisonvoltagethroughthepotentiometer.Unlessunderspecialcircumstances,pleasedonotadjustthepotentiometeratwill.2.3ModuleInterfaceDescriptionVCCexternal3.3V-5Vvoltage(canbedirectlyconnectedto5vmicrocontrollerand3.3vmicrocontroller);ConnectGNDexternallytoGND;OUTsmallboarddigitaloutputinterface(0and1);Theworkingcurrentiswithin10ma;BarriersensormoduleasshowninFigure3.Figure3.InfraredReflectiveSensorModuleIIILM393Ni-CdBatteryChargerThecost-effectivenickel-cadmiumbatterychargerformedbyLM393comparatorisshowninFigure4,whichhasthefollowingcharacteristics:Figure4.Nickel-CadmiumBatteryChargerConstantcurrentchargingisinterspersedwithlargecurrentdischarge.Theconstantcurrentchargingcurrentisabout300mA,andthedischargecurrentincreasesasthebatteryvoltageincreases.Whenthebatteryisnearlyfull,thedischargecurrentreaches400mA.Chargefor1.5secondsanddischargefor0.5secondsatintervals.Afterthehighcurrentchargingiscompleted,thereisabout5mAtricklecharging.Thebatteryvoltageisdetectedduringdischarge.Becausethevoltageduringchargingisalwayshigherthanthevoltageduringdischarging.Ifthereisanerrorbetweenthedetectionandtheactualworkingstateofthebatteryduringcharging,thedetectioncanmorereflectthecapacityofthebatterywhendischarging.Thenumberofrechargeablebatteriescanbe1to4.For500mAhnickel-cadmiumbatteries,thechargingtimeisabout2hours,whichcanmeetthegeneralneeds.IVLM393PWMModulationCircuitWeknowthatPWMgenerallyrequiresasawtoothwaveandacontrolvoltagetobecomparedwithacomparatortoobtainaPWMpulse.Thecomparator2ofLM393votagecomparatorwillbeusedasaPWMcomparator,whosenon-invertinginputendisthecontrolvoltageinputend,andtheinvertinginputendisthesawtoothwaveinputend.Theoutputterminal(pin7)isusedastheoutputterminaltosendthePWMdimmingsignaltotheIRNpinoftheIRS2540/1viatheisolationdiodeVD.TheLM393circuitofPWMModulationisshowninFigure5below.Figure5.PWMModulationCircuitThegenerationofthesawtoothwaveisrealizedbythecomparator1ofLM393.IfyoudonotlookatthecapacitorC1,thecomparator1isamultivibratorwithasquarewaveoutput.Inordertoobtainthesawtoothwave,acapacitorC1isconnectedinparallelwiththeCOMendoftheoutputendofthecomparator1.ThisisactuallythechargingprocessoftheoutputterminalsR1andC1ofthecomparator1.Ifthecapacitanceofthiscapacitorislargeenough,butbecausethechargingofC1requiresR1,andthedischargeofC1istheoutputtransistorofthecomparator,thentheriseandfallofthevoltageattheoutputofthecomparatorwillbeasymmetric,whichwillformanoscillatingsawtoothwave.Figure6.OscillatingSawtoothWaveDuetotheVBUSapplicationofthepowersupplyofthecircuitinthefigure,itneedstobesteppeddownwithRS,andthevoltageregulationofVD2andthepowersupplybypasscapacitorsC3andC4arerequired.Afterreadingtheblog,haveyoubetterunderstandLM393?IfyouarealsointerestedinhowtoDIYyoursolartrackingcarbyusingLM393,youmaywishtobrowserighthererightnow!Finally,ifyouhaveanyquestionsaboutLM393,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!IntroductionLM567isahigh-stabilitylow-frequencyintegratedphase-lockedloopdecoder.Duetoitsgoodnoisesuppressionabilityandcenterfrequencystability,itiswidelyusedinthedecodingofvariouscommunicationequipmentandthedemodulationcircuitofAMandFMsignals.LM567Imagesareforreferenceonly.LM567ToneDecoderCatalogIntroductionDocumentsandMediaPinConfigurationandFunctionsBasicParametersFeaturesApplicationsFunctionalBlockDiagramCircuitDiagramECCNUNSPSCProductManufacturerProductRangeOrdering&QuantityDocumentsandMediaComponentDatasheetsLM567(C)PinConfigurationandFunctionsThedatasheetprovidedaboveisforyourreference,sothatyoucanunderstandthephysicaldimensionsofallpackagesinmoredetail.Theconfigurationofall8pinsandthefunctionofeachpinareasfollows:PinConfigurationAndthefunctionofall8pinsandthefunctionofeachpinareasfollows:PinFunctionBasicParametersBrandNameTexasInstrumentsECCNCodeEAR99FactoryLeadTime1WeekHTSCode8542.39.00.01JESD-30CodeR-PDSO-G8JESD-609Codee3Length4.9mmManufacturerTexasInstrumentsManufacturerPartNumberLM567CMX/NOPBMoistureSensitivityLevel1NumberofFunctions1NumberofTerminals8OperatingTemperature-Max70CPackageBodyMaterialPLASTIC/EPOXYPackageCodeSOPPackageDescriptionSOP-8PackageEquivalenceCodeSOP8,.23PackageShapeRECTANGULARPackageStyleSMALLOUTLINEPartLifeCycleCodeActivePartPackageCodeSOICPbfreeCodeYesPeakReflowTemperature260℃PinCount8QualificationStatusNotQualifiedReachComplianceCodeCompliantRiskRank0.62RohsCodeYesSeatedHeight-Max1.75mmSupplyCurrent-Max15mASupplyVoltage-Nom5VSurfaceMountYESTelecomICTypeTONEDECODERCIRCUITTemperatureGradeCOMMERCIALTerminalFinishMatteTin(Sn)TerminalFormGULLWINGTerminalPitch1.27mmTerminalPositionDUALTime@PeakReflowTemperature-Max(s)NOTSPECIFIEDWidth3.91mmFeatures20to1FrequencyRangeWithanExternalResistorLogicCompatibleOutputWith100-mACurrentSinkingCapabilityBandwidthAdjustableFrom0to14%HighRejectionofOutofBandSignalsandNoiseImmunitytoFalseSignalsHighlyStableCenterFrequencyCenterFrequencyAdjustablefrom0.01Hzto500kHzApplicationsTheLM567tonedecoderisadevicecapableofdetectingwhetheraninputsignaliswithinaselectabledetectionrange.Thedevicehasanopencollectortransistoroutput,soanexternalresistorisrequiredtoreachtheappropriatelogiclevels.Whentheinputsignalisinthedetectionband,thedeviceoutputchangestotheLOWstate.TheinternalfreeoperatingfrequencyoftheVCOdefinesthecenterfrequencyofthedetectionband.AnexternalRCfilterisrequiredtoadjustthisfrequency.Thebandwidthinwhichthedevicewilldetectthedesiredfrequencydependsonthecapacityoftheloopfilterterminal.Usuallya1Fcapacitorisconnectedtothispin.LM567isgenerallyusedinthefollowingsituations:TouchToneDecodingPrecisionOscillatorFrequencyMonitoringandControlWideBandFSKDemodulationUltrasonicControlsCarrierCurrentRemoteControlsCommunicationsPagingDecodersFunctionalBlockDiagramCircuitDiagramThefollowingdescribestheclassiccircuitdiagramofthephase-lockedloopLM567usedincarriercommunicationapplications.Therearemanyapplicationsforit,butthethreecircuitsdescribedbelowhaveallbeentestedbypracticeforreferencebythosewholovecarriercommunication.ClassicCircuitDiagram(1)ClassicCircuitDiagram(2)ClassicCircuitDiagram(3)ECCNUNSPSCDescriptionValueECCNCodeEAR99HTSCode8542.39.00.01ProductManufacturerTexasInstrumentsInc.(TI)isanAmericantechnologycompanythatdesignsandmanufacturessemiconductorsandvariousintegratedcircuits,whichitsellstoelectronicsdesignersandmanufacturersglobally.ItsheadquartersareinDallas,Texas,UnitedStates.TIisoneofthetoptensemiconductorcompaniesworldwide,basedonsalesvolume.TexasInstrumentssfocusisondevelopinganalogchipsandembeddedprocessors,whichaccountsformorethan80%oftheirrevenue.TIalsoproducesTIdigitallightprocessing(DLP)technologyandeducationtechnologyproductsincludingcalculators,microcontrollersandmulti-coreprocessors.Todate,TIhasmorethan43,000patentsworldwide.ProductRangeDevicesBoardsDeveloperToolsARMPROCESSORSAUTOMOTIVEPRODUCTSIDENTIFICATIONSECURITYKinetisCortex-MMicrocontrollersIn-VehicleNetworkNFCLPCCortex-MMicrocontrollersMicrocontrollersandProcessorsRFIDAfterreadingtheblog,haveyoubetterunderstandLM567?IfyouarealsointerestedinhowtouseLM567totestthespeedofyourmotorcycle,youmaywishtobrowserighthererightnow!Finally,ifyouhaveanyquestionsaboutLM567,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!

OPA860

IIntroductionLM567isatonedecodingphase-lockedloopintegratedcircuit.Itiscompactindesign,simpleincircuit,andhasawiderangeofapplications.However,ifusingimproperly,itwillbringtroublesindebugging.ThisblogintroducestheworkingprincipleandtipsabouthowtouseLM567tonedecoderforreadersreference.Figure1.LM567ToneDecoderCatalogIIntroductionIILM567InternalStructurePinFunctionIIILM567WorkingPrincipleApplicationIVTipsofUsingToneDecoderLM567Ordering&QuantityIILM567InternalStructurePinFunctionThenameofLM567isphase-lockedlooptonedecoder,itspackageformuses8-pindualin-line,itsinternalstructureandpinfunctionsareillustratedinFigure2.Itsinternalcircuitstructureiscomposedofquadraturephase,detector,phase-lockedloop,amplifier,etc.TheoperatingvoltagerangeofLM567is4.75-9V,theoperatingfrequencycanreach500KHz,andthestaticoperatingcurrentisonly8mA.Thepin③isthesignalinputterminal,whichrequirestheinputsignaltobegreaterthan25mV.Thepin⑧isthelogicoutputterminal.Itcanbeseenfromthefigurethatitisanopencollectortransistoroutput,whichallowsamaximumsinkcurrentof100mA.Theexternalresistanceandcapacitanceofpins⑤and⑥determinethecenterfrequencyf01/1.1RCofICinternalvoltagecontrolledoscillator.Pins①and②areusuallyconnectedtothegroundseparatelytoformanoutputfilternetworkandalooplow-passfilternetwork.Thecapacitorconnectedtopin②determinesthecapturebandwidth.Thelargerthevalueofthecapacitor,thenarrowertheloopbandwidthis.Figure2.TopViewofLM567IIILM567WorkingPrincipleApplicationWhenthetonedecoderLM567works,itsphase-lockedloopinternalcurrent-controlledoscillatorgeneratesanoscillationsignalofacertainfrequencyandphase.Thissignalissenttothequadraturephasedetectortogetherwiththesignalinputatpin③forcomparison.Whenthefrequencyofthesignalfallswithinagivenpassband,thephase-lockedlooplocksthissignal,andatthesametimetheinternaltransistoroftheLM567iscontrolledtobepoweredup,andtheoutputterminaloftheLM567outputslowlevel.The⑤pinofLM567outputstherectangularsignaloftheinternaloscillator,andthe⑥pinoutputsthesawtoothpulse.Thefrequencyofbothisthesameasthecenterfrequencyoftheinternaloscillator.The②pinistheoutputofthephase-lockedloopphasedetector.ThevoltageonisthesignalafterF/Vconversion.Ifthetonesignalisinputtothe②pin,thenthe⑤pinoutputstheFMsquarewavesignalmodulatedbythe②pininputsignal.FromthebasicfunctionofLM567,LM567canbeusedasanoscillator,modulatorordemodulator.Therefore,itcanbeusedasabasicdeviceinthecircuit.TheapplicationofLM567hasthefunctionofdecodingaspecificfrequencyintheinputsignal,anditiswidelyusedincommunication,remotecontrol,measurement,frequencymonitoring,etc.Figure3.LM567ToneDecoderIVTipsofUsingToneDecoderLM567AlthoughLM567hasaverywiderangeofapplications,ifitisnothandledproperlyduringdesignandapplication,itstillfailstoachievetheexpectedresults,andevenbringstroubletothedebuggingoraffectsthereliabilityoftheproduct.Therefore,itshouldbeconsideredfromthefollowingaspectswhenusingit:1.SetOperatingFrequencyandBandwidthofLM567AccuratelyandAppropriatelyWeknowthattheinternaloscillationfrequencyf0ofLM567canbepre-setwithintherangeof0.1KHzto500KHz,anditscorrespondingbandwidthcanalsobedeterminedasrequiredwithinthefieldrangeof7%f0to14%f0.Therefore,afterthedetectedsignalisdetermined,theinternaloscillationfrequencyf0ofLM567shouldbesettocoincidewiththecenterfrequencyofthemeasuredsignal,andthetimingcomponentsRandCconnectedwiththe5and6feetofLM567shouldbeusedwithhighprecision.Amongthem,thesettingofthecenterfrequencycanbedeterminedbytheresistancevalueofthetunerR.Whenadjusting,itisnecessarytopreventRshortcircuitoropencircuit,otherwisetheoutputlevelof⑧pinwillbelowlevelwhetherthereisinputsignalornot.Theexternalcapacitanceofthe②pinofLM567determinesthecapturebandwidth.Thesmallerthecapacity,thewiderthecapturebandwidth.However,thecapacitancecannotbereducedblindlytoincreasethebandwidth,soasnottoreducetheanti-interferenceabilityoreventriggerfalsely,whichaffectsthereliabilityoftheproduct.2.MaketheCenterFrequencyofthePassbandCoincidewiththeCenterFrequencyoftheOscillationAsMuchAsPossibleItshouldbenotedthatthecenterfrequencyofthepassbanddoesnotalwayscoincidewiththecenterfrequencyoftheoscillator