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时间:2021-04-23 00:46:29 来源:网络整理编辑:DEFINEDDR4

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Moreover it is also an ideal transistor to use for hobby and educational electronics projects.

Moreover it is also an ideal transistor to use for hobby and educational electronics projects.

com/datasheet-pdf/view/609126/FAIRCHILD/SS9015/+408248VDvHSEIlOpf/1aHvCh+/datasheetApplications:Audio PreamplifiersAudio Amplifier StagesSignal AmplificationSensor CircuitsSwitching loads under 100mADarlington PairsHow to Safely Long Run in a Circuit:Getting long term performance with this SS9014 it is suggested to not drive load of more than 100mA and 45V through this transistor.

DEFINEDDR4

the maximum DC current gain of the transistor is 1000.push({});Where We Can Use it How to Use:The SS9014 is designed to use for low noise and hi gain audio preamplifier circuits but it can also be used to amplify any type of low gain signals.The max collector dissipation of 400mW also makes it capable to drive a small 2 to 3 inch 4 Ohms or 8Ohms speaker.

DEFINEDDR4

But it is also capable to use as a switch for driving load of 45V and 100mA.Moreover it can also be used as audio amplifier or in audio amplifier stages.

DEFINEDDR4

Moreover it can also perform well in RF circuits under 150MHz.

(These are the nearest possible equivalent or replacement transistors for SS9014.IDescriptionTL431isa3-terminaladjustableshuntreferencevoltagesourcewithgoodthermalstability.Also,TL431isalsocalledavoltageregulatoror3-terminalsamplingintegratedcircuit.ItsoutputvoltagecanbearbitrarilysettoanyvalueintherangefromVref(2.5V)to36Vwithtworesistors.ThetypicaldynamicimpedanceofTL431is0.2.Becauseofitsgoodperformanceandlowprice,itiswidelyusedinvariouspowercircuits.TL431AdjustableZener-HowtoUseitCatalogIDescriptionIITL431FeaturesIIITL431FunctionalBlockDiagramIVTL431WorkingPrincipleVTL431ApplicationNotes5.1ReduceOutputNoise5.2Current5.3PowerConsumption5.4SelectionofSamplingResistorsR1andR25.5MinimumMaintenanceCurrentandMinimumCathodeVoltageVIConclusionComponentDatasheetFAQOrderingQuantityIITL431FeaturesFeaturesofTL431regulatorareasfollows:ReferenceVoltageToleranceat25C0.5%(BGrade)1%(AGrade)2%(StandardGrade)AdjustableOutputVoltage:Vrefto36VOperationFrom40Cto125CTypicalTemperatureDrift(TL43xB)6mV(CTemp)14mV(ITemp,QTemp)LowOutputNoise0.2-TypicalOutputImpedanceSink-CurrentCapability:1mAto100mAIIITL431FunctionalBlockDiagramTheencapsulationformofTL431isthesameasthatofplastic-encapsulatedtransistor9013.AsshowninFigure1(a).Similarproductsalsohavethedualin-lineshapeshowninFigure1(b).Ithas3pins:CathodeAnodeReferenceTerminalTheyareabbreviatedasC,A,andRrespectively,andthesymbolsinthecircuitareshowninFigure1(c).Figure1.TL431PinoutandSimplifiedSchematicFigure2isaschematicdiagramoftheTL431FunctionalModules.Ascanbeseenfromthefigure,Vrefisaninternal2.5Vreferencesource,connectedtotheinvertinginputoftheoperationalamplifier.Itcanbeknownfromthecharacteristicsoftheop-ampthatonlywhenthevoltageattheREFterminal(non-invertingterminal)isveryclosetoVref(2.5V),astable,non-saturatedcurrentwillpassthroughthetransistor.AndwiththeslightchangeinthevoltageoftheREFterminal,thecurrentthroughthetransistorwillchangefrom1to150mA(thisfigureisbynomeanstheactualinternalstructureoftheTL431,itisonlyusedtoanalyzethefunction).Figure2.TL431FunctionalModuleIVTL431WorkingPrincipleTL431isequivalenttoanadjustableZenervoltageregulator,andtheoutputvoltageissetbyanexternalprecisiondividerresistor.InthecircuitshowninFigure2,whentheresistancevaluesofR1andR2aredetermined,thetwointroducefeedbacktothepartialpressureofV0.IfV0increases,thefeedbackamountincreases,andtheShuntofTL431increases,whichinturnleadstoV0decline.Obviously,thenegativefeedbackcircuitofthisdepthmustbestablewhenthevoltageattheREFterminalisequaltothereferencevoltage,atthistimeV0=(1+R1/R2)Vref.ChoosingdifferentvaluesofR1andR2cangetanyvoltageoutputrangingfrom2.5Vto36V.Inparticular,whenR1=R2,V0=5V.ItshouldbenotedthatthenecessaryconditionsfortheTL431toworkmustbeguaranteedwhenselectingtheresistor,thatis,thecurrentthroughthecathodemustbegreaterthan1mA.Figure3.Tl431EquivalentCircuitSothespecificWorkingPrincipleofTL431is:Whentheinputvoltageincreases,theoutputvoltageincreasesandtheoutputsamplingincreases.Atthistime,theinternalcircuitisadjustedtoincreasethecurrentflowingthroughitself.Thisalsoincreasesthecurrentlimitcircuit.Asaresult,thevoltagedropofthecurrentlimitingresistorincreases.Theoutputvoltageisequaltotheinputvoltageminusthecurrent-limitingresistanceandtheincreaseinvoltagedropcausetheoutputvoltagetodecrease.Soastoachievevoltageregulation.VTL431ApplicationNotes5.1ReduceOutputNoiseTheuseofTL431isverysimilartotheuseofZenerdiode.WhentheZenerdiodeworksinthecircuit,itwillproduceanirregularperiodicnoise.ThiskindofirregularnoiseiscalledZenernoise.AlthoughthelevelofZenernoiseisnothigh,itisoneoftheimportantreasonsthataffecttheoutputcharacteristicsoftheZenerdiode.WecanusecapacitorsinparalleltoabsorbtheZenernoiseofthesecondregulator.Inthisway,theoutputcharacteristicsoftheZenerdiodecanbeimproved.Inaddition,thecapacitorconnectedinparalleltotheZenerdiodecanalsoabsorbtherippleofthepowersupply,makingtheoutputvoltageoftheZenerdiodemorestable.Secondly,whentheZenerdiodeisusedinparallelwiththecapacitor,duetothechargingeffectofthecapacitor,thesettlingtimeoftheoutputvoltageoftheZenerdiodewillincreaseandtheoutputvoltagewillriseslowly.However,thisisonlythemomentwhenthepoweristurnedon.Figure4.TL431ShuntRegularDuringnormaloperation,theoutputvoltageoftheZenerdiodeiscompletelystable.ButwhentheTL431isconnectedinparallelwiththecapacitorandtheselectedcapacityvalueisnotsuitable,sometimesitnotonlydoesnotplayagoodrole.Thiswillcauseoscillationinstead.Because,thecurrentflowingthroughTL431hasacertainrelationshipwiththecapacityofthecapacitor.Experimentsshowthatifacapacitorwithacapacitanceof0.01~3FisconnectedinparallelontheTL431,itislikelytocausetheTL431tooscillate.Therefore,whenTL431isusedinparallelwithacapacitor,thevalueofthecapacitorinparallelwithTL431shouldbegreaterthan3Forlessthan0.01F,whichmustbepaidattentionto.Butwhentheoutputvoltageisgreaterthan15VandIKisgreaterthan10mA,theoccurrenceofoscillationcanbecompletelyavoided.Whenweareinactualapplication,itisrequiredtoconnecta33uF/10Vtantalumcapacitorinparallelora47uF/16Velectrolyticcapacitorinparallel.5.2CurrentForthecurrentflowingthroughTL431:Theminimumcurrentmustbegreaterthan1mA,otherwisethevoltageregulationperformancewillbelost.Themaximumcurrentcannotexceed100mA,otherwisetheTL431willbedamaged.Therefore,thechoiceofthecurrent-limitingresistorisveryimportant.5.3PowerConsumptionForexample,thecommonTO-92packageTL431hasamaximumpowerconsumptionof0.7W.TheactualconsumptionofTL431inthecircuitis:P=Vo*IVoistheoutputvoltage;IisthecurrentthroughTL431;Therefore,TL431canonlyoutput140mAcurrentwhentheoutputdoesnotexceed5V,andcanonlyoutput100mAcurrentwhentheoutputvoltageis7V.Thisisbecauseofthepowerconsumptionlimitation.Theconventionalpowerconsumptionis0.5~1.2W.Whenitisusedunderhightemperature,highpressure,orhighcurrentconditions,attentionshouldbepaidtoventilation,heatdissipation,andsafety.5.4SelectionofSamplingResistorsR1andR2Doyouknow?Theselectionandplacementofthesamplingresistorcandirectlyaffectthevoltageregulationaccuracyandtemperaturecharacteristics.Therefore,thesametypeofprecisionresistorswithsmalltemperaturecoefficient,lownoiseandhigh-powermarginmustbeselected.AccordingtotheformulaVo=2.5(1+R1/R2),themaximumVois36V,andthemaximumratioofR1/R2canbecalculatedas13.4,thatis,R1is13.4timesthemaximumvalueofR2.BecauseTL431hashigheropen-loopgainandfasterresponsespeed,whenthesamplingpoint(theconnectionpointofR1andR2)isfarawayfromthetwopoles,thecircuitispronetoovershootandself-excitation.Sopayattentionwhenusingit.5.5MinimumMaintenanceCurrentandMinimumCathodeVoltageBecausetheinternalreferenceVrefofTL431ismaintainedbythecathodecurrentandislowerthanthevoltagebetweenelectrodes.Soweneedtopayattentionto:AftertheoutputpoleofTL431iscutoff,theremuststillbeacathodesustainingcurrentgreaterthan0.2mA.Whentheoutputpoleissaturated,thevoltagebetweenthepolesisstillatleast2.2V.VIConclusionThisblogsummarizesthefeatures,workingprincipleandprecautionsofTL431.Allinall,TL431isacompactdesign,easytouse,reliableperformanceandcost-effectiveregulatorbenchmark.Therefore,ithasawiderangeofapplications.ComponentDatasheetTL431DatasheetFAQWhatistheUseofTL431?TheTL431isaprogrammableprecisionreferenceandiscommonlyusedinswitchingpowersupplies,whereitprovidesfeedbackindicatingiftheoutputvoltageistoohighortoolow.Byusingaspecialcircuitcalledabandgap,theTL431providesastablevoltagereferenceacrossawidetemperaturerange.WhatisTL431Transistor?TheTL431isaRegulatorDiodewhoseoutputvoltagecanbeprogrammedbychangingthevalueofresistorsconnectedtoit.ItactsalmostlikeaZenerdiodeexceptforthatthevoltageratingofthisICisprogrammable.Itiscommonlyusedtoprovidenegativeorpositivevoltagereferences.HowdoesaShuntRegulatorWork?Theshuntregulatororshuntvoltageregulatorisaformofvoltageregulatorwheretheregulatingelementshuntsthecurrenttoground.Theshuntregulatoroperatesbymaintainingaconstantvoltageacrossitsterminalsandittakesupthesurpluscurrenttomaintainthevoltageacrosstheload.