,andsometimesitwilldeviateseverely.Thiswillinevitablycauseadecreaseinreliabilityandsensitivity.Therefore,measuresshouldbetakentomakethetwocenterscoincideasmuchaspossible.ThecircuitshowninFigure4canminimizethefrequencyoffsetofthetwocenters.Figure4.CircuitofLM5673.WorkingVoltageofLM567ShouldBeStableThestabilityoftheoperatingvoltageoftheLM567hasafixedresponsetothestabilityofthecenterfrequencyofthetonedecoder.4.AvoidMisoperationWhentheOutputTerminalisPoweredOnLM567outputsalowlevelatthemomentwhenthepoweristurnedon.Therefore,forsomeremotecontrolcircuits,itisnecessarytoaddaCRintegrationdelaycircuittotheoutputendtoavoiderroneousoperationwhenthepoweristurnedon.Thisisespeciallyimportantintheon-offcontrolcircuit.Afterreadingtheblog,haveyoubetterunderstandLM567?Finally,ifyouhaveanyquestionsaboutLM567,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!IIntroductionWhentestingenvironmentalprotection,safety,andeconomicindicatorssuchasnoise,accelerationperformance,maximumspeed,andfuelconsumptionofmotorvehicles,itisnecessarytomeasureandcontrolthevehiclespeed.Mostexistingvehiclespeedmeasurementmethodsuseelectronictimingdevicesorstopwatchestomeasurevehicles.Thetimeittakestotravelafixeddistanceandthenfindtheaveragespeed.Generally,theprocessorandthedisplaypartoftheelectronictimingdevicearebasicallythesame,butthespeedsensorpartisdifferent,andthecharacteristicsofthesensordirectlyaffecttheaccuracyofthemeasurementresult.Atpresent,thecommonlyusedspeedsensorsincludepressuresensitivesensors,COMScamerasandparallellightsources.Theformerhasasimplestructure,butitiscumbersometolay,thesensoriseasilydamaged,andthesensitivityisreducedafterlong-termuse,whichaffectsthemeasurementresults.Thelatterhashighsensitivityandaccuratemeasurement.However,thecostistoohigh,involvesmoreequipment,andhashigherrequirementsfortheplacementofthelightsource.Consideringtheaboveproblems,itisafeasiblemethodtodesignanewinfraredspeedsensorusingLM567.Thesensorissmallinsize,lowincost,simpleinoperation,easytouse,hashighsensitivity,accuracy,stabilityandanti-interferenceability,andissuitableformeasuringtheaveragespeedofavehiclewithinafixeddrivingdistance.Figure1.LM567CatalogIIntroductionIIWorkingPrincipleofTraditionalSpeedMeasuringDevice2.1UsingPressureBeltRoadTester2.2UsingLaserRoadTesterIIIWorkingPrincipleofInfraredSpeedSensorBasedonLM5673.1InternalStructureandFunctionofLM5673.2PrincipleofInfraredSpeedMeasurementBasedonLM567IVConclusionOrdering&QuantityIIWorkingPrincipleofTraditionalSpeedMeasuringDeviceThefollowingusesthemeasurementofmotorcycleaccelerationnoiseasanexample,tointroducetheprinciplesandadvantagesdisadvantagesoftheconventionalspeedmeasuringdevicescurrentlycommonlyused.Figure1isasimplifiedlayoutofmotorcycleaccelerationnoisetest.2.1UsingPressureBeltRoadTesterForthespeedmeasurementmethodusingthepressurebeltroadtester,placethepressurebeltatAA,BB,CC,DDrespectivelyandstickthepressurebelttotheroadsurfacewell.ThedistancebetweenAAandBB,CCandDD(thatis,thespeedmeasurementzone)is1meter,andthepressurebeltandtheroadtesterareconnectedinsequencewithacable.WhenthevehiclepassesthepressurebeltatAA,thepressure-sensitivesensorinthepressurebeltistriggered,andthetriggersignalissenttotheroadtestertostartthetimingofitsinternaltimingdevice;WhenthevehiclepassesBB,atriggersignalisgeneratedagaintostopthetimingdevice.Usingtheinternalprocessoroftheroadtester,thetimetakentopassthedistancebetweenAAandBBisconvertedintovehiclespeedanddisplayedontheLCDscreen.Figure2.LayoutDiagramUsingPressureBeltRoadTesterSimilarly,avehiclespeedvaluecanbemeasuredbetweenCCandDDtomeettherequirementsofnoisemeasurement.Theworkingprincipleofthisspeedmeasurementmethodissimple,buttheequipmentismoretroublesometolay,andthesensoriseasilydamaged.Afterlong-termuse,thesensitivitywillbereduced,whichwillaffectthemeasurementresult.2.2UsingLaserRoadTesterForthespeedmeasurementmethodusingthelaserroadtester,fourparallellaserlightsourcesareplacedatfourpositionsofA,B,C,andD,andfourareplacedatfourpositionsofABCD.CMOScameraforreceivinglasersignals.Thelightsourcecanbeadjustedsothatthelaserlightemittedisalignedwiththecenterofthecamera,andthecameraisconnectedtotheroadtesterinsequence.WhenthevehiclepassesAA,thelightisblocked,andthecamerageneratesatriggersignaltomaketheinternaltimingdeviceoftheroadtesterwork;WhenthevehiclepassesBB,atriggersignalisgeneratedagaintostopthetimingdevice,andtheinternalprocessoroftheroadtesterisusedtoconvertthetimespentthroughthedistancebetweenAAandBBtothevehiclespeedanddisplayitontheLCDscreen.on.Figure3.LayoutDiagramUsingLaserRoadTesterSimilarly,aspeedvaluecanbemeasuredbetweenCCandDD.Thesensitivityandmeasurementaccuracyofthisspeedmeasurementmethodareveryhigh,buttheoperationisextremelyinconvenient.Notonlydoeseachlaserlightsourcerequireanindependentpowersupply,butalsothelasersignalmustbedirectedtothecenterreceivingpointofthecamera,whichplaceshighrequirementsontheplacementofthelightsource,otherwisethesensorwillbedifficulttoworkproperly.IIIWorkingPrincipleofInfraredSpeedSensorBasedonLM567Thisblogusesaphase-lockedloopaudiodecodingchipLM567todesignanewinfraredspeedsensor.Itscircuitdiagramandworkingprincipleareasfollows.3.1InternalStructureandFunctionofLM567LM567isspeciallyusedtodemodulateasingletonefrequencymodulationsignal,anditsoperatingfrequencycanbeashighas500kHz.Itiswidelyusedinindustrialautomaticcontrol,remotecontroltelemetry,securityalarmandotherfields.LM567ismainlycomposedofquadraturephasedetector,phase-lockedloopandamplifier.ItsinternalstructureisshowninFigure2.Pins5and6ofLM567areexternallyconnectedwithtimingresistorsandcapacitorsR,C.RandCdeterminethecenterfrequencyf0ofthephase-lockedloopinternalvoltagecontrolledoscillator,thatis,f0.ResistorRisconnectedbetweenpins5and6,ofwhichpin6isgroundedthroughcapacitorC(Uss).IfRis2~20k,theLM567canextractthetonesignalintherangeof0.01~500kHz.Pins1and2ofLM567arerespectivelyconnectedtothegroundwithacapacitortoformanoutputfilternetworkandaphase-lockedlooplow-passfilternetwork.ThecapacityoftheexternalcapacitorC2onpin2determinesthecapturebandwidthofthephase-lockedloop,anditssizeisBw1070.Uinistheeffectivevalueofthesinewavesignalvoltageinputfrompin3,andrequiresUin25mV,generallybetween100~200mV.TheexternalcapacitorC1ofpin1istheoutputfiltercapacitorofthequadraturephasedetector,anditscapacityismorethantwicethecapacityofthecapacitorC2connectedtopin2,whichshouldsatisfyC12C2.Figure4.TopViewofLM567(1)UsingLM567asFrequencyModulatorPin2isconnectedtotheinputofthelow-passfilterofthephase-lockedloop.Themodulatedsignaladdedfrompin2isfilteredbyalow-passfiltertoremoveout-of-bandnoiseandnoise,andthenaddedtothecenterfrequencyf0ofthevoltage-controlledoscillatorforfrequencymodulation,andthenthepin5outputstheFMsignal.Thecenterfrequencyf0oftheFMsignalisdeterminedbytheparametersoftheRCresistor-capacitornetworkconnectedtopins5and6.WhenLM567isusedasthefrequencymodulationcircuit,onlyitsinternalphase-lockedlooplow-passfilterandvoltage-controlledoscillatorareused.ChangingtheparametervalueoftheRCnetworkcanrealizemodulationtodifferentfrequencies.(2)UsingLM567asFrequencyDemodulatorThemodulatedsignalisinputfrompin3.Whenthecenterfrequencyoftheinputsignalisequaltothecenterfrequencyf0ofthevoltage-controlledoscillatorintheLM567,thelow-passfilter(pin2)oftheloopoutputsthedemodulatedsignal.3.2PrincipleofInfraredSpeedMeasurementBasedonLM567ThecircuitdiagramoftheinfraredspeedsensorbasedonLM567isshowninFigure3.TheinternaloscillatoroftheLM567providesasquarewavesignaltodrivefourLEDstoemitinfraredlight,anditsfrequencyisdeterminedbyR2andC4.Figure5.CircuitDiagramofInfraredSpeedSensorPlacethefoursensorsinthefourpositionsA,B,C,andDinFigure1.Whenthevehiclepassesthesensor,theinfraredraysemittedbytheLEDarereflectedbythevehiclebody.ThephotosensitivetubeQ1receivesthereflectedlight,isamplifiedbythetransistorandconvertedintoavoltagesignal,andissenttotheinternalphasedetectoroftheLM567forsynchronousdemodulation,andthenconvertedintoadigitalsignalbythecomparatorinsidetheLM567andoutputfrompin8.Theoutputsignalistransmittedtotheroadtester,whichtriggersthetimingdeviceintheroadtestertostarttiming.Similarly,whenthevehiclepassesthesensoratpointB,atriggersignalisgeneratedtostopthetimingdeviceandpasstheroadtester.TheinternalprocessoroperatestoobtainthespeedofthevehicleasitpassesAAandBB.LM567isaphase-lockedloopaudiodecodingcircuit.Inthecircuit,itisusedforfrequencyselection,thatis,thecircuitoutputslowlevelonlywhenthefrequencyofthe3-pininputsignalisconsistentwiththefrequencyoftheLM567internaloscillator,otherwisetheoutputishigh.Level.Inotherwords,onlywhenthereflectedinfraredlightreceivedbyQ1comesfromtheLEDinitsowncircuit,theLM567willoutputatriggersignalfromhightolowtotheroadtester.Thebiggestfeatureofthiscircuitistorealizetheautomaticsynchronizationoftheinfraredemissionfrequencyandtheworkingfrequencyofthereceivingcircuit;Thatis,thereisnospecialpulsegeneratingcircuitintheinfraredtransmittingpart,andthepulseisdirectlyintroducedfromthedetectioncircuitofthereceivingpart(LM567phase-lockedcenterfrequencysignal).Inthisway,thewiringanddebuggingworkissimplified,avoidinginconsistenttransmissionandreceptionfrequenciescausedbychangesinthesurroundingenvironmentandcomponentparameters,eliminatingmutualinterferencebetweenadjacentsensors,andgreatlyenhancingcircuitstabilityandanti-interferencecapabilities.IVConclusionTheinfraredspeedsensordesignedbasedontheLM567modulationanddemodulationfunctionrealizestheautomaticsynchronizationoftheinfraredtransmissionfrequencyandtheworkingfrequencyofthereceivingcircuit.Inaddition,ithasthecharacteristicsofstronganti-interferenceabilityandstability,lowcostandsimplestructure.Therefore,itcanbewidelyusedtomeasuretheaveragespeedofvehiclessuchasautomobilesandmotorcycles.Figure6.LM567Afterreadingtheblog,haveyoubetterunderstandLM567?Finally,ifyouhaveanyquestionsaboutLM567,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!TheLM2940isacommonlow-dropout(LDO)linearregulator.ThisisacomprehensiveintroductiontoLM2940voltageregulator,fromitspinout,feature,parametertoitsapplication,itsdifferencebetweenLM7805andmore.CatalogLM2940DescriptionLM2940PinoutLM2940FeaturesLM2940ParametersLM2940EquivalentLM2940VSLM7805LM2940TypicalApplicationLM2940PackageLM2940ApplicationComponentDatasheetLM2940DescriptionTheLM2940isacommonlow-dropout(LDO)linearregulator.Thedropoutvoltageofaregulatoristhevoltagerequiredbetweentheinputandtheregulatedoutputvoltage.Theregulatorwastesthisvoltage(multipliedbycurrent),sothelowerthedropoutonalinearregulator,themoreefficientitis.ThismeansthattheLM2940,witha5Vdropoutat1amp,canbeusedwitha6voltwallwarttoprovidearegulated5Voutput.Thisalsomeansthattheregulatorwilloperateatamuchlowertemperaturethanastandard7805,whichwouldrequireamuchhigherinputvoltage(around7.5volts)foraregulated5Voutput.LM2940PinoutLM2940voltageregulatorLM2940PinoutPinNo.PinNameDescription1VinA(+ve)voltageisgivenasinputtothispin.2GNDCommontobothInputandOutput.3VoutOutputregulated12VistakenatthispinoftheIC.LM2940FeaturesInputVoltageRange=6Vto26VDropoutVoltageTypically0.5VatIOUT=1AOutputCurrentinExcessof1AOutputVoltageTrimmedBeforeAssemblyReverseBatteryProtectionInternalShortCircuitCurrentLimitMirrorImageInsertionProtectionP+ProductEnhancementTestedLM2940ParametersOutputoptionsFixedOutputIout(Max)(A)1Vin(Max)(V)26Vin(Min)(V)6Vout(Max)(V)15Vout(Min)(V)5Fixedoutputoptions(V)5,8,9,10,12,15Noise(uVrms)150Iq(Typ)(mA)10ThermalresistanceJA(C/W)23Loadcapacitance(Min)(F)22RatingCatalogRegulatedoutputs(#)1Features-Accuracy(%)2PSRR@100KHz(dB)48Dropoutvoltage(Vdo)(Typ)(mV)500Operatingtemperaturerange(C)-40to125,-40to85LM2940EquivalentTheequivalentforLM2940isLM7805.LM2940VSLM7805TheLM7805isapopularlinearvoltageregulatorbecauseitrequiresnoadditionalcomponentstooperate.Itisaverylow-costcomponent.Becauseofitscharacteristics,itreducestheoutputvoltageattheexpenseofheatdissipation,makingitinefficient.TheLM7805requiresaminimuminputvoltageof7.3Vtofunctionproperly.Itcanhandleamaximumcurrentof1A.Somemodelscanhandleupto1.5A.Itisrecommended,andinsomecasesrequired,tousecapacitorstoreduceoreliminatetheeffectsofthefrequenciesintroducedbytheotherelementsofthecircuit.Theyalsohelptoreducetheimpactofpeakconsumption.WhiletheLM2940isfromadifferentgeneration,butitspinisstillcompatiblewiththeLM7805.ItisaLow-dropout(LDO)LinearRegulatorthatismoreefficientthantheLM7805,butitwillrequirecapacitors.ThemaindifferencebetweenLM2940andLM7805isthatthemaximumoutputcurrentofLM2940is1A.ThemaximumoutputcurrentofLM7805is1.5A.Othersareveryclose,soifthecircuitonlyrequires1Aorbelow,LM2940canbeusedinsteadofLM7805.Whatsmore,the7805isexpendingtheexcesspowerasheat.Whichisverylossyespecialyifyourprojectusesbatteries.Theotherchipisabuckconverterissoitapproaches90%efficiencybyswitchingsothereisnowasteheat,thatswhyeventhoughLM7805ischeaperandeasiertousebuttheresstillalotofpeoplewouldgoforLM2940.LM2940LM7805SchematicComparisonLM2940SchematicLM7805SchematicLM2940TypicalApplicationLM2940PackageLM2940ApplicationPostregulatorforswitchingsuppliesLogicpowerSuppliesIndustrialInstrumentationComponentDatasheetLM2940Datasheet

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S8050isalow-powerNPNsilicontubewithamaximumcollector-base(Vcbo)voltageof40Vandacollectorcurrent(Ic)of0.5A.S8050isoneofthemostcommonlyusedsemiconductortransistormodelsincircuithardwaredesign.Name:S8050Type:NPNDissipatedpower:0.625W(SMD:0.3W)Collectorcurrent:0.5ABasevoltage:40VCatalogS8050PinoutS8050CircuitS8050ApplicationS8050FeaturesS8050AdvantageS8050AlternativesS8050EquivalentsWhereHowtouseS8050HowtoSafelyLongRunS8050inCircuitS8050PinoutPinNumberPinNameSymbolDescription1EmitterECurrentDrainsoutthroughemitter2BaseBControlsthebiasingoftransistor3CollectorCCurrentflowsinthroughcollectorS8050ApplicationAudioamplificationcircuitsClassBamplifiersPushpulltransistorsCircuitswherehighgainisrequiredLowsignalapplicationsS8050FeaturesLowVoltage,HighCurrentNPNTransistorSmallSignalTransistorMaximumPower:2WattsMaximumDCCurrentGain(hFE)is400ContinuousCollectorcurrent(IC)is700mABase-EmitterVoltage(VBE)is5VCollector-EmitterVoltage(VCE)is20VCollector-BaseVoltage(VCB)is30VHighUsedinpush-pullconfigurationdoeClassBamplifiersAvailableinTo-92PackageNote:CompleteTechnicalDetailscanbefoundattheS8050datasheetgivenattheendofthispage.S8050AdvantageS8050npntransistorS8050isaNPNtransistorhencethecollectorandemitterwillbeleftopen(Reversebiased)whenthebasepinisheldatgroundandwillbeclosed(Forwardbiased)whenasignalisprovidedtobasepin.Ithasamaximumgainvalueof400;thisvaluedeterminestheamplificationcapacityofthetransistornormallyS8050.Sinceitisveryhighitisnormallyusedforamplificationpurposes.However,atanormaloperatingcollectorcurrentthetypicalvalueofgainwillbe110.ThemaximumamountofcurrentthatcouldflowthroughtheCollectorpinis700mA,hencewecannotdriveloadsthatconsumemorethan700mAusingthistransistor.Tobiasatransistorwehavetosupplycurrenttobasepin,thiscurrent(IB)shouldbelimitedto5mA.Whenthistransistorisfullybiasedthenitcanallowamaximumof700mAtoflowacrossthecollectorandemitter.ThisstageiscalledSaturationRegionandthetypicalvoltageallowedacrosstheCollector-Emitter(VCE)orCollector-Base(VCB)couldbe20Vand30Vrespectively.Whenbasecurrentisremovedthetransistorbecomesfullyoff,thisstageiscalledastheCut-offRegion.S8050Alternatives2N3904,2N3906,2N2369,2N3055,S9014,MPSA42,SS8050,BC547S8050Equivalents2N5830,S9013S8050CircuitThisisavideointroducingtransistorsstereoamplifierS8050andS8550.WhereHowtouseS8050S8050transistorisageneral-purposetransistor,itisaperfecttransistortoperformsmallandgeneraltasksinelectroniccircuits.Youcanuseitasaswitchinelectroniccircuitstoswitchonloadsunder700mA.700mAisenoughtohandlevarietyofloadsforexamplerelays,LEDs,bulbsetc.Itcanalsobeusedasamplifierinsmallamplificationstagesorasaseparatesmallsignalamplifier.HowtoSafelyLongRunS8050inCircuitTosafelyrunS8050transistorinyourcircuitorelectronicprojectsdonotoperatethistransistorfromvoltagehigherthan20Vanddonotoperateanyloadmorethan700mAor0.7A.Useasuitablebaseresistorwhichwilllimitsthebasecurrenttoitsrequiredlevel.Donotexposeittoheatover150centigradeandbelow-60Centigrade.LM3914isamonolithicicthatsensesanalogvoltagelevelsanddrives10LEDs,providingalinearanalogdisplay.Asinglepinchangesthedisplayfromamovingdottoabargraph.ThisisanoverviewofLM3914dot/bardisplaydriver,wewillprovidetheinformationofitspinout,datasheet,parameter,andwherehowtousethisdeviceandsomuchmore.Top5electronicsProjectsusingLM3914-15IC|lm3914lm3915circuitsCatalogLM3914DescriptionLM3914PinoutLM3914FeaturesLM3914ParameterLM3914EquivalentWheretouseLM3914ICHowtouseLM3914ICLM3914CircuitLM3914PackageLM3914ApplicationComponentDatasheetLM3914DescriptionTheLM3914isamonolithicintegratedcircuitthatsensesanalogvoltagelevelsanddrives10LEDs,providingalinearanalogdisplay.Asinglepinchangesthedisplayfromamovingdottoabargraph.CurrentdrivetotheLEDsisregulatedandprogrammable,eliminatingtheneedforresistors.Thisfeatureisonethatallowsoperationofthewholesystemfromlessthan3V.TheLM3914isveryeasytoapplyasananalogmetercircuit.A1.2Vfull-scalemeterrequiresonly1resistorandasingle3Vto15Vsupplyinadditiontothe10displayLEDs.Ifthe1resistorisapot,itbecomestheLEDbrightnesscontrol.Thesimplifiedblockdiagramillustratesthisextremelysimpleexternalcircuitry.Wheninthedotmode,thereisasmallamountofoverlaporfade(about1mV)betweensegments.ThisassuresthatatnotimewillallLEDsbeOFF,andthusanyambiguousdisplayisavoided.Variousnoveldisplaysarepossible.TheLM3914isratedforoperationfrom0Cto+70C.TheLM3914N-1isavailableinan18-leadPDIP(NFK)package.LM3914PinoutLM3914LM3914PinoutPinNumberPinNameDescription1and10to18LED1,LED2,LED3.....LED10The10LEDswhichhastobecontrolledisconnectedtothesepins2V-/GroundGroundpinoftheIC3V+/VccSupplyVoltage(3-18)V4RLOLowlevelvoltageforpotentialdivider5SignalAnalogsignalInputpinbasedonwhichtheLEDiscontrolled.6RHIHighLevelvoltageforpotentialdivider7REFOUTOutputReferenceVoltageforLEDcurrentlimiting8REFADJAdjustpinforvoltagereference9ModeSelectbetweenDot/BarModeLM3914FeaturesAnalogControlledLEDDriverICNumberofcontrollableLEDs:10OperatingVoltage:3Vto18VInputAnalogvoltagerange:1.2Vto12VLEDsinkcurrent:2mAto30mA(programmable)BothDot/BarmodeavailableCanbecascadedtocontrolupto100LEDsAvailablein18-pinDIP,PLCCpackageItcandriveLCDs,LEDsotherwisevacuumfluorescents.Thedototherwisebotdisplaymodecanbeselectedbytheuserexternally.Itcanbeexpandableupto100displays.LM3914ParameterManufacturer:TexasInstrumentsSeries:-Packaging:TubePartStatus:ObsoleteDisplayType:LEDLCDVacuumFluorescent(VF)Configuration:Dot/BarDisplayInterface:-DigitsorCharacters:10StepsCurrent-Supply:6.1mAVoltage-Supply:3V~20VOperatingTemperature:0C~70CMountingType:ThroughHolePackage/Case:18-DIP(0.3007.62mm)SupplierDevicePackage:18-PDIPBasePartNumber:LM3914LM3914EquivalentLM3914EquivalentLEDDriver:LM3916AlternativeLEDDriverICs:CD4511,MAX7219,CD4054WheretouseLM3914ICTheLM3914isananalogcontrolledLEDdriverIC,whichmeansthatitcancontrol(turnonoroff)10LEDlightsusingananaloginputvoltage.Thisintegratedcircuiteliminatestheneedforamicrocontrollerandprogramming,aswellasthehardwarerequiredtocontroltenLEDs.Theanaloginputvoltagecanrangefrom3Vto18V,andtheLEDcurrentcanbecontrolledwithasingleresistoronpin7.(RefOut).TheICalsohastwooperatingmodes:DOTmodeandBARmode,andupto100LEDscanbecontrolledbycascadingmultipleICs.TheseICsarecommonlyusedinvisualalarmsandothermetering/monitoringapplicationsbecausetheLEDscanbecontrolledwithoutflickeringandflawlesslywithequalbrightness.So,ifyourelookingforanICtopoweryourbarLEDlightsoranother10-LEDsequence,thisICmightbeofinteresttoyou.HowtouseLM3914ICThebenefitofusingLM3914isthatitrequireslittlehardwareandissimpletosetup.Simplyconnectthe10LEDstotheIC,setthereferencevoltagesfortheinputvoltage,andlimitthecurrentthroughtheLED,andweredone.ThecircuitbelowisanexampleofanLM3914applicationcircuit.SimplyconnecttheV+andV-topowertheIC,andtheanalogsignalvoltageisconnectedtopin5.Inthiscase,weused9VtopowertheICandmonitorananalogyvoltagerangingfrom0to5V.AlwayskeepinmindthatthevoltageusedtopowertheIC(inthiscase,9V)shouldbeatleast1.5Vhigherthanthemonitoringvoltage(here5V).Becausewearemonitoring0-5Vhere,wesetthelowreferencevoltage(pin4)to0Vandthehighreferencevoltage(pin6)to5V.Asyoumayhavenoticed,weconnectedalltenLEDsdirectlytotheICwithoutusinganycurrentlimitingresistors.ThisisbecausetheIChasaninternalcurrentlimiterandthecurrentvaluecanbesetusingthepinVRO(pin7).Thecurrentcalculationformulasaregivenbelow,whereIisthecurrentflowingthrougheachLEDandRListheresistorconnectedtopin7.I=12.5/RLIntheprecedingexample,weuseda470ohmresistorasRl,sothecurrentthrougheachLEDwillbearound25mA;youcanchangethevalueasneeded.Also,thecathodeoftheLEDisconnectedtotheIC,whiletheanodeisconnectedto+5V.ThisisduetothefactthattheICoutputpinscanonlysinkcurrentandnotsourceit.Theintegratedcircuit(IC)canoperateintwomodes:dotmodeandbarmode.Indotmode,themodepin(pin9)mustbeleftfloating;inthismode,basedontheinputvoltage,onlyoneLEDwillbeturnedon.InBarmode,connectthemodepin(pin9)toV+,andtheLEDwillturnonandoffsequentiallybasedontheinputvoltage.Boththemodesareshowninthegiffileabove.LM3914CircuitThecircuitdiagramforICLM3914isshownbelow.Thecircuitcanbeconstructedusingbothbasicelectricalandelectroniccomponents.TheICLM3914isacriticalcomponentofthiscircuit.AnalarmdrivingswitchforoverrangecanbeconnectedtoabartypeLMseriesLEDdrivingdisplaycircuitinthefollowingcircuit.Thiscircuitissuitableforbardisplays.LM3914BasedAlarmDriverCircuitThecircuithereemploysaPNPtransistor,denotedbyQ1.ThistransistorcanbeconnectedbetweentheLEDpositiveandnegativeterminals,andthebaseterminalofthetransistorisconnectedtotheICspin-10todrivetheLED10.Inseries,analarmunitisconnectedtothetransistorscollectorterminal.Normally,Q1transistor,LED10,andthealarmunitareallturnedoff;however,ifLED10isactivated,itpullsQ1transistorthroughresistorR2andthusactivatesthealarmunit,indicatingthattheconditionisoutofrange.Intheabovecircuit,analarmunitgeneratesanacousticalarmsoundusingapiezosirenunit,otherwiseagatedastableswitchunitthatcontinuouslyactivatestheLEDbrightnessbetweenhighandlowlevelsbeneaththeover-rangestate,oracombinationofboth.Ifdesired,theunitcanbeswitchedtoanyoftheLEDdisplays,andthealarmwillsoundifthatoranyotherhighLEDisenergized.LM3914PackageLM3914ApplicationBatteryMeterforRobotMonitoringof12VCarBatteryTesterCircuitforSoilMoistureMonitoringofLeadAcidBatteryChargerChargeMonitoringCircuitforAtmosphericKitchenExhaustFanforControllingTemperatureMeterCircuitforTemperatureDigitalgaugesElectronicdisplaysLow-costmonitordevicesCrudeBatterylevelindicatorsFadebarsComponentDatasheetLM3914Datasheet