ThisarticlefirstintroducedthethreecommonlyusedstableoutputvoltagecircuitsofUC3842,analyzedtheirrespectiveadvantagesanddisadvantages,anddesignedanewvoltagefeedbackcircuitonthisbasis.Experimentsprovethatthisnewcircuithasagoodvoltagestabilizingeffect.CatalogI.CommonVoltageFeedbackCircuits1.1Directvoltagedivisionoftheoutputvoltageastheinputoftheerroramplifier1.2Auxiliarypowersupplyoutputvoltagedivisionastheinputoftheerroramplifier1.3ChangetheinputerrorvoltageoftheerroramplifierusinglinearoptocouplerII.ExperimentsandResults2.1Changethegainoferroramplifierbyusinglinearoptocoupler2.2ExperimentalresultsIII.ConclusionI.CommonVoltageFeedbackCircuitsGenerally,thePWMtypeswitchingpowersupplyusessamplingoftheoutputvoltageasthefeedbackvoltageofthePWMcontroller.AfterthefeedbackvoltageispassedthroughtheerroramplifierinsidethePWMcontroller,thedutycycleoftheswitchingsignalisadjustedtoachievethestabilityoftheoutputvoltage.Butdifferentvoltagefeedbackcircuitshavedifferentoutputvoltagestabilityaccuracy.TheinternalcircuitdiagramofUC3842isshownasinFigure1.UC3842InternalCircuit1.1DirectvoltagedivisionoftheoutputvoltageastheinputoftheerroramplifierAsshowninFigure2,theoutputvoltageVoisdividedbyR2andR4andthenusedasasamplingsignalandinputtotheUC3842pin2(thereverseinputoftheerroramplifier).Theforwardinputoftheerroramplifierisconnectedtothereferencevoltageof2.5VinsidetheUC3842.Whenthesamplingvoltageislessthan2.5V,thevoltagedifferencebetweentheforwardandreverseoutputsoftheerroramplifierisamplifiedbytheamplifiertoadjusttheoutputvoltage,makingthedutycycleoftheoutputsignaloftheUC3842larger,theoutputvoltagerises,andfinallytheoutputvoltageisstabilizedatthesetvoltagevalue.R3andC1areconnectedinparalleltoformacurrent-typefeedback.Theadvantageofthiscircuitisthatthesamplingcircuitissimple,butthedisadvantageisthattheinputvoltageandoutputvoltagemustsharethesamegroundandcannotbeelectricallyisolated.Thisiseasytocausedifficultyinpowersupplywiring,andthepowersupplyworksinahigh-frequencyswitchingstate,whichiseasytocauseelectromagneticinterference,whichwillinevitablybringdifficultiesincircuitdesign,sothismethodisrarelyused.Figure2Samplingdiagramfordirectvoltagedivisionofoutputvoltage1.2AuxiliarypowersupplyoutputvoltagedivisionastheinputoftheerroramplifierAsshowninFigure3,whentheoutputvoltagerises,theinducedvoltagegeneratedontheauxiliarywindingofthesingle-endedflybacktransformerTalsorises,andthevoltageisrectified,filteredandregulatedbyD2,D3,C15,C14,C13andR15toobtainaDCvoltagetopowertheUC3842.Atthesametime,thevoltageisdividedbyR2andR4asasamplingvoltageandsenttotheUC3842spin2.Aftercomparingwiththereferencevoltage,itisamplifiedbytheerroramplifier,sothatthedutycycleofpin6outputpulsebecomessmallerandtheoutputvoltagedropstoachievethepurposeofvoltageregulation.Similarly,whentheoutputvoltagedecreases,thedutycycleoftheoutputpulseofpin6becomeslargerandtheoutputvoltagerises,finallystabilizingtheoutputvoltageatthesetvalue.Figure3SamplingDiagramforauxiliarypowersupplydivisionofoutputvoltageTheadvantageofthiscircuitisthatthesamplingcircuitissimple,andthereisnoelectricalpathbetweenthesecondarywinding,theprimarywindingandtheauxiliarywinding,whichiseasytowire.Thedisadvantageisthatthesamplingvoltageisnotobtaineddirectlyfromthesecondarywinding,andthevoltagestabilizationeffectisnotthatpositive.Itwasfoundintheexperimentthatthevoltagestabilizationbasicallycannotbeachievedwhentheloadofthepowersupplyvariesgreatly.Thecircuitissuitableforthecaseofafixedload.1.3ChangetheinputerrorvoltageoftheerroramplifierusinglinearoptocouplerAsshowninthefigure4,thevoltagesamplingcircuitoftheswitchingpowersupplyhastwocircuits:oneisthevoltageoftheauxiliarywindingthroughD1,D2,C1,C2,C3,R9rectification,filteringandvoltageregulationtoobtain16VDCvoltagetotheUC3842powersupply,inaddition,thevoltagethroughR2andR4voltagedivisiontoobtainasamplingvoltage,thesamplingvoltagemainlyreflectsthechangeoftheDCbusvoltage.Theotheristhephotocoupler,three-terminaladjustableregulatorZandR4,R5,R6,R7,R8voltagesamplingcircuit,theroadvoltagereflectsthechangeintheoutputvoltage;whentheoutputvoltagerises,thereferencevoltageoftheinputZalsorisesaftertheresistorR7andR8dividesthevoltage,theregulatorvoltagevalueoftheregulatorrises,thecurrentflowingthroughthelight-emittingdiodeinthephotocouplerdecreases,thecurrentflowingthroughthephototransistorinthephotocoupleralsocorrespondinglyreduced,theerroramplifierinputfeedbackvoltageisreduced,resultingintheUC3842pin6outputdrivesignaldutycyclebecomessmaller,sotheoutputvoltagedrops,toachievethepurposeofvoltageregulation.Figure4AuxiliarypowersamplingandoptocouplersamplingsynthesisSincethecircuitusesanopto-coupler,itachievestheisolationofoutputandinput,theisolationofweakandstrongpower,reducingelectromagneticinterference,thusitsanti-interferenceabilityisimproved,anditistotheoutputvoltagesampling,withgoodvoltageregulationperformance.Thedisadvantageofthecircuitistheincreaseinexternalcomponents,whichincreasesthedifficultyofwiringandaddsthecostofthepowersupply.II.ExperimentsandResults2.1ChangethegainoferroramplifierbyusinglinearoptocouplerAsshowninFigure5,thevoltagesamplingandfeedbackcircuitconsistsofR2,R5,R6,R7,R8,C1,opto-coupler,andthree-terminaladjustableregulatorZ.Whentheoutputvoltagerises,theoutputvoltageisdividedbyR7andR8toobtainthesamplingvoltage(i.e.,Zsreferencevoltage)alsorises,Zsregulatorvaluealsorises,thecurrentflowingthroughthelight-emittingdiodeinthephotocouplerdecreases,resultinginareductioninthecurrentflowingthroughthephototransistor.ThisisequivalenttoC1parallelvariableresistorresistancevaluebecomeslarge(theequivalentresistancevaluebytheflowoflight-emittingdiodecurrentcontrol),thegainoftheerroramplifierbecomeslarge,resultingintheUC3842pin6outputofthedrivesignaldutycyclebecomessmall,theoutputvoltagedropstoachievethepurposeofvoltageregulation.Whentheoutputvoltagedecreases,thegainoftheerroramplifierbecomessmallerandthedutycycleoftheoutputswitchingsignalbecomeslarger,whicheventuallystabilizestheoutputvoltageatthesetvalue.Becausethevoltagefeedbackinputpin2ofUC3842isgrounded,sotheinputerroroftheerroramplifierisalwaysfixed,andwhatchangesisthegainoftheerroramplifier(thephototransistorinthelinearoptocouplercanberegardedasavariableresistor),anditsequivalentcircuitdiagramisshowninFigure6.Figure5VaryingthegainoftheerroramplifierusinganoptocouplerFigure6EquivalentcircuitforchangingthegainoftheerroramplifierThecircuitchangestheoutputoftheerroramplifierbyadjustingthegainoftheerroramplifierinsteadofadjustingtheinputerroroftheerroramplifier,thuschangingthedutycycleoftheswitchingsignal.Thistopologynotonlyhasfewerexternalcomponents,butalsoemploysathree-terminaladjustableregulatorinthevoltagesamplingcircuit,makingtheoutputvoltageessentiallyunchangedwhentheloadchangessignificantly.Theexperimentprovesthatthecircuithasaverygoodvoltageregulationeffectcomparedwiththeabovethreefeedbackcircuits.2.2ExperimentalresultsThisnewvoltagefeedbackcircuitusingalinearoptocouplertochangethegainoftheerroramplifierisusedina48V/12Vsingle-endedflybackDC/DCswitchingpowersupply(maximumoutputcurrentof5A),whichshowsthattheoutputvoltageofthepowersupplyisstableandhasastrongloadcarryingcapability.Figure7(a)-(h)givestheoutputvoltageanddrivewaveformswhentheloadis100,25,10,and3,respectively.Fromthewaveforms,itcanbeseenthatwhentheloadcurrentgraduallyincreases,thedutycycleofthedrivesignalincreasesaccordingly,buttheoutputvoltageisalwaysstableat12.16V.Figure7OutputvoltageanddrivewaveformatdifferentloadsIII.ConclusionInthesingle-endedisolatedPWMpowersupply,thecurrent-modepulsewidthmodulatorUC3842hasawiderangeofapplications.ThisarticlesummarizesthevoltagefeedbackcircuitdesignthatusesalinearoptocouplertochangethegainoftheUC3842