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IDescriptionThisblogusestheuniversalintegratedchipTL494toconvertanalogsignalsintoPWM(pulsewidthmodulation)signals.Intheoutputpart,N-channelMOSFETandP-channelMOSFETareusedtoformaswitchingpoweramplifier.CatalogIDescriptionIIIntroduction2.1SwitchingPowerAmplifierOverview2.2TL494IntroductionIIISchemeDesign3.1DutyCycleAdjustmentCircuit3.2InputSignalCompressionCircuit3.3MOSFETDriveCircuit3.4WorkingPrincipleofOutputPartIVExperimentalResultsVConclusionFAQOrdering&QuantityIIIntroduction2.1SwitchingPowerAmplifierOverviewWiththerapiddevelopmentofhigh-speedpowerMOSFETproductiontechnology,theoperatingfrequencyofMOSFETisgettinghigherandhigher,thedrivingmethodisgettingsaferandthepriceisgettinglower.Therefore,alargenumberofswitchingpoweramplifiersappliedtovarioushouseholdappliancesandindustrialalarmshaveappearedonthemarketinrecentyears.Comparedwiththelinearpoweramplifier,althoughthecircuitoftheswitchingpoweramplifierisslightlymorecomplicated.Butitisveryefficientandcanreducethesizeoftheheatsink,evenwithoutusingtheheatsink.Therefore,thevolumeoftheproductcanbegreatlyreduced.2.2TL494IntroductionTL494isaswitchingpowersupplypulsewidthmodulation(PWM)controlchip.Formanyyears,asthecheapestdouble-endedPWMchip,TL494hasbeenwidelyusedindouble-endedtopologiessuchaspush-pullandhalf-bridge.Becauseofitsloweroperatingfrequencyandsingle-endedoutputportcharacteristics.Itisoftenusedwithpowerbipolartransistors(BJT).IfusedwithpowerMOSFET,anexternalcircuitisrequired.TL494worksinawidevoltagerangefrom7Vto40V,withamaximumoperatingfrequencyof200kHz,withtheinternalsawtoothgenerator,PWMgenerator,andlagtimeadjustmentfunctions.IIISchemeDesignFigure1isablockdiagramofaTL494-basedswitchingpoweramplifier.Thekeytothecircuitdesignisthedutycycleadjustmentcircuit,inputsignalcompressioncircuit,andMOSFETdrivecircuit.Figure1.TL494SwitchingPowerAmplifier3.1DutyCycleAdjustmentCircuitThedutycycleisthekeytoimprovingvoltageutilizationduringPWMsignalmodulation.BecauseTL494isanintegratedchipforswitchingpowersupply.Therefore,theminimumlagtimeissetto0.1Vinternally.Themaximumdutycycleisapproximately96%attheoutputofthetransmitterstage.Figure2showstheinputpartandpartofthecircuitforPWMsignalmodulation.Figure2.SignalInputsectionandPWMGeneratorInFigure2,whenC4=1000pFandR4=24k,theoperatingfrequencyisabout78kHz.IfthereisnodutycycleadjustmentcircuitD8,D17,R23,becausethecomparisonpointoftheinternaldelaytimecomparatoris0.1V.Sotheminimumon-timeisabout1.52s,andtheminimumdutycycleisD=1.52/1312%.Therefore,thevoltageutilizationratewilldecreaseduringPWM.IfD8,D17,andR23areused,a0.82VbiasvoltagewillbegeneratedatthepointEofthecapacitorC4forthesawtoothwavegeneration,andthestartingpointofthesawtoothwavewillbeincreasedfrom0Vto0.82V.Therefore,theon-timeisreducedto0.64s,andtheminimumdutycycleisreducedtoD=0.64/134.9%.Thiscansignificantlyimprovethevoltageutilization.Figure3istheoutputwaveformwhenthereisnodutycycleadjustmentcircuit.Figure4istheoutputwaveformwhenthereisadutycycleadjustmentcircuit.Figure3.OutputWaveformwithoutDutyCycleAdjustmentCircuitFigure4.OutputWaveformwithDutyCycleAdjustmentCircuit3.2InputSignalCompressionCircuitBecausetheinputsignalofthealarmhasalargevariationrange,itisnecessarytocompressthesignalwithalargeamplitudeaccordingtoacertainratio.InFigure2,R6,R16,D10,D11constitutetheinputsignalcompressioncircuit,anditskeyistousetheinputcharacteristicsofthediode.Figure5showsitsinputcharacteristics.Amongthem,D10andD11areconnectedinparalleltocompresssignalsinbothpositiveandnegativedirections.Figure5.OutputCharacteristicsofInputSignalCompressionCircuitThecompressionratiodependsonthevaluesofR6andR16.Thelargerthevalue,thelargerthecompressionratio.ByadjustingthevaluesofR6andR16,thechangerangeofthecompressedsignalissetto-0.82V~0.82V.Theamountofchangeis1.64V.WecanseeFigure4,thesawtoothvoltagevariationrangeis0.82V~3.25V.SotheoutputsignalvariationrangeoftheTL494internalerroramplifieris2.43V.ThegainoftheinternalerroramplifierdependsonR7andR20.Byadjustingtheirvalues,whentheamountofchangeofthecompressedsignalis1.64V,theoutputsignalchangerangeoftheinternalerroramplifiercanbesetto2.43V.Sincemostalarmsusetweeters,thebasswithalargeamplitudecanbegreatlyreduced.3.3MOSFETDriveCircuitP-channelMOSFETusesIRF9540.Ithasthecharacteristicsofthemaximumoperatingvoltageof100V,themaximumoperatingcurrentof18A,andsaturationwhenVGSvoltageis5V~15V.N-channelMOSFETusesIRF540.Ithasthecharacteristicsofthemaximumoperatingvoltageof100V,themaximumoperatingcurrentof27A,andsaturationwhenVGSvoltageis5V~15V.ThedrivingtransistorQ3adoptsNPNtypeC8050,andQ7adoptsPNPtypeC8550.Bothofthesetwodrivetransistorshavethecharacteristicsofamaximumoperatingvoltageof30V,amaximumoperatingcurrentof1A,andaVBEof12V.Figure6showstheMOSFETdrivecircuit.Figure6.MOSFETDriveCircuitFigure7showstheMOSFETdrivingprinciplewaveform.WhenthepulsevoltageatpointAislow,thecurrentflowsthroughthereversebiasoftheZenerdiodeD7andthetransistorQ3toformaVGSvoltage,andQHisturnedon.WhenthepulsevoltageatpointAishigh,thecurrentflowsthroughthereversebiasoftheZenerdiodeD9andthetransistorQ7toformaVGSvoltage,andQListurnedon.Inaddition,Figure7alsoshowsdetaileddrivingwaveforms.lWhenthepulsevoltageislow,thevoltageislowerthanVLtomakeQHturnon.lWhenthepulsevoltageishigh,itsvoltageishigherthanVHtomakeQLturnon.IttakesacertainamountoftimetochangefromVLtoVH.Atthistime,QHandQLwillbecutoffatthesametime.Therefore,thepulsechangeprocessisverysafe.Figure7.MOSFETDrivingPrincipleWaveformTheVGSofQHandQLisdeterminedbythefollowingformula:Where:VGSisthedrivingvoltageofMOSFET;VCisthepowersupplyvoltage;VDistheregulatedvoltageofZenertubesD7andD9(usuallythesameZenertubeisused);VBEisthecounterbreakdownvoltageofC8050andC8550.Figure8isthemeasureddrivewaveform.Whenthepulsevoltagechangesfromlowtohigh,thetimeforQHandQLtocutoffatthesametimeisabout100~300ns.Figure8.MeasuredDriveWaveform3.4WorkingPrincipleofOutputPartAsshowninFigure6,theoutputpartconsistsofQH,QLandL3,C8,C5,andC7.TheoutputvoltageistransmittedtotheloadafterfilteringhighfrequencywavesthroughL3andC8.Generally,anelectrolyticcapacitorisusedattheoutputend,butthiscircuitusesC5andC7toformahalfbridge,andthenconnectthemidpointtotheload.Theadvantageofthisconnectionmethodisthatthetwocapacitorsarenotonlythetransmissionpathoftheoutputsignal(thecapacitancevalueistheparallelvalueofthetwocapacitors),butalsohasafilteringeffectonthepowersupply(thecapacitancevalueistheseriesvalueofthetwocapacitorsatthistime),andreducetheinternalpressureofthecapacitorbyhalf.IVExperimentalResultsTable1showsthequiescentcurrentwhentheinputvoltageis35Vandtheoperatingfrequencyis78kHzwhenusingdifferentvoltageregulatordiodes.ItcanbeseenfromTable1:Whenthevoltageregulationvalueofthevoltagestabilizingdiodeis0V,5V,thedistancebetweentheconductionpointsofVLandVHistooclose,andtheconductiontimeistoolong,andthereisalargerstaticcurrent.Althoughthecurrentisrelativelysmallat20V,theMOSFETgeneratessevereheat.AscanbeseenfromTable1,whentheoperatingvoltageis35V,theselectionrangeoftheZenerdiodeis7.5V~15V.VConclusionTheexperimentalresultsshowthatthePWMsignalofTL494isusedforN-channelMOSFETandP-channelMOSFETtoformaswitchingpoweramplifierwithauniquedrivingmodetoovercometheshortcomingsofsimultaneousconductionoftwopowerMOSFETs.Notonlythat,italsohasidealdrivewaveforms,efficiencygreaterthan95%,goodbandwidthandlowprice,whichfullymeetstherequirementsofindustrialalarms.Andunder18Woutputpower,comparedwiththepoweramplifiercomposedofTDA7481,thereisnotmuchdifference,andthereisbasicallynoheatingphenomenon,andtheheatsinkcanberemoved.Ifyouwanttogetmoreoutputpower,youonlyneedtoincreasetheworkingvoltagetomorethan35VandfitaproperZenerdiode.FAQWhatisTL494?TL494isaPWMcontrollerICusedforpowerelectronicscircuits.Itcomprisesofon-chiptwoerroramplifiersanoscillatorwithadjustablefrequencyfeature,anoutputflip-flophavingpulsesteeringcontrol,andanoutputcontrolcircuitwithfeedback.WhatisthedetaileddescriptionofTL494?TheTL494deviceincorporatesallthefunctionsrequiredintheconstructionofapulse-width-modulation(PWM)controlcircuitonasinglechip.Designedprimarilyforpower-supplycontrol,thisdeviceofferstheflexibilitytotailorthepower-supplycontrolcircuitrytoaspecificapplication.TheTL494devicecontainstwoerroramplifiers,anon-chipadjustableoscillator,adead-timecontrol(DTC)comparator,apulse-steeringcontrolflip-flop,a5-V,5%-precisionregulator,andoutput-controlcircuits.Theerroramplifiersexhibitacommon-modevoltagerangefrom0.3VtoVCC2V.Thedead-timecontrolcomparatorhasafixedoffsetthatprovidesapproximately5%deadtime.Theon-chiposcillatorcanbebypassedbyterminatingRTtothereferenceoutputandprovidingasawtoothinputtoCT,oritcandrivethecommoncircuitsinsynchronousmultiple-railpowersupplies.Theuncommittedoutputtransistorsprovideeithercommon-emitteroremitter-followeroutputcapability.TheTL494deviceprovidesforpush-pullorsingle-endedoutputoperation,whichcanbeselectedthroughtheoutput-controlfunction.Thearchitectureofthisdeviceprohibitsthepossibilityofeitheroutputbeingpulsedtwiceduringpush-pulloperation.WhatareTL494productfeatures?CompletePWMPower-ControlCircuitryUncommittedOutputsfor200-mASinkorSourceCurrentOutputControlSelectsSingle-EndedorPush-PullOperationInternalCircuitryProhibitsDoublePulseatEitherOutputVariableDeadTimeProvidesControlOverTotalRangeWhatisPWMIC?TheTL494fixedfrequencyPWMControllercanbeusedforDCtoDCconversionregardlessofbuckorboosttopology....ThisICfeatureanoutputcontrolcircuit,aflipflop,adeadtimecomparator,twodifferenterroramplifiers,a5Vreferencevoltage,anoscillator,andaPWMcomparator.HowdoesPWMICwork?Asitsnamesuggests,pulsewidthmodulationspeedcontrolworksbydrivingthemotorwithaseriesofON-OFFpulsesandvaryingthedutycycle,thefractionoftimethattheoutputvoltageisONcomparedtowhenitisOFF,ofthepulseswhilekeepingthefrequencyconstant.WhichICisbetterforabuckconverter,TL494orUC3843?TheymainlydifferintypeofcontrolTL494=voltagemodecontrol(Oneloopcontrol).whileUC3843usescurrentmodecontrol(Nestedloopcontrol,withainner/fastcurrentloopandanotherouter/slowervoltageloop)Typicallyvoltagemodeareusedinmultipleoutputconverterswithgoodcross-regulation.CurrentmodewhenyouwanttoparallelmultipleconverterstomakeasingleconverterwithhighercurrentratingTL494isaverypopularIC.IfyouhavesimplerequirementsTL494isrecommendedHowdoIproperlysetthefeedbackpinonaTL494SMPSIC?Thefeedbackpinistheoutputofbotherroramplifiers,usedincomparingandadjustingtheoutputpulsewidthtotheDCcontrolvoltage.OnvariouscircuitsIhavelookedup,theop-ampconnectedtopins23areusedtosetthegainofthefeedbackloop,using2resistorswithoneresistorconnectingto2.5Vpotentialdivideron5Vreferencevoltage.Withtheotherconnectingtotheoutput(viasuitableisolation)Thegainappearstobesetat101,usinga51kfeedbackwith510ohmstothe2.5Vreference.Itisusedtocontrolthegainofthefeedbackvoltage.NoliteratureIhaveyetfound,givesanindicationonhowthisgainbeset,exceptagraphshowinganopenloopgainof1000,presumablythegainissetforthebeststability,althoughtherewillalsobeatimeconstant.WhyistherenofrequencycompensationrequiredinTIsTL494examplebuckregulatordesign(operationalamplifier,buckphase,shiftphase,margin,TL494,electronics)?ItsafixedfrequencyPWMcontrollerwithinternaldeadtimetimer.Frequencycompensationisnotrequired.Takealookatthedatasheet.HowtouseTL494?

IDescriptionTL494,isaswitchingpowersupplypulse-widthmodulation(PWM)controlchip.DesignedandintroducedbyTexasInstrumentsintheearly1980s,theTL494gainedimmediateandwidespreadmarketacceptance,especiallyinATXhalf-bridgepowersuppliesforPCcomputers.TL494PWMControllerTL494hasbecomeanindustry-standardchip,producedbymanyintegratedcircuitmanufacturers.Widelyusedinsingle-endedforwarddual-tube,half-bridge,andfull-bridgeswitchingpowersupplies.TL494hastwopackagingforms,SO-16andPDIP-16,tomeettherequirementsofdifferentoccasions.CatalogIDescriptionIITL494FeaturesIIITL494InternalStructure3.15VReferenceSource3.2SawtoothOscillator3.3OperationalAmplifier3.4Comparator3.5PulseTrigger3.6QuietTimeComparatorIVTL494WorkingPrincipleVConclusionFAQOrdering&QuantityIITL494FeaturesCompletePWMPower-ControlCircuitryUncommittedOutputsfor200-mASinkorSourceCurrentOutputControlSelectsSingle-EndedorPush-PullOperationInternalCircuitryProhibitsDoublePulseatEitherOutputVariableDeadTimeProvidesControlOverTotalRangeInternalRegulatorProvidesaStable5-VReferenceSupplyWith5%ToleranceCircuitArchitectureAllowsEasySynchronizationIIITL494InternalStructureFigure1.TL494InternalStructure3.15VReferenceSourceTL494hasabuilt-inreferencesourcebasedonthebandgapprinciple.Thestableoutputvoltageofthereferencesourceis5V.TheconditionisthattheVCCvoltageisabove7V.Theerroriswithin100mV.Theoutputpinofthereferencesourceisthe14thpinREF.3.2SawtoothOscillatorTL494hasabuilt-inlinearsawtoothwaveoscillator,whichgeneratesa0.3~3Vsawtoothwave.TheoscillationfrequencycanbeadjustedbyanexternalresistorRtandacapacitorCt.Itsoscillationfrequencyis:f=1/Rt*CtAmongthem:TheunitofRtisohm;TheunitofCtisfarad.ThesawtoothwavecanbemeasuredattheCtpin.3.3OperationalAmplifierTL494integratestwooperationalamplifierspoweredbyasinglepowersupply.Thetransferfunctionoftheoperationalamplifierisft(ni,inv)=A(ni-inv),butitcannotexceedtheoutputswing.Ingeneralpowercircuits,theop-ampisconnectedtooperateinaclosed-loop.Open-loopisusedinafewspecialcases,andthesignalisinputfromtheoutside.Theoutputterminalsofthetwooperationalamplifiersarerespectivelyconnectedtoadiode,whichisconnectedtotheCOMPpinandthesubsequentcircuit(comparator).Thisensuresthatthehigheroutputofthetwoop-ampsentersthesubsequentcircuit.3.4ComparatorThesignal(COMPpin)outputbytheoperationalamplifierentersthepositiveinputterminalofthecomparatorinsidethechipandiscomparedwiththesawtoothwaveenteringthenegativeinputterminal.WhenthesawtoothwaveishigherthanthesignaloftheCOMPpin,thecomparatoroutputs0,otherwise,itoutputs1.3.5PulseTriggerThepulseflip-flopturnsonatthefallingedgeofthesawtoothwaveandthecomparatoroutputs1.Thismakesoneofthetwooutputs(inturn)on-chiptransistorsareturnedonandcutoffwhenthecomparatoroutputdropstozero.3.6QuietTimeComparatorThedeadzonetimeissetbyDeadTimeControlpin4.Itusesacomparatortointerferewiththepulsetriggerandlimitthemaximumdutycycle.Theupperlimitofthedutycycleofeachendcanbesetupto45%,andtheupperlimitofthedutycycleisabout42%whentheoperatingfrequencyishigherthan150KHz.(WhentheDTCpinlevelissetto0).IVTL494WorkingPrincipleTL494isafixedfrequencypulsewidthmodulationcircuitwithabuilt-inlinearsawtoothoscillator.Theoscillationfrequencycanbeadjustedbyanexternalresistorandacapacitor.Theoscillationfrequencyisasfollows:ThewidthoftheoutputpulseisachievedbycomparingthepositivesawtoothvoltageonthecapacitorCTwiththeothertwocontrolsignals.ThepoweroutputtubesQ1andQ2arecontrolledbyaNORgate.Itwillbestrobedwhentheclocksignaloftheflip-flopislow.Thatis,itwillbegatedonlywhenthesawtoothvoltageisgreaterthanthecontrolsignal.Whenthecontrolsignalincreases,theoutputpulsewidthwilldecrease.Wecantakealookatthepicturebelow.Figure2.TL494PulseControlWaveform​Thecontrolsignalisinputfromtheoutsideoftheintegratedcircuit.Oneissenttothedeadtimecomparator,andoneissenttotheinputoftheerroramplifier.Thedead-timecomparatorhasaninputcompensationvoltageof120mV,whichlimitstheminimumoutputdead-timetoapproximately4%ofthesawtoothperiod.Whentheoutputterminalisgrounded,themaximumoutputdutycycleis96%.Whentheoutputterminalisconnectedtothereferencelevel,thedutycycleis48%.Whenthedeadtimecontrolinputisconnectedtoafixedvoltage(rangebetween0-3.3V),additionaldeadtimecanbegeneratedontheoutputpulse.Thepulsewidthmodulationcomparatorprovidesameansfortheerroramplifiertoadjusttheoutputpulsewidth.Whenthefeedbackvoltagechangesfrom0.5Vto3.5,theoutputpulsewidthdropstozerofromthemaximumon-percentagetimedeterminedbythedeadzone.Thetwoerroramplifiershaveacommonmodeinputrangefrom-0.3Vto(Vcc-2.0),whichmaybedetectedfromtheoutputvoltageandcurrentofthepowersupply.Theoutputoftheerroramplifierisalwaysatahighlevel.ItperformsORoperationwiththeinvertinginputterminalofthepulsewidthmodulator.Itisthiscircuitstructurethattheamplifiercandominatethecontrolloopwithminimaloutput.WhenthecomparatorCTdischarges,apositivepulseappearsattheoutputofthedeadzonecomparator,andtheflip-flopconstrainedbythepulseistimed.AtthesametimestoptheworkoftheoutputtubesQ1andQ2.Iftheoutputcontrolterminalisconnectedtothereferencevoltagesource,themodulatedpulseisalternatelyoutputtothetwooutputtransistors,andtheoutputfrequencyisequaltohalfofthepulseoscillator.Ifitworksinasingle-endedstateandthemaximumdutycycleislessthan50%,theoutputdrivesignalisobtainedfromthetransistorQ1orQ2respectively.Afeedbackwindinganddiodeoftheoutputtransformerprovidefeedbackvoltage.Insingle-endedoperatingmode,whenahigherdrivecurrentoutputisrequired,Q1andQ2canalsobeusedinparallel.Atthistime,theoutputmodecontrolpinneedstobegroundedtoturnofftheflip-flop.Inthisstate,theoutputpulsefrequencywillbeequaltotheoscillatorfrequency.VConclusionThisblogsummarizesthecharacteristics,internalstructureandworkingprincipleofTL494.AlthoughthearchitectureofTL494hasbeenproventobeextremelyexcellentinhistory,itisfacingeliminationinthehigh-endmarketduetoitsoldtechnology,lowfrequency,andlackofnewenergy-savingfeatures.However,itisworthmentioningthatTL494isstillwidelyadoptedinthelow-endandmid-endmarkets.FAQWhatisTL494?TL494isaPWMcontrollerICusedforpowerelectronicscircuits.Itcomprisesofon-chiptwoerroramplifiersanoscillatorwithadjustablefrequencyfeature,anoutputflip-flophavingpulsesteeringcontrol,andanoutputcontrolcircuitwithfeedback.WhatisthedetaileddescriptionofTL494?TheTL494deviceincorporatesallthefunctionsrequiredintheconstructionofapulse-width-modulation(PWM)controlcircuitonasinglechip.Designedprimarilyforpower-supplycontrol,thisdeviceofferstheflexibilitytotailorthepower-supplycontrolcircuitrytoaspecificapplication.TheTL494devicecontainstwoerroramplifiers,anon-chipadjustableoscillator,adead-timecontrol(DTC)comparator,apulse-steeringcontrolflip-flop,a5-V,5%-precisionregulator,andoutput-controlcircuits.Theerroramplifiersexhibitacommon-modevoltagerangefrom0.3VtoVCC2V.Thedead-timecontrolcomparatorhasafixedoffsetthatprovidesapproximately5%deadtime.Theon-chiposcillatorcanbebypassedbyterminatingRTtothereferenceoutputandprovidingasawtoothinputtoCT,oritcandrivethecommoncircuitsinsynchronousmultiple-railpowersupplies.Theuncommittedoutputtransistorsprovideeithercommon-emitteroremitter-followeroutputcapability.TheTL494deviceprovidesforpush-pullorsingle-endedoutputoperation,whichcanbeselectedthroughtheoutput-controlfunction.Thearchitectureofthisdeviceprohibitsthepossibilityofeitheroutputbeingpulsedtwiceduringpush-pulloperation.WhatareTL494productfeatures?CompletePWMPower-ControlCircuitryUncommittedOutputsfor200-mASinkorSourceCurrentOutputControlSelectsSingle-EndedorPush-PullOperationInternalCircuitryProhibitsDoublePulseatEitherOutputVariableDeadTimeProvidesControlOverTotalRangeWhatisPWMIC?TheTL494fixedfrequencyPWMControllercanbeusedforDCtoDCconversionregardlessofbuckorboosttopology....ThisICfeatureanoutputcontrolcircuit,aflipflop,adeadtimecomparator,twodifferenterroramplifiers,a5Vreferencevoltage,anoscillator,andaPWMcomparator.HowdoesPWMICwork?Asitsnamesuggests,pulsewidthmodulationspeedcontrolworksbydrivingthemotorwithaseriesofON-OFFpulsesandvaryingthedutycycle,thefractionoftimethattheoutputvoltageisONcomparedtowhenitisOFF,ofthepulseswhilekeepingthefrequencyconstant.WhichICisbetterforabuckconverter,TL494orUC3843?TheymainlydifferintypeofcontrolTL494=voltagemodecontrol(Oneloopcontrol).whileUC3843usescurrentmodecontrol(Nestedloopcontrol,withainner/fastcurrentloopandanotherouter/slowervoltageloop)Typicallyvoltagemodeareusedinmultipleoutputconverterswithgoodcross-regulation.CurrentmodewhenyouwanttoparallelmultipleconverterstomakeasingleconverterwithhighercurrentratingTL494isaverypopularIC.IfyouhavesimplerequirementsTL494isrecommendedHowdoIproperlysetthefeedbackpinonaTL494SMPSIC?Thefeedbackpinistheoutputofbotherroramplifiers,usedincomparingandadjustingtheoutputpulsewidthtotheDCcontrolvoltage.OnvariouscircuitsIhavelookedup,theop-ampconnectedtopins23areusedtosetthegainofthefeedbackloop,using2resistorswithoneresistorconnectingto2.5Vpotentialdivideron5Vreferencevoltage.Withtheotherconnectingtotheoutput(viasuitableisolation)Thegainappearstobesetat101,usinga51kfeedbackwith510ohmstothe2.5Vreference.Itisusedtocontrolthegainofthefeedbackvoltage.NoliteratureIhaveyetfound,givesanindicationonhowthisgainbeset,exceptagraphshowinganopenloopgainof1000,presumablythegainissetforthebeststability,althoughtherewillalsobeatimeconstant.WhyistherenofrequencycompensationrequiredinTIsTL494examplebuckregulatordesign(operationalamplifier,buckphase,shiftphase,margin,TL494,electronics)?ItsafixedfrequencyPWMcontrollerwithinternaldeadtimetimer.Frequencycompensationisnotrequired.Takealookatthedatasheet.HowtouseTL494?I.DescriptionNowadays,LCD,VFD,LEDandotherdisplaydeviceshavebroughtinfinitecharmtointelligenthouseholdappliances.Atpresent,majorchipmanufacturershaveintroducedvariousdedicateddisplaydriverchips,theyhavebecomethemainstreamofdisplaydrivetechnology.However,thedisplayrequirementsofwhitegoodsarerelativelylow.Basedoncostconsiderations,thisarticleintroducesa74HC164-baseddisplaydrivecircuitdesignscheme,whichnotonlyachievesthesamedisplayeffect,reducescosts,butalsoimprovessystemreliability.74HC164CatalogI.DescriptionII.74HC164AdvantageAnalysisIII.74HC164ChipIntroductionIV.74HC164DisplayDriveCircuitV.74HC164DisplayCircuitDriverVI.ProcedureDescriptionFAQOrdering&QuantityII.74HC164AdvantageAnalysisUndernormalcircumstances,thedisplaycircuitofsmarthomeappliancesiscontrolledbyasingle-chipmicrocomputer,suchasthedisplayedcontentandthedisplaymode.Thesingle-chipmicrocomputerplaysanimportantroleinthecontrolcircuitofsmarthomeappliances.Itsselectionnotonlydeterminestherealizationofthecontrolcircuit,butalsohasagreatinfluenceonthecostofthecontroller.Weusetheserialinputandparalleloutputfunctionsofthe74HC164chiptocarryoutserialcommunicationwiththemicrocontroller,andtheparalleloutputportdirectlydrivesthedisplaydevice.ThissolutioncanexpandtheI/Oportofthesingle-chipmicrocomputerandreducetheresourcerequirementsofthesingle-chipmicrocomputer.Moreover,thechipinstallationmethodisveryflexible,whichcanreducethenumberofconnectingwiresofthedisplaypanel,improvethereliabilityofthesystem,andhasagreatercostadvantage.,Itiswidelyusedinbuttonsanddisplaydrivecircuits.III.74HC164ChipIntroduction74HC164isahigh-speedsilicongateCMOSdevice,whichispincompatiblewithlow-powerSchottkyTTL(LSTTL)devices.74HC164isan8-bitedge-triggeredshiftregister,serialinputdata,andthenparalleloutput.Dataisseriallyinputthroughoneofthetwoinputterminals(DSAorDSB);eitherinputterminalcanbeusedasahigh-levelenableterminaltocontrolthedatainputoftheotherinputterminal.Eitherconnectthetwoinputterminalstogether,orconnecttheunusedinputterminalstoahighlevel,sotheymustnotbeleftfloating.Thepindistributionof74HC164isshownasinFig.1.CompatiblewithTTLlevel,thehighestoperatingclockfrequencyis20MHz,thefan-outfactoris10,thepowerdissipationis500mW,andtheoutputcurrentIo(eachend)is25mA,whichcandirectlydriveLEDdisplaydevices.Figure174hc164pinoutAccordingtothelogicfunctionofthechip,thewaveformdiagramoftheinputandoutputsignalscanbeobtained,asshowninFigure2.TheoutputsignalsQ0~Q7aredelayedbyoneclockcyclerespectively,andcanform8scansignals.Figure274HC164signalwaveformIV.74HC164DisplayDriveCircuitThecircuitshowninFigure3isahybriddisplaycircuitcomposedoftouchswitches,nixietubesandLEDs.Amongthem,16buttons,2nixietubes,and8LEDsareatypical538scanningcircuit.The8pinsofthe74HC164chipQ0~Q7outputcolumnscansignals,andthemicrocontrollerdirectlyprovides5rowsofscansignals.Thesingle-chipmicrocomputerprovidesclockinputanddatainputsignalsfor74HC164tocontrolthedisplaycontent.Thecircuitrequires8pinsofthesingle-chipmicrocomputerintotal,whichsaves6pinresourcescomparedwiththeconventionalscanningcircuitandhascertaincostadvantages.DiodeD2-D23playsanisolationroletopreventthemutualinterferenceof74HC164chippinpotential.Forexample:whenachannelisselected,the74HC164outputpinsQ0~Q6arehighlevel,andQ7islowlevel.Atthistime,ifSW1andSW2arepressedatthesametime,pinQ7andpinQ6areinashort-circuitstate,whichwilldamagethechip.Clockinputpinsanddatainputpinsneedtobeconnectedtoceramiccapacitorstoresisthigh-frequencyinterference,butthecapacitanceshouldnotbetoolargetoavoidexcessivedistortionoftheinputwaveformandmakethecircuitunabletoworknormally.Itisrecommendedtouse100-1000pF.Figure3showsapracticalexampleofthecircuitV.74HC164DisplayCircuitDriverTakethe78K0Sseries8-bitMCUUPD78F9116fromNECCorporationofJapanasanexample,thedriverneedstodetect16,thenumberofkeystobedetected,thedisplaydrive28-segmentdigitaltubes,andthenumberofLEDs16(8expandedonthebasisofthereferencecircuit).Thesingle-chipmicrocomputerdirectlyprovides6linescansignals,andatthesametimeprovidesclockinputanddatainputsignalsfor74HC164tocontrolthedisplaycontent.TheIOportisdefinedasfollows:Eachsubroutinescans2groupsof31keys,andscansallkeyswithin8times.Displayscanchannelnumber0~3,displaytimeofeachchannel(1digitaltubeor1groupofLED)occupies1/4,andtherefreshcycledependsonthefrequencyofsubroutineexecution.Theprogrammustbeexecutedcyclically.Itcanbecalledasaregularsubroutineordirectlyembeddedinthemainprogramfile.Itismoreappropriatetoexecuteitevery1~3mS.Theconfirmationtimeforabuttontobeliftedorpressed(24mS~32mS)--(72ms~96mS),theresponsespeedcanmeetpeoplesoperatinghabits,thedisplayrefreshfrequencyissetto250Hz--83Hz,ifitislowerthan40~50HzFlashing.TheprogramflowchartisshowninFigure4.Figure4ProgramflowchartVI.ProcedureDescription(1)ExternalnameandglobalvariabledeclarationFAQHowdoesthe74HC164transmitdatainthemicrocontrollercircuit?Onepinofthesingle-chipmicrocomputerislikeafaucet,andthedataissentonebyone,thatis,likethewaterfromthefaucet,drippingdropbydrop.The74H164islikeasmallbowlreceivingwater.Itisjustfullafterreceiving8dropsofwater.Atthistime,itissenttothedigitaltube.Thesingle-chipmicrocomputermustsendan8-bit(ormore)data,ifitissentatthesametime,itisaparalleltransmission,ifitisabitbybit,itisaserialtransmission.Thedataofthesingle-chipmicrocomputerissenttothe74HC164bitbybit,whichisserial,andthe74HC164sendsthedatatothedigitaltubeatonce,whichisparallel.So74HC164playsarolefromserialtransmissiontoparalleltransmission.Whatisthedifferencebetween74HC164Dand74HC164NMCU?TheDin74HC164Drepresentsachippackage.TheNin74HC164Nmeansdualin-lineplasticpackaging.Whatisthedifferencebetween74HC164and74LS164,cantheybeusedtogether?74ls164isaTTLcircuit,thepowersupplyvoltageis5V,thehigh-leveloutputcurrentIohis-0.4MA,andthelow-leveloutputcurrentis8MA.74HC164isaCMOScircuit,thepowersupplyvoltageis2V~6V,theoutputdrivecurrentcanreachplusorminus20MA.Ifthepowersupplyvoltageyouuseis5Vandtheoutputdrivecurrentissuitablefor74ls164,theycanbeusedtogether.Whatdevicescan74hc164bereplacedwith?74HC164isaCMOSdevicewithapowersupplyvoltageof2V-6V.Itcanbedirectlyreplacedby74HCT164,40H164.Ifthepowersupplyvoltageis5Vandtheoutputdrivecurrentissmall,itcanalsobereplacedby74164,74LS164,74F164,74ALS164.Whichof74LS164and74HC164hashigherdrivingcapability?74LS164isaTTLdevicewithahigh-leveldrivingcapabilityofabout0.4mAandalow-leveldrivingcapabilityofabout8mA.74HC164isaCMOSdevice,withhigh-levelandlow-leveldrivecapabilityupto20mA.TheabovedatacomesfromDATASHEET.Butgenerallyspeaking,thehigh-leveloutputcapabilityofmanyCMOSdevicesisweak,smallerthanTTL,andthelow-leveldrivecapabilityisstronger.Can74hc164nbeusedtodrivethedigitaltube?Ofcourse,youcanusethe164chiptodrivethenixietube,whichismostlyusedinsituationswheretheIOportresourcesaretightandthedisplaydatarefreshofthenixietubeisslow.Whendesigningthecircuit,multiple164chipsareusedincascade,nomatterhowmanydigitaltubesaredriven,only2IOportsofthesingle-chipmicrocomputerareoccupied.ItcanbesaidthatitisthemostIOport-savingdrivingmethod,anditisstilldrivenstatically,withoutstrobeandbrightnessLowphenomenon.Thedisadvantageisthatmultiple164sareusedincascadeconnection,whichwillcausethesingle-chipmicrocomputertosendalargeamountofdisplaydata(1bytepernixietube)atonetimewhenrefreshingthedisplaydata.Duringthisprocess,thenixietubewillbeallon,althoughthedataissentTheprocessdurationisveryshort,butitstillaffectsthedisplayeffect.Itisrecommendedtoturnoffthedigitaltubewhenrefreshingthedata.

IntroductionLM2596seriesisa3.0Astep-downswitchingregulatorchipproducedbyTexasInstruments(TI).Itcontainsafixedfrequencyoscillator(150KHZ)andareferencevoltageregulator(1.23v),andhasperfectprotectioncircuit,currentlimit,thermalshutdowncircuit,etc.LM2596isacommonvoltageregulatorchip,soitspopularapplicationonthemarketisLM2596buckconvertermodule.ThisvediointroducesLM2596buckconvertermoduleCatalogIntroductionDocumentandMediaLM2596PinConfigurationandFunctionsTypicalApplicationCircuitsBasicParametersHowtousetheLM2596RegulatorCADandCAESymbolsAdvantagesFeaturesApplicationsAlternativeModelsHeatsinkforLM2596ProductManufacturerProductRangeFAQOrdering&QuantityDocumentandMediaDatasheetsLM2596LM2596PinConfigurationandFunctionsThedatasheetoflm2596providedaboveisforyourreference,sothatyoucanunderstandthephysicaldimensionsofallpackagesinmoredetail.Theconfigurationofall5pinsandthefunctionofeachpinareasfollows:Thefunctionofall5pinsofLM324stepdownswitchingregulatorareasfollows:PinNumberPinNameDescription1VINThisisthepositiveinputpoweroftheICswitchingregulator.Theremustbeasuitableinputbypasscapacitoronthispintominimizevoltagetransientsandtosupplytheswitchingcurrentsrequiredbytheregulator.2OutputThispinisaninternalswitch.Thevoltageonthispinisswitchedbetweenapproximately(+VIN-VSAT)andapproximately-0.5V,andthedutycycleisVOUT/VIN.Inordertominimizecouplingwithsensitivecircuits,thecopperareaofthePCBconnectedtothispinmustbekepttoaminimum.3GroundCircuitground4FeedBackSensestheregulatedoutputvoltagetocompletethefeedbackloop5ON/OFFEnablepin,shouldbegroundedfornormaloperationTypicalApplicationCircuitsFixedOutputSeriesBuckRegulatorAdjustableOutputSeriesBuckRegulatorBasicParametersVin(Min)4.5VVin(Max)40VVout(Min)3.3VVout(Max)37VIout(Max)3AIq(Typ)5mASwitchingfrequency(Min)110kHzSwitchingfrequency(Max)173kHzFeaturesEnable,OverCurrentProtectionOperatingtemperaturerange-40℃to125℃RatingCatalogApprox.price1ku|1.8US$Regulatedoutputs1HowtousetheLM2596RegulatorItisquiteeasytouseLM2596,becauseitrequiresveryfewcomponents.Theunregulatedvoltageisprovidedtopin1(Vin)throughthefiltercapacitortoreduceinputnoise.TheON/OFForenablepin(pin5)shouldbegroundedtoenabletheIC.Ifsettohighlevel,ICwillentershutdownmodeandpreventleakagecurrent.Thisfunctionisveryusefulforsavinginputpowerwhenworkingonbattery.Thefeedbackpinisanimportantpinforsettingtheoutputvoltage.Itdetectstheoutputvoltageandadjuststheswitchingfrequencyoftheinternalswitchaccordingtothevalueoftheoutputvoltagetoprovidetherequiredoutputvoltage.Finally,theoutputvoltageisobtainedthroughpin2throughtheLCfilter.Thecompletecircuitdiagramisshownbelow,andyoucanusuallyfindthesecircuitsintheLM2596DCconvertermodule.CADandCAESymbolsPackagePinsDownload(NEB)5ViewoptionsDDPAK/TO-263(KTT)5ViewoptionsTO-220(NDH)5ViewoptionsAdvantagesTheLM2596seriesregulatorisamonolithicintegratedcircuitwithallthefunctionsofastep-downswitchingregulator,capableofdrivinga3Aloadthroughexcellentlineandloadregulation.Thesedevicesprovidefixedoutputvoltagesof3.3V,5V,and12V.Theseregulatorsrequireaminimumnumberofexternalcomponents,areeasytouse,andhaveinternalfrequencycompensationandafixedfrequencyoscillator.TheLM2596seriesoperatesataswitchingfrequencyof150kHzandrequiresfewerfiltercomponentsthanlow-frequencyswitchingregulators.Availableinastandard5-pinTO-220packagewithseveraldifferentleadbendoptions,anda5-pinTO-263surfacemountpackage.Features3.3-V,5-V,12-V,andadjustableoutputversionsAdjustableversionoutputvoltagerange:1.2-Vto37-V4%maximumoverlineandloadconditionsAvailableinTO-220andTO-263packages3.0AoutputloadcurrentInputvoltagerangeupto40VRequiresonlyfourexternalcomponentsExcellentlineandloadregulationspecifications150-kHzFixed-frequencyinternaloscillatorTTLshutdowncapabilityLowpowerstandbymode,IQ,typically80AHighefficiencyUsesreadilyavailablestandardinductorsThermalshutdownandcurrent-limitprotectionApplicationsGridinfrastructureEPOSHometheaterAlternativeModelsLM2576BD9876ACT4523Forhighvoltageinput:HVversioncanbeselected,suchasLM2576HVT,LM2576HVS,thehighestinputvoltagecanreach60V;HeatsinkforLM2596LM2596hastwotypesofpackages:TO-220(T);TO-263(S).Generally,theLM2596intheTO-220(T)packageneedstobeequippedwithaheatsink.Thesizeoftheheatsinkisdeterminedbytheinputvoltage,outputvoltage,loadcurrentandambienttemperature.Thehighertheambienttemperature,thehighertheneedforheatdissipation.TheLM2596intheTO-263(S)packageisasurfacemountcomponenttobesolderedonthePCBboard.CopperandPCBboardcontributetotheheatdissipationofthispackageddevice,suchasfreewheelingdiodesandinductors.ThecopperareaonthePCBforsolderingthispackageddevicemustbeatleast0.4squareinches.Morecopperareawillimprovethethermalcharacteristics,butwhenitislargerthan6squareinches,theimprovementinheatdissipationisverysmall,soventilationinthecaseofuse.ProductManufacturerTexasInstrumentsInc.(TI)isanAmericantechnologycompanythatdesignsandmanufacturessemiconductorsandvariousintegratedcircuits,whichitsellstoelectronicsdesignersandmanufacturersglobally.ItsheadquartersareinDallas,Texas,UnitedStates.TIisoneofthetoptensemiconductorcompaniesworldwide,basedonsalesvolume.TexasInstrumentssfocusisondevelopinganalogchipsandembeddedprocessors,whichaccountsformorethan80%oftheirrevenue.TIalsoproducesTIdigitallightprocessing(DLP)technologyandeducationtechnologyproductsincludingcalculators,microcontrollersandmulti-coreprocessors.Todate,TIhasmorethan43,000patentsworldwide.ProductRangeDevicesBoardsDeveloperToolsARMPROCESSORSAUTOMOTIVEPRODUCTSIDENTIFICATIONSECURITYKinetisCortex-MMicrocontrollersIn-VehicleNetworkNFCLPCCortex-MMicrocontrollersMicrocontrollersandProcessorsRFIDFAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.Afterreadingtheblog,haveyoubetterunderstandLM2596?Finally,ifyouhaveanyquestionsaboutLM2596,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!IDescriptionWhatisLM2596?LM2596isaswitchingvoltageregulatorforstep-downpowermanagementmonolithicintegratedcircuits,capableofoutputting3Adrivecurrent,whilehavinggoodlinearityandloadregulationcharacteristics.ThefixedoutputversionsofLM2596are3.3V,5Vand12V,andtheadjustableversioncanoutputvariousvoltageslessthan37V.Withonlyafewexternalcomponents,wecanusethisvoltageregulator!Moreover,theLM2596switchingfrequencyis150KHz,whichmeansthatcomparedwithlow-frequencyswitchingregulators,wecanusesmallerspecificationsoffiltercomponents.Inaddition,LM2596integratesfrequencycompensationandfixedfrequencygenerator.Thisblogwillintroduce4typicalapplicationcircuitsofLM2596.Figure1.LM2596CatalogIDescriptionIICircuitofLM2596Output3.3V,5VIIICircuitofStep-DownVoltageRegulatorsIVLM2596ApplicationCircuitVLM2596AdjustableCurrentLimitingRegulatorFAQOrdering&QuantityIICircuitofLM2596Output3.3V,5VHaveyounoticedthatinthedesignbelow,allLM2596chipschooseasupplyvoltageof5V,3.3Vor1.8V?Thisisbecause,inthedesignofthewholecontrolsystem,ifthepowersupplysystemistoocomplexandredundant,itwillnotonlycauseelectromagneticinterferencetootherpartsofthecircuit,butalsotheeconomicbenefitisnotgood.Therefore,theselectionof5V,3.3Vor1.8Vsupplyvoltageisbeneficialtotheexperimentaldesign.Whataretheotherbenefits?Inthisway,the24Vvoltagecanbedirectlyconvertedintothedesiredvoltagebyusing3LM2596andsomecapacitors,inductors,diodesandsoon.Thiskindofdesigncircuitisnotonlysimpleandconvenient,butalsoveryeconomical.ThepowersupplycircuitisshowninFigure2.Whenweuseit,wecanchoosethechipsofLM2596+5V,LM2596+3.3VandLM2596+1.8Vaccordingtoourneeds:Toobtaintheconnectionofgraph(a)when+1.8Vand+5V,Toobtaintheconnectionofgraph(b)when+3.3V.Figure2.LM2596CircuitDiagramIIICircuitofStep-DownVoltageRegulatorsWhenyouthinkaooutthevoltageregulatorandstep-downmoduleinthesingle-chipmicrocomputersystem,willyouthinkofcommonchipssuchasLM7805andAMS117?SinceLM7805andAMS117arelowincostandcanbeuseddirectlywithoutexternalexpansionofothercomponents,theyhavebeenwidelyused.ButdontforgetthatLM7805hasafataldisadvantage:highheatgenerationandlowoutputcurrent.Inthemicrocontrollersystem,iftheexternaldevicecurrentisverysmall,thenitsOKtochooseLM7805.However,onceweneedtodrivemoduleswithlargercurrentssuchasrelays,LM7805appearstobepowerless,becausehighheatgenerationmeanspowerloss.Inaddition,iftheinputvoltageofLM7805isabout15V,evenifthecurrentrequiredfortheoutputloadissmall,itsheatgenerationisabout85℃(Ithinkthisshouldbeabletofryanegg),soaheatsinkoracoolingfanmustbeaddedtoit.ThismeansthatcostandPCBlayoutwillbeaffected.TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.Thesedevicesareavailableinfixedoutputvoltagesof3.3V,5V,12V,andanadjustableoutputversion.However,itshouldbenotedthatbecauseLM2596isaswitchingvoltageregulator,itsowncalorificvalueisverysmall.ThismeansthatthewideinputvoltagerangecomparedwiththeLM7805,LM2596needstoaddseveralexternalcomponents.Figure3.LM2596Step-DownVoltageRegulatorsFromtheabovefigure,wecanseethatcomparedwithLM7805,LM2596has4moreexternalcomponents,anditsoutputcurrentcanreach3Aatmost,whichisenoughtodealwithcommonsingle-chipmicrocomputersystems,atthesametime,theinputvoltagerangeiswideandthemaximuminputvoltageis40V.LM2596alsohasanadjustableversion.Iftheadjustableversionisusedtomakea0-30vhigh-currentadjustablepowersupply,itiscompletelyfeasible.Figure4.AdjustableLM2596TheabovefigureisacircuitdiagramofanadjustableversionofLM2596,whichcanoutputaDCvoltageof0-37v,whichismuchbetterthanLM317.IVLM2596ApplicationCircuitLM2596supportsadjustableoutput.Whentheinputis40V,theoutputcanbecontinuouslyadjustedto0~37V.Thetypicalapplicationcircuitisasfollows:Figure5.LM2596ApplicationCircuitNote:Thefeedbackwireshouldbefarawayfromtheinductance,andthethickwireinthecircuitmustbeshort.Herewedbettershielditwithagroundwire.TheresistorsR1andR2thatregulatetheoutputvoltageshouldbeclosetothe4pinsoftheLM2596.VLM2596AdjustableCurrentLimitingRegulatorLM2596doesnothavethefunctionofcurrentlimiting,butinsomeelectronicdesignsandauxiliaryequipment,thereisacertaindemandforthefunctionofcurrentlimiting.Althoughthestandardapplicationcircuitgivenbythemanufacturercannotaccomplishthisfunction,wecanaddafunctioncircuittomakeitrealizethecurrentlimitingfunction.AsshowninFigure6:Figure6.LM2596AdjustableCurrentLimitingRegulatorFAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.

IDescriptionThisbloghasdesignedastep-downDCswitchingpowersupply(itsvoltagecanbeadjustedfrom0V)forneutrontubestorage.ThepowersupplyadoptstheBUCKtopology,andtherail-to-railLMV358operationalamplifiervoltagefeedbackcircuitisdesignedtocooperatewiththeLM2596internalerroramplifiertoovercometheshortcomingsthattheminimumoutputvoltageoftheLM2596step-downchipcannotbelowerthan1.2V,therebytheoutputvoltagecanbeadjustedfrom0V.ThisvideoreviewsanLM2596DCtoDC,adjustable,stepdownregualtorCatalogIDescriptionIIIntroductionIIILM2596BasicCircuitIVDesignofZero-startingPeripheralCircuit4.1VoltageReferenceCircuit4.2VoltageFeedbackCircuitVPowerInductorParameterVIAnalysisofExperimentalResultsVIIConclusionFAQOrdering&QuantityIIIntroductionBeforewestartreadingthisblog,pleasetakeafewsecondstolookatthefollowingtwoquestions:①Whatistheneutrontubestorage?②WhatistherelationshipbetweentheneutrontubestorageandtheDCpowersupplythatrequiresthevoltagecanbeadjustedfrom0V?Figure1.LM2596Whatistheneutrontubestorage?Neutrontubestorageisgenerallycomposedofpowderwithstronghydrogenabsorptioncapacityandheatingwire,usedtostoredeuteriumandtritiumgasfornuclearfusionreaction.Bycontrollingthecurrentoftheheatingwire,theoutgassingvolumeofthereservoirandtheairpressureinthetubeareindirectlycontrolled,therebycontrollingtheneutronyield.Itscoldresistanceofthereservoirisabout3.Whenthepassingcurrentreaches0.35A,thereservoirstartstoreleasedeuteriumandtritiumgas.Theadditionoftheionsourcevoltagewillionizethegasintheionsource,andtheaccelerationhighvoltagewillcausetheionizeddeuterium-tritiumionsintheionsourcetobeextractedandaccelerated,andadeuterium-tritiumfusionreactionoccursonthetargettoproduceneutrons.WhatistherelationshipbetweentheneutrontubestorageandtheDCpowersupplythatrequiresthevoltagecanbeadjustedfrom0V?Inordertoaccuratelycontroltheheatingcurrentofthestorage,thepowersupplyoftheneutrontubestoragerequiresthatthevoltagecanbeadjustedfrom0V.Afterwetookaquicklookatoneofthecircuitprotagonists,neutrontubestorage,discussedinthisblog,letstakealookatanotherequallyimportantrole:theLM2596chip.ThevoltagereferenceoftheLM2596integratedvoltageerroramplifieris1.2V,sothatitslowestoutputvoltageisnotlessthan1.2V.ItseemsthattheLM2596chipitselfcannotbeadjustedfrom0V?Howcanthisdefectberesolved?Wecanusetherail-to-railopampLMV358poweredbyasinglepowersupplytodesignthevoltagefeedbackcircuit.Byisolatingthesamplingterminalandthefeedbackterminal,thelinearadjustmentintervaloftheopampcanbeusedtocompensateforthevariationofthefeedbackvoltage,whichcansolvetheproblemofthelowestoutputofLM2596thatcannotbelowerthantheproblemcausedby1.2V.Afterexperimentaltests,thedesignofthepowersupplyfeedbackcircuitissimpleandefficient.Notonlythepoweroutputvoltagecanbeadjustedfromzero,butalsotheoutputvoltageadjustmentaccuracyishigh,sotheactualapplicationneedscanalsosolved.IIILM2596BasicCircuitLM2596isavailableinfixedandadjustableversions.Amongthem,theoutputvoltageoftheadjustableversionrangesfrom1.2vto37V,withthemaximuminputvoltagedoesnotexceed45V.Underloadconditions,thecircuitshowsthefollowingcharacteristics:Voltageregulation4%.Donotneedtoomanycomponentsforperipheralcircuits.Lowpowerbypassmode.Thetypicalstaticcurrentis80A.LM2596minimumoutputvoltage1.2VapplicationcircuitisshowninFigure2.AscanbeseenfromFigure1,thefeedbackresistorsR1andR2determinethevoltagedividerratioofthepowersupplyoutputvoltage,whichcanbeadjustedthroughadjustingR1.WhenR1isadjustedto0,theoutputvoltageistheminimum,whichistheinternalvoltagereferenceoftheLM2596chip.Figure2.LM2596BasicCircuitTheinternalvoltagereferenceatthefeedbackendoftheLM2596chipis1.2V,whichlimitstheoutputvoltageofthepowersupplytobeadjustedfromzero.IVDesignofZero-startingPeripheralCircuitFirst,trytoconnecttheFBterminalandtheVsterminalinFigure1,andadjusttheR1resistanceto0.Atthistime,theVoutisatleast1.2V.Whatshouldwedotoachievethepurposeofadjustingfromzero?WecandisconnectVs,designanindependentvoltagefeedbackcircuittoadjusttheFBterminalvoltage,andchangetheerrorvariationoftheLM2596internalvoltageerroramplifierthroughtheexternalinputvoltagetoincreaseordecreasethePWMoutputdutycycle,whichinturnenablestheoutputvoltagetobeadjustedfromzero.4.1VoltageReferenceCircuitSo,howtoensurethattheFBterminalvoltageofU1isaround1.2V?Sincethesamplingvoltagefeedbackterminalneedsavoltageregulatorforcompensation,wecanuseasimplifiedcircuitdesignmethod,thatis,usingTL431toachievethisgoal.WhatisTL431?TL431hasthefollowingcharacteristics:TL431isatypicalthree-terminalprecisionvoltageregulatorTheoutputvoltagefrom2.5to36Vcanbearbitrarilysetwith2resistorsItsdynamicimpedanceis0.2Theaccuracyofthevoltagereferenceis0.6%ThevoltagereferencecircuitbasedonTL431isshowninFigure3.Figure3.TL431VoltageReferenceCircuitInthiscircuit,thevoltagereferencehavetwofunctions:itcanbothbeusedastheexternalinputvoltagereferenceandthecompensationvoltageofopampinphase.Theexternalinputvoltageisusedtochangetheoutputvoltage,whilethecompensationvoltageisusedtocompensateforthechangeinvoltageatthefeedbackterminal.4.2VoltageFeedbackCircuitThenon-invertingendofU1sinternalvoltageerroramplifierisintegratedwitha1.2VvoltagereferenceandtheoutputvoltagefeedbackresistorR2isconnectedtotheinvertingendoftheerroramplifier:Whenthevoltageatthefeedbackterminalisgreaterthan1.2V,theerroramplifiergeneratesanegativeerrorsignal,thePWMoutputdutycycledecreases,andtheoutputvoltagedecreases;Whenthevoltageatthefeedbackterminalislessthan1.2V,theerroramplifiergeneratesapositiveerrorsignal,thePWMoutputdutycycleincreases,andtheoutputvoltageincreases.Regardlessofwhethertheoutputvoltageofthepowersupplybecomeslargerorsmaller,thechipcankeeptheoutputvoltagestablebycontrollingtheontimeoftheswitchtube,buttheminimumoutputvoltageis1.2V.ThevoltagefeedbackcircuitdesignedbyLMV358isshowninFigure4.Figure4.LMV358VoltageFeedbackCircuitHereisaquestion:Whatisthekeytorealizetheoutputvoltageadjustmentfromzero?Infact,itisverysimple.ThekeyiswhetherthelowestvoltageofFBintheoperationalamplifierfeedbackcircuitcanbe0V.Inthecaseofasinglepowersupply,theopamphasintegratedtransistors,anditsminimumoutputvoltageisabout0.6V(whichobviouslydoesnotmeettheaboverequirements).Ifwewanttosolvethisproblem,wecanchooseLMV358opamppoweredbyrail-to-railsinglepowersupply,withaminimumoutputvoltageof65mV,soastomeettherequirementofpoweradjustmentfromzero.make:M=R14/R13N=R16/(R16+R18)Q=R19/R20Thenthevoltagefeedbackcircuitparametersarecalculatedasfollows:(1)Vo1=Vs(2)Vo2=(1+M)Vref-VadM(3)Vo3=N(Vo1+Vo2)(1+Q)(4)Vo4=kVo3=VfbIntheaboveformula:kisavariablecoefficient.LetFB=1.2V.Whenthepowerisinitiallypoweredon,Vad=0V,Vref=2.5V,buttheoutputvoltageoftheoperationalamplifierdoesnotnecessarilymeetFB=1.2V,causingLM2596tomalfunction.Inordertoavoidthissituation,wecanuseR21tocorrectthevoltagevalueofVfbattheinitialpower-on,sothatFB=1.2V.IncreasetheVadterminalvoltage,theVo2terminalvoltagedecreasesandtheoutputvoltageincreases,sothatVo1increases.Conversely,Vo2compensatesthevariationofVo1toensurethatthevoltageatthefeedbackterminalofthechipisequalto1.2V,sothatthesamplingvoltageVsfollowsthechangeoftheVadvoltage,andthepowersupplycanbeadjustedfromzero.ThetestdataofthevoltagefeedbackcircuitisshowninTable1.Table1.TestDataFromtheabovetestdata,wecanseethatwecanmakeuseofthelinearoutputcharacteristicsoftheoperationalamplifiertoachievethepurposeoflinearadjustmentoftheoutputvoltage.TheVschangeswiththeVad,thechipreferenceterminalvoltageVfbremainsunchanged,andtheoutputvoltagerangeisdeterminedbytheresistancepartialvoltageratio.Undertheconditionoffullload,whentheVadinputvoltagechangesfrom0to5V,thesamplingresistorVsterminalvoltageoutputrangecanbe0to5V,andthepowersupplyoutputvoltageisadjustablefrom0to35Vthroughtheresistordividerratio.VPowerInductorParameterThereare3operatingmodesfortheinductorcurrentintheBUCKcircuit.ThisblogdesignstheinductoraccordingtotheCCMworkingstate,andfine-tunestheinductorparametersaccordingtotheactualtestresults.Whenthepowertubeisturnedon,theinductorcurrentriseslinearly,andthecurrentincrementexpressionis:(5)ION=(VONTON)/LVON,TON,andLaretheinductorconductionvoltage,turn-ontimeandinductance,respectively.Thecurrentdecrementintheturn-offphaseofthepowertubecanbeexpressedas:(6)IOFF=(VOFFTOFF)/LVOFFandTOFFaretheinductorvoltageandturn-offtimewhenturn-off.Inaswitchingcycle,theincrementanddecrementoftheinductorcurrentareequal,andthevolt-secondlawcanbeusedtoobtain:(7)VONTON=VOFFTOFFInthebucktopology,VON=VIN-VO,VOFF=VO,theaboveformulaistransformedtoderivethedutycycleequationofBUCKtopologywork:(8)D=VO/VINHowtodeterminethedutycycle?Thepowersupplyinputvoltageisafixedvalueof40V,andtheoutputvoltagerangeis0-35V.Fromthis,thedutycycleD=0-0.875canbecalculated.Here,wedesigntheinductorparametersaccordingtotheprincipleofmaximumdutycycleandmaximumoutputpower.SohowisILdetermined?ThemaximumloadcapacityofLM2596is3A.FortheBUCKtopology,theaverageinductorcurrentILisequaltotheloadcurrentIO.Wecansetthecurrentrippleratertobe0.3,andthechoiceofraffectsdeviceselectionandcircuitcost.Theexpressionofrisdefinedasfollows:(9)r=I/ILIntheaboveformula:Iisthechangeoftheinductorcurrentinaperiod,andtheparametersaresubstitutedintotheaboveformulatoobtainI=0.9A.Accordingtothelawofelectromagneticinduction,theinductanceiscalculatedasthefollowingformula:(10)L=(VOND)/(rILf)ItisknownthattheswitchingfrequencyoftheLM2596chipis150kHz,andthecalculatedparametersaresubstitutedintotheaboveformulatocalculateL=259H.Intheactualdebugging,thetheoreticallycalculatedinductanceparameterscannotmeetthepracticalapplicationrequirements.Accordingtotheactualdebuggingresults,thehighfrequencypowerinductorwithratedinputcurrent4Aandinductancevalue330Hisselected.VIAnalysisofExperimentalResultsMakeaprototypeaccordingtothedesignparameters.Undertheconditionoffullload,given40Vinputvoltage,theoutputvoltageofthepowersupplyunderdifferentinputvoltageismeasuredbyadjustingtheexternalVadvoltage.Table2showstheoutputvoltagetestdataatload10.1.Inpracticalapplication,theefficiencyofpowersupplyisthefirstconcern.Table3showsthedataformeasuringvoltageandcurrentattheinputandoutputofthepowersupply,respectively.Ascanbeseenfromtables2and3,theinputandoutputvoltagesareproportionaltoeachother,andtheregulationaccuracyoftheoutputvoltageisabout0.05V.Theoutputvoltageofthepowersupplycanbeadjustedfromzero,whichsolvesthedeficiencyof1.2VofthelowestoutputvoltageoftheLM2596chip.Usingtheabovecalculationmethod,theaverageefficiencyofthepowersupplyis93.44%.Usingthetestdataunderno-loadandfull-loadconditions,itiscalculatedthattheloadadjustmentrateofthepowersupplyat35Voutputis1.3%.Inaddition,thepowersupplycannotonlyworkforalongtime,thetemperatureriseisnormal,butalsotheperformanceisstable.Table2.TestData:LM2596DCRegulatedPowerSupply(10.1)Table3.TestData:LM2596DCRegulatedPowerSupplyEfficiencyVIIConclusionInordertosolvetheshortcomingthattheoutputvoltageofLM2596cannotbeadjustedfromzero,thisblogadoptsthemethodofisolatingthesamplingvoltageandthefeedbackendofthechiperroramplifier,thatis:avoltagefeedbackcircuitbydesigningarail-to-railopamptomaketheoutputvoltagecapableofadjustingfromzero.Inaddition,weanalyzedthedesignoftheinductanceparametersoftheadjustableBUCKpowersupplyinprinciple,andmakeaprototypeaccordingtotheparameterstoverifythecorrectnessandreliabilityofthedesign.Theexperimentalresultsshowthattheloadadjustmentrateofthepowersupplyis0.88%,themaximumworkingefficiencyunderratedloadis95.08%,andthefullloadpoweris105W,whichcanmeettheneedsofpracticalapplications.FAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.IDescriptionTheswitchingpowersupplychipLM2596iscompact,low-cost,low-power,high-efficiencyandeasytousecomparedwithspecializedinstruments.ThepowersupplydescribedinthisblogisasteplessadjustableDCregulatedvoltagesupplybasedontheswitchingpowersupplychipLM2596.Figure1.LM2596CatalogIDescriptionIILM2596CircuitandDesignProcess2.1CircuitofSteplessAdjustableDCPowerSupply2.2DesignProcessofAdjustableDCVoltageSourceIIIHowtoApplyandUseLM2596SteplessAdjustableDCPowerSupply3.1HowtoApply?3.2HowtoUse?FAQOrdering&QuantityIILM2596CircuitandDesignProcess2.1CircuitofSteplessAdjustableDCPowerSupplyThispowersupplycircuitmainlyusesLM2596-ADJ.LM2596-ADJisastep-downswitchingpowersupplychip.Itsoutputvoltagerangeis1.2V-37V,anditsmaximumloadcurrentis3A,withexcellentlinearityandloadregulationcharacteristics.Only4externalcomponentsareneededinthemaincircuittoadjusttheoutputvoltage.TheLM2596-ADJchipintegratesfrequencycompensationandafixedfrequencygenerator,andtheswitchingfrequencyis150KHz,whichfacilitatestheuseofsmallerfiltercomponents,therebyreducingvolume,weight,lossandcost.Undercertaininputvoltageandoutputloadconditions,theoutputvoltageerroriswithin4%,theoscillationfrequencyerrorrangeiswithin15%,andthestandbycurrentcanbeonly80uA.Itcanrealizeexternalpower-offandhasaself-protectioncircuit(atwo-stagefrequencyreductioncurrent-limitingprotectioncircuitandanover-temperaturecompleteprotectioncircuitthatiscutoffinabnormalcases).TheLM2596-ADJpackageinthisarticleisTO220(T),whichrequiresanexternalheatsink.VOUT=1.23V*(1+R2/R1)WhendesigningthePCBboard,theexternalcomponentsshouldbeascloseaspossibletotheLM2596-ADJ,andusegroundwireshieldingorsingle-pointgrounding,andusemagneticshieldinginductors.Iftheinductorcoreusedisopen,andtheinductancefluxcrossesthesensitivefeedbackline,thegroundlineoftheintegratedchipandtheconnectionoftheoutputcapacitorCOUTmayhaveproblems.ThefeedbackresistorshouldbeclosetotheLM2596-ADJIC,andtherelatedwiringshouldbefarawayfromtheinductor.Figure2.AdjustableDCVoltageSourceCircuit2.2DesignProcessofAdjustableDCVoltageSourceVOUTistheadjustableoutputvoltageVIN(max)isthemaximumDCinputvoltage,ILOAD(max)isthemaximumloadcurrent,F=switchingfrequency(150KHz)1)OutputVoltageCalculationVOUT=VREF*(1+R2/R1)Amongthem,VREF=1.23V.Inthisblog,R1isa1Kmetalfilmresistorwithalowertemperaturecoefficientof1%accuracy;R2usesa30Kpotentiometer.2)InductorSelectionCalculatetheproductE*Toftheinductorvoltageandmicrosecondsbythefollowingformula:E*T=(VIN-VOUT-VSAT)*(VOUT+VD)/(VIN-VSAT+VD)*1000/150KHz(VuS)VSATistheinternalsaturationvoltageoftheswitch,VSAT=1.16VVDistheforwardvoltagedropofthediodeVD=0.5VUsetheE*TvalueintheformulatofindthematchinginductornumberfromtheordinateinFigure3,andselectthemaximumloadcurrentofthecircuitontheabscissa;determineaninductanceareabytheintersectionoftheE*Tvalue,andthemaximumloadcurrent,andeachareaiscorrespondingtoaninductancevalueandaninductanceserialnumber(LXX).SelecttheappropriateinductorfromthecomponentnumberofthemanufacturerlistedinTable1forLM2596-ADJcircuit,preferablyamagneticshieldinductor.Thisblogchooses68uHinductance.Figure3.LM2596-ADJApplicationInformation3)OutputCapacitorCOUTNumber/Inductance(H)/Current(A)SchottRencoPulseEngineeringCoilcraftIn-LineSurfaceMountIn-LineSurfaceMountIn-LineSurfaceMountSurfaceMountL15/22/0.996714835067148460RL-1284-22-43RL1500-22PE-53815PE-53815-SDO3308-223L21/68/0.996714407067144450RL-5417-5RL1500-68PE-53821PE-53821-SDO3316-683L22/47/1.176714408067144460RL-5417-6-PE-53822PE-53822-SDO3316-473L23/33/1.406714409067144470RL-5417-6-PE-53823PE-53823-SDO3316-333L24/22/1.706714837067148480RL-1283-22-43-PE-53824PE-53825-SDO3316-223L25/15/2.106714838067148490RL-1283-15-43-PE-53825PE-53824-SDO3316-153L26/330/0.806714410067144480RL-5471-1-PE-53826PE-53826-SDO5022P334L27/220/1.006714411067144490RL-5471-2-PE-53827PE-53827-SDO5022P224L28/150/1.206714412067144500RL-5471-3-PE-53828PE-53828-SDO5022P154L29/100/1.476714413067144510RL-5471-4-PE-53829PE-53829-SDO5022P104L30/68/1.786714414067144520RL-5471-5-PE-53830PE-53830-SDO5022P683L31/47/2.206714415067144530RL-5471-6-PE-53831PE-53831-SDO5022P473L32/33/2.506714416067144540RL-5471-7-PE-53932PE-53832-SDO5022P333L33/22/3.106714439067144500RL-1283-22-43-PE-53933PE-53833-SDO5022P223L34/15/3.406714440067144790RL-1283-15-43-PE-53934PE-53834-SDO5022P153L35/220/1.7067144170-RL-5473-1-PE-53935PE-53835-S-L36/150/2.1067144180-RL-5473-4-PE-54036PE-53836-S-L37/100/2.5067144190-RL-5472-1-PE-54037PE-53837-S-L38/68/3.1067144200-RL-5472-2-PE-54038PE-53838-S-L39/47/3.5067144210-RL-5472-3-PE-54039PE-53839-S-L40/33/3.506714422067148290RL-5472-4-PE-54040PE-53840-S-L41/22/3.506714423067148300RL-5472-5-PE-54041PE-53841-S-L42/150/2.7067144410-RL-5473-4-PE-54042PE-53842-S-L43/100/3.4067144240-RL-5473-2-PE-54043-L44/68/3.4067144250-RL-5473-3-PE-54044-Table1.ProductmodelofaninductormanufacturerInmostcases,wecanuselowequivalentresistanceelectrolyticcapacitorsorsolidtantalumcapacitorsbetween82uF~820uF.Wheninuse,thecapacitorshouldbeclosetotheforLM2596-ADJIC,andthepinsandconnectingcopperwiresshouldbeasshortaspossible.SeeTable2below.Inordertosimplifytheselectionofcapacitors,Table1containsthedifferentoutputvoltagesandoutputcapacitorsrequiredforthebestdesign.Thewithstandvoltageofthecapacitorisatleast5timestheoutputvoltage.Sometimes,inordertoobtainalowerrippleoutputvoltage,ahighercapacitorwithstandvoltagevalueisrequired.Thisblogchooses220uF/50Velectrolyticcapacitors.VOUTIn-LineCapacitorSurfaceMountCapacitorPANASONICHFQ(F/V)NICHICONPL(F/V)FeedforwardCapacitorAVXTPS(F/V)VISHAY595D(F/V)FeedforwardCapacitor2820/35820/3533nF330/6.3470/433nF4560/35470/3510nF330/6.3390/6.310nF6470/25470/253.3nF220/10330/1033nF9330/25330/251.5nF100/16180/161.5nF12330/25330/251nF100/16180/161nF15220/35220/35680pF68/20120/20680pF24220/35150/35560pF33/2533/25220pF28100/50100/50390pF10/3515/50220pFTable2.OutputCapacitorandFeedforwardCapacitorSelection4)FeedforwardCapacitorCFFWhentheoutputvoltageislarge,acompensationcapacitorwithatypicalvaluebetween100pFand33nFisrequired,whichisconnectedinparallelwiththeoutputvoltageadjustmentresistorR2.Itsfunctionistocompensatethefeedbackloopandincreasethephasemargintoimprovethestabilityoftheloop.Forhighoutputvoltage,lowinput-outputvoltageand/orlowequivalentresistanceoutputcapacitors,thiscapacitormakesthecircuitmorestable,suchassolidtantalumcapacitors.TheselectionstillreferstothecorrespondingfeedforwardcapacitorvalueinTable1.Thisblogchooses33nFceramiccapacitors.CFF=1/(31*1000*R2)Thiscapacitorcanbeaceramiccapacitor,plasticormicacapacitor.5)ZenerDiode(D1)SelectionThemaximumcurrentcapacityoftheZenerdiodeisatleast1.3timesthemaximumloadcurrent.Ifthedesignedpowersupplyistowithstandcontinuousshort-circuitoutput,themaximumcurrentcapacityoftheZenerdiodeisequaltothelimitoutputofLM2596Current.Itsfunctionistoprovideapathfortheinductorcurrentwhentheswitchisclosed.ThereversevoltageoftheZenerdiodeisatleast1.25timesthemaximumoutputvoltage;theZenerdiodemustbeafastrecoverydiodeandmustbeclosetotheLM2596-ADJIC.Atthesametime,thepinsandtheconnectedcopperwiresshouldbeshort.Therefore,weshouldfirstchooseSchottkydiodes.Thisblogchooses1N5825Schottkydiodehere.6)InputCapacitanceCINTheinputcapacitorisanelectrolyticcapacitorortantalumcapacitorwithalowequivalentresistance,whichisalsoclosetotheIC,andtheDCloadcurrentmustexceedtwicetherootmeansquareoftheinputcapacitorcurrent.Foraluminumelectrolyticcapacitors,themaximuminputvoltageis2/3ofthewithstandvoltage;fortantalumcapacitors,selectcapacitorsthatthemanufacturerhastestedforsurgecurrent.Wecanselecttheappropriateinputcapacitanceaccordingtothegraphshown.Thiscapacitorpreventsexcessivetransientvoltagefromappearingattheinput,andatthesametimeprovidestransientcurrentforLM2596-ADJeverytimeitswitches.Thisbloguses680uF/50Velectrolyticcapacitors.VROutputCurrent:3AOutputCurrent:4A~6ALnlineSurfaceMountLnlineSurfaceMountSchottkySuperFastRecoverySchottkySuperFastRecoverySchottkySuperFastRecoverySchottkySuperFastRecovery20VTheminimumwithstandvoltageofallsuchdiodesis50VMURS32030WF10IN5820Theminimumwithstandvoltageofallsuchdiodesis50VMURS320Theminimumwithstandvoltageofallsuchdiodesis50VMURS62050WF10SR502Theminimumwithstandvoltageofallsuchdiodesis50VMURS620HER601SK32SR302IN5823MBR320SB52030V30WQ03IN5821SK33MBR33050WQ03SR50331DQ03IN582440VIN5822SB530SK34SR30450WQ04SR504MBRS340MBR340IN582530WQ0431DQ04SB54050VorHigherSK35SR305MBRS360MBR35050WQ05SB55030WQ0531DQ0550SQ080Table3.ChoiceofDiodeFigure4.LM2596-ADJapplicationinformationIIIHowtoApplyandUseLM2596SteplessAdjustableDCPowerSupply3.1HowtoApply?ThedevicecanbeusedasapowersupplythatrequiresaDCvoltagesourcekit:radiopowersupplydoorbellpowersupplyalarmpowersupplypoweramplifierpowersupply51single-chippowersupply,etc.3.2HowtoUse?Theanodeoftheoutputend(redalligatorclip)isconnectedtotheanodeofthecircuit,andthecathodeoftheoutputend(blackalligatorclip)isconnectedtothecathodeofthecircuit.Plugthe220Vpowercordintothemainssocket.Turnonthepowerswitch,theDCvoltagesourceindicator(red)willlightup,adjusttheknobtooutputthevoltagechange,anditsvaluewillbedisplayedonthevoltmeterhead.FAQWhatislm2596?TheLM2596seriesofregulatorsaremonolithicintegratedcircuitsthatprovidealltheactivefunctionsforastep-down(buck)switchingregulator,capableofdrivinga3-Aloadwithexcellentlineandloadregulation.WhatisthedifferencebetweenLM2596andLM2595?LM2596:Thehighestoutputcurrentis3A,1PIN-VOUT,2PIN-VIN;LM2595:Thehighestoutputcurrentis1A,1PIN-VIN,2PIN-VOUT.WhatisthevoltageofeachpinofLM2596-12?Whatisthefunctionofeachpin?Pin1istheinputterminal,12V,thenormalworkingvoltagerangeshouldbe14V~37Vundertheoutputcondition;pin2istheoutputterminal,hereisthehigh-frequencyoscillationoutput,notDCvoltage,sothereisnodefinitevoltage;pin3isgrounded,0V;Pin5istheenablecontrolterminal,LM2596worksnormallywhenconnectedtoalowlevel,andnooutputisturnedoffwhenconnectedtoahighlevel,usuallydirectlygrounded;Pin4isthefeedbackcontrolsignalinputterminal,connectedtothemiddleconnectionpointoftheproportionalresistor,wherethevoltageItisproportionaltotheactualoutput.CanLM2596outputnegativevoltage?LM2596canoutputnegativevoltage.LM2596hasdifferentapplicationcircuits,whichcanoutputpositivevoltageornegativevoltage,butithasnoboostfunction,andtheabsolutevalueofitsoutputvoltagemustbelessthantheabsolutevalueoftheinputvoltage.Inthecircuitwithadjustableoutputvoltageoflm2596,cantheoutputvoltagebegreaterthantheinputvoltage?TheLM2596switchingvoltageregulatorisastep-downpowermanagementmonolithicintegratedcircuit,whichcanoutput3Adrivecurrentandhasgoodlinearityandloadregulationcharacteristics.Theoutputvoltagewillnotbegreaterthantheinputvoltage.Iftheoutputvoltageisgreaterthantheinputvoltage,itisbesttouseastep-uppowerchip.SuchasXL6009,VT1050.Afterreadingtheblog,haveyoubetterunderstandLM2596?Finally,ifyouhaveanyquestionsaboutLM2596,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!