erroramplifier.Anditisprovedbyexperimentsthatthenewvoltagefeedbackcircuithashighvoltageregulationaccuracyandstrongloadadaptability.Inthisblog,Apogeewebhasprepared8simple2N3904circuitsforelectronicsenthusiasts.Thesecircuitdiagramsarebasicallybeginner-friendlytypes.Hopethesecircuitdiagramsarehelpfultoyou.Catalog2N3904CircuitsComponentDatasheetFAQ2N3904CircuitCircuit1:ThermostatcontrollercomposedofLM75intelligenttemperaturesensorand2N3904transisitorCircuit2Circuit3Circuit4Circuit5Circuit6:2N3904SampleCircuit-AmplifierCircuit7:Howtodesigna13.56mhzsinewavepoweramplifiercircuitwith2N3904Circuit8:Thenon-invertingcircuitusesapairofcomplementaryNPNtype(2N3904)andPNPtype(2N3906)transistorsComponentDatasheet2N3904DatasheetFAQWhatisa2N3904Transistor?The2N3904isacommonNPNbipolarjunctiontransistorusedforgeneral-purposelow-poweramplifyingorswitchingapplications.Itisdesignedforlowcurrentandpower,mediumvoltage,andcanoperateatmoderatelyhighspeeds.HowDoesa2N3904TransistorWork?2N3904isaNPNtransistorhencethecollectorandemitterwillbeleftopen(Reversebiased)whenthebasepinisheldatgroundandwillbeclosed(Forwardbiased)whenasignalisprovidedtobasepin.2N3904hasagainvalueof300;thisvaluedeterminestheamplificationcapacityofthetransistor.WhatisPNPNPN?PNPsensorsproduceapositiveoutputtoyourindustrialcontrolsinput,whileNPNsensorsproduceanegativesignalduringanonstate....NPN,orsinkingoutputsensors,workintheoppositeway,sinkinggroundvoltagetoaninputwhenitson.WhatsisATransistor?Atransistorisasemiconductordeviceusedtoamplifyorswitchelectronicsignalsandelectricalpower.Itiscomposedofsemiconductormaterialusuallywithatleastthreeterminalsforconnectiontoanexternalcircuit.WhatistheGainofaTransistor?Thecurrentgainforthecommon-baseconfigurationisdefinedasthechangeincollectorcurrentdividedbythechangeinemittercurrentwhenthebase-to-collectorvoltageisconstant.Typicalcommon-basecurrentgaininawell-designedbipolartransistorisveryclosetounity.

Aswehaveintroducedinthelastblog,UC3842isafixedfrequencycurrent-modePWMcontroller.ThisICisspeciallydesignedforOff-LineandDCtoDCconverterapplicationswithminimumexternalcomponents.Intheblogtoday,wellhaveafurtherdiscussionabouttheapplicationofUC3842intheboostconversioncircuit.CatalogBoostConversionCircuitOverviewI.CircuitModelofBoostConverterinDCMMode1.1MathematicalModelofDCMWorkingMode1.2WorkingConditionsofDCMModeII.DCMCircuitDesignBasedonUC38422.1DCMCircuitDesignBasedonAdder2.2UC3842WorkingPrincipleIII.SimulationandAnalysisofDCMModeCircuitIV.ConclusionBoostConversionCircuitOverviewBoostconverterscanreducetheoutputcurrentandthecapacitanceandvolumeoftheoutputfiltercapacitorunderacertainoutputpower,andarewidelyusedinswitchingpowersuppliesandelectronicballasts.Commonlyusedcontrolmethodsarevoltagefeedbackcontrolandcurrentfeedbackcontrol.Currentfeedbackcontrolcanforcetheinductorcurrenttotrackthereferencecurrentsignal,whichhastheadvantageoffastresponse.Whenworkingincontinuouscurrentmode(CCM),theBoostconverterneedstointroducemultiplefeedbackmethods.Whenworkingindiscontinuouscurrentmode(DCM),theconverterautomaticallyshapestheinputcurrent,andhasanaturalzero-currentturn-oncharacteristic,requiresasmallinductancevalue,simplecontrol,andissuitableforlow-powerapplications.Atpresent,therearemanyresearchesontheCCMmodeofBoostconversioncircuit,andmanycircuitmodelshavebeenestablished,andgratifyingresearchresultshavebeenobtained;theresearchonDCMmodeismainlyDC/DCcircuit,andtheresearchonDCMmodeinAC/DCcircuitVerylittle.Basedontherequirementsoflow-powerswitchingpowersupplywithlowcostandhighcostperformance,thispaperusestheuniversalUC3842chiptodesignaBoostconversioncircuit,analyzestheworkingcharacteristicsanddesignpointsoftheDCMmode,andsimulatestherationalityofthedesignedcircuitverification.I.CircuitModelofBoostConverterinDCMMode1.1MathematicalModelofDCMWorkingModeTheBoostconversioncircuitstructureisshowninFigure1(a).IntheCCMmode,theswitchingtubeMandthediodeVD5areturnedoninacomplementarymanner;whentheinductanceissmallortheswitchingcycleisrelativelylong,beforethestartofthenextcycle,thediodeVD5andMareallturnedoff,andtheBoostconversioncircuitworksinDCMmodeatthistime.Thecorrespondingwaveformbetweentheinductorcurrentandthepulsewidthmodulator(PWM)outputpulseisshowninFigure1(b).Figure1BoostconversioncircuitandDCMmodewaveformdiagramIntheK-thswitchingmodulationcycle,theon-offstatesoftheswitchtubeMandthediodeVD5satisfytherelationship:Tisthehigh-frequencymodulationperiodofPWM;KTistheK-thhigh-frequencymodulationperiodofPWM;D1Tistherisetimeoftheinductorcurrentinthehigh-frequencymodulationperiod;D2Tisthefalltimeoftheinductorcurrentinthehigh-frequencymodulationperiod;D3Tisthetimewhentheinductorcurrentiszerointhehighfrequencymodulationperiod.WhentheBoostcircuitworksinDCMmode,astheswitchtubeMandthediodeVD5turnonandoff,thestateofthesystemcanuseadifferentialequation:Intheformula,KT+D1T+D2T+D3T=(K+1)T;iL(t)istheinstantaneousvalueoftheinductorcurrent;in(t)istheinstantaneousvalueoftheinputvoltageonthegridside;o(t)isBoostTheinstantaneousvalueoftheconverteroutputvoltage.1.2WorkingConditionsofDCMModeItcanbeseenfromFigure1thattheinductorcurrentoftheBoostconverterinDCMmodeincreaseslinearlyfromzero.Ineachmodulationcycle,thereis:Whenthecircuitoutputfiltercapacitorislarge,theoutputvoltageripplecanbeignoredcomparedwiththeoutputvoltageamplitude,andtheoutputvoltageo(t)canberegardedasaconstanto.Inadual-loopcontrolsystem,thecurrent-loopreferencecurrentIrefisdeterminedbytheoutputofthevoltageouterloop,andthereis:Intheformula,r(t)istheinstantaneousvalueofthereferencevoltageprovidedbythevoltageloopforthecurrentloop;Rsisthesamplingresistancefordetectingthecurrent.Whentheinductorcurrentfollowsthesinusoidalinputvoltagewaveform,thepowerfactoriscloseto1,andtheavailabledutycycleD1canbeexpressedas:Intheformula,Vrefisthepeakvalueofr(t)inthepowerfrequencyperiod;Vinisthepeakvalueofin(t)inthepowerfrequencyperiod.Thesameprinciplecanbeobtained,ineachmodulationperiod,theexpressionofthedutycycleD2is:WhentheBoostconverterworksinthecriticalmode,thedutycyclesatisfiestherelationshipD1+D2=1.Fromthis,itcanbededucedthatthecriticalconditionfortheBoostcircuittoentertheCCMmodefromDCMis:WhenLLCRM,BoostcircuitworksinDCMmode;WhenLLCRM,BoostcircuitworksinCCMmode.Atthispoint,thefollowingconclusionscanbedrawn:(1)IntheDCMmode,theon-timeD1ToftheswitchtubeMisafixedvalue,whichdoesnotchangewiththesizeoftheinductorcurrent.(2)Whentheswitchisturnedoff,thetimeD2Twhentheinductorcurrentdropsto0changeswiththeoutputvoltageandinputvoltage.Thegreatertheinputvoltage,thegreatertheD2T,thegreatertheoutputvoltage,andthesmallertheD2T.II.DCMCircuitDesignBasedonUC38422.1DCMCircuitDesignBasedonAdderTheDCM-typeBoostcircuitincludestwocontrolloops,namelyavoltageloopandacurrentloop.Itsfunctionistoeliminatethegridcurrentspikes,sothattheinputcurrentbecomesasinusoidalshapeandisinphasewiththeinputvoltage.Forasingleswitchingcycle,thecurrentineachswitchingcycleisrequiredtobeproportionaltotheinputvoltage.Ifforsomereasontheoutputvoltageincreasesortheoutputcurrentincreases,thepulsewidthmodulatorwillchangethepulsewidthofthedrivesignal,thatis,thedutycycleD,sothattheaveragevoltageorpeakcurrentafterthechoppingwilldecrease.Soastoachievethepurposeofpowerfactorcorrection.TheDCMcircuitschematicdiagrambasedontheadderisshowninFigure2.Figure2DCMcircuitschematicdiagrambasedonadderThevoltageouterloopusesanaddertoreplacethemultipliercircuit.Thefeedbackvoltageonthegridsideisusedtoensurethatthecurrentsignalisasinusoidalsignal,andtheoutputfeedbackvoltageisusedtoensurethattheoutputvoltageisaconstantvalue.ThetwoaresynthesizedbytheadderU2.TheoutputsignalissenttotheerroramplifierintheUC3842currentloop,comparedwithagivenreferencevoltage,andthecomparisonresultissenttothecurrentmeasurementcomparator.ThepeakcurrentsignalL(t)oftheinductorinthemaincircuitissenttothecurrentmeasuringcomparatoratthesametime,thecomparisonresultofthetwoissenttotheRinputoftheRSlatchinthePWM,theclocksignaloutputbytheinternaloscillatingcircuitissenttotheSinputendoftheRSlatchinthePWM,whichworkstogethertocontroltheopeningandclosingoftheswitchtubeM1.2.2UC3842WorkingPrincipleUC3842isahigh-performancesingle-endedoutputcurrent-typePWMcontroller.ThecurrentcontrolloopiscomposedofaPWMlatch,acurrentdetectioncomparator,anerroramplifierandasawtoothoscillationcircuit.ItsinternalstructureisshowninFigure3.Figure3UC3842workingprinciplediagramUC3842cangenerateadrivesignalwithafixedfrequencyandadjustablepulsewidth.ExternalcomponentsRTandCTcanbeusedtosettheoscillationfrequencyandpreciselycontrolthedutycycle.TheoutputvoltageofUC3842canbeadjustedbycontrollingtheon-offstateoftheswitchtubetoachievethepurposeofvoltagestabilization.TheUC3842hasagoodvoltageregulationrate,goodfrequencyresponsecharacteristics,largestabilityamplitude,over-currentlimit,overvoltageprotectionandundervoltagelockoutfunction.Andithasfewerexternalpins,smallsize,isaneconomicalPWMdrivercontrolchip.III.SimulationandAnalysisofDCMModeCircuitInordertoverifythecorrectnessofthededucedcriticalconditionsandthedesignedcircuit,thedesignedcircuitwassimulatedandverifiedbyOrCAD10.5software.Whenthepowerinputispowerfrequencyalternatingcurrentanditscircuitparametersarein=311.13sin(t),o=385V,RL=1482Q,L=400H,theBoostconverterworksinDCMmode,anditsoutputvoltageandinductorcurrentwaveformsareasfollowsShowninFigure4.Figure4BoostconverteroutputvoltageandinductorcurrentwaveformThewaveformofthedutycycleatdifferenttimesisshowninFigure5.Figure5ThesizeofthedutycycleD1TatdifferenttimesIftheinductancevalueincreasesandexceedsthecriticalvalueLCRM,theinductorcurrentwillchangefromDCMmodetoCCMmode.WhentheinductancevalueL=1.2mH,Vo=508V,thewaveformisshowninFigure6.Figure6InductorcurrentwaveformwhenL=1.2mHThewaveformofthedutycycleD1TintheDCMstageisshowninFigure7Figure7ThedutycycleoftheDCWIphasewhentheinductanceexceedsthecriticalvalueItcanbeseenfromthesimulationresultsthatintheDCMmode,theon-timeoftheswitchisafixedvalue.WhentheinductanceLisgreaterthanthecriticalvalue,therewillbeatransitionfromDCMtoCCM.TheCCMmodeappearsnearthepeakofthepowerfrequencycurrent.IV.ConclusionThistextsummarizestheBoostconversioncircuitdesignschemebasedonUC3842chip.ByanalyzingthecircuitofBoostconverterinDCMmode,thecircuitmodelofBoostconverterinDCMmodeisestablished,andthedutycyclechangeruleinthismodeandthecriticalconditionsforenteringCCMmodefromDCMmodearestudied.UsingtheuniversalPWMmodulatorUC3842chip,aBoostconversioncircuitbasedontheprincipleofadditionisdesigned,andthecorrectnessoftheconclusionsobtainedisverifiedbysimulationsoftware.ThecircuitsimulationresultsshowthatthedesignedDCMcircuitcanmeettherequirementoftheinductorcurrenttofollowthevoltagewaveformcompletelyandachievethepurposeofimprovingthepowerfactor.Thisresearchprovidesdesignideasforthedevelopmentoflow-costlow-powerswitchingpowersupplies.UC3842isafixedfrequencycurrent-modePWMcontroller.ThisICisspeciallydesignedforOff-LineandDCtoDCconverterapplicationswithminimumexternalcomponents.ThisblogwillprovideyouthedetailedinformationofUC3845thePWMcontrolleraboutitspinout,features,applications,equivalents,whereandhowtousethisdevice,etc.CatalogUC3842PinoutUC3842FeaturesUC3842ParametersUC3842AbsoluteMaximumRatingsUC3842FunctionalBlockDiagramUC3842EquivalentsWheretouseUC3842ICHowtouseUC3842ICUC3842ApplicationsUC3842PackageComponentDatasheetUC3842PinoutNote:UC3842ICalsocomesin14-Pin,16-Pin,and20-Pinpackages.Thisarticlecoversonlythe8-PinversionoftheIC.PinNumberPinNameDescription1COMP(Comparator)Itisanoutputpinthatoutputslowimpedance1MHzsignal,basedonthedifferencebetweenthesetandcurrent-voltage.ItisnormallyconnectedtothevoltagefeedbackpinoftheICthrougharesistorandcapacitor.2VFB(VoltageFeedback)ItisaninputtotheerroramplifierinsidetheIC.Thedifferenceinvoltagelevelissuppliedtothispin3CurrentSenseAshuntresistorisusedtomonitorthecurrentthroughthecircuit,andthevoltageacrossitisprovidedasafeedbacktothecurrentsensepin4RT/CT(TimingResistor/TimingCapacitor)TheIChasaninternaloscillatorwhichcanbesetusinganexternalresistorandcapacitorconnectedtothispin.5GroundConnectedtothegroundofthecircuit6OutputThispinoutputsthePWMsignalbasedonthefeedbackprovidedandwecanusethistoswitchthepowerelectronicdevice.7VccSupplyvoltagefortheIC(Nominal11V)8VREFReferencevoltagebasedonwhichthePWMsignalisproduced.UC3842FeaturesOptimizedforoff-lineandDC-to-DCconvertersLowstart-upcurrent(1mA)AutomaticfeedforwardcompensationPulse-by-pulsecurrentlimitingEnhancedload-responsecharacteristicsUndervoltagelockoutwithhysteresisDouble-pulsesuppressionHigh-currenttotem-poleoutputInternallytrimmedbandgapreferenceUpto500-kHzoperationErroramplifierwithlowoutputresistanceUC3842ParametersTopologyBoost,Buck,Buck-Boost,Flyback,ForwardControlmethodPeakCurrentModeVCC(Min)(V)16VCC(Max)(V)28Dutycycle(Max)(%)100UVLOthresholdson/off(V)16/10Frequency(Max)(kHz)500Operatingtemperaturerange(C)0to70Gatedrive(Typ)(A)1FeaturesAdjustableSwitchingFrequency,CurrentLimiting,DeadTimeControl,ErrorAmplifier,Multi-topologyRatingCatalogUC3842AbsoluteMaximumRatingsUC3842FunctionalBlockDiagramUC3842FunctionalBlockDiagram(Toggle)UC3842EquivalentsPartNumberDescriptionManufacturerUC3842ANG4POWERCIRCUITS30-V,1A,500KHzcurrentmodePWMcontrollerwith16V/10VUVLO100%dutycycle,0Cto70C8-PDIP0to70TexasInstrumentsUC3842NPOWERCIRCUITS1ASWITCHINGCONTROLLER,500kHzSWITCHINGFREQ-MAX,PDIP8,0.300INCH,MINI,DIP-8STMicroelectronicsCS-3842BN8POWERCIRCUITSSwitchingController,Current-mode,1A,500kHzSwitchingFreq-Max,BIPolar,PDIP8,CherrySemiconductorCorporationIP3842AJPOWERCIRCUITS1ASWITCHINGCONTROLLER,500kHzSWITCHINGFREQ-MAX,CDIP8,CERAMIC,DIP-8TTElectronicsPowerandHybrid/SemelabLimitedUC3842ANPOWERCIRCUITS1ASWITCHINGCONTROLLER,500kHzSWITCHINGFREQ-MAX,PDIP8,PLASTIC,DIP-8MotorolaMobilityLLCUC3842AN2POWERCIRCUITS1ASWITCHINGCONTROLLER,500kHzSWITCHINGFREQ-MAX,PDIP8,PLASTIC,DIP-8ONSemiconductorUC3842BNGPOWERCIRCUITSHighPerformanceCurrentModePWMController,8LEADPDIP,50-TUBEONSemiconductorCS3842BGN8POWERCIRCUITS1ASWITCHINGCONTROLLER,PDIP8,0.300INCH,PLASTIC,MS-001,DIP-8ONSemiconductorUC3842NG4POWERCIRCUITSSingleended500KHzcurrentmodePWMcontrollerwith16V/10VUVLO100%dutycycle,0Cto70C8-PDIP0to70TexasInstrumentsWheretouseUC3842ICTheUC3842ICisacurrentmodePWMcontroller,whichmeansthatitcanbeusedtoprovideconstantcurrentbyvaryingtheoutputvoltagetotheload.ThisICfeaturesatrimmedoscillatorforprecisedutycyclecontrol,atemperature-compensatedreference,ahighgainerroramplifier,acurrentsensingcomparator,andahighcurrenttotempoleoutputforpowerMOSFEToperation.UC3842canbeusedtoregulateorlimitcurrentinapplicationssuchasSMPS,RPS,DC-DCConverters,Linevoltageregulators,etc.SoifyourelookingforanICtoproducePWMsignalstocontrolapowerswitchbasedonthecurrentflowingthroughthecircuit,thisICmightbetherightchoiceforyou.HowtouseUC3842ICItsprettysimpletouseUC3842inacircuit.DownbelowisasamplecircuitdiagramfromUC3845datasheet.UC3842ApplicationCircuitTheinputvoltagefortheVCCpinshouldbe12Vto28V.TheoutputpinoftheICisconnectedtothegateconductorcircuitofthepowerswitchtobeswitched.TheVFB(VoltageFeedback)pinactsasfeedbackonthebasisofwhichthePWMsignaliscontrolled.Theshuntresistorisusedtomonitorthecurrentchangeinthecircuit,andthenthisvoltagedifferenceovertheshuntisprovidedtothefeedbackpin.VREFisusedtoprovidechargingcurrentthroughthetimingresistortotheoscillatortimingcapacitor.ItisimportantforreferencestabilitythatVREFisroutedtoGROUNDwithaceramiccapacitorconnectedasclosetothepinaspossible.UC3842ApplicationsSMPS(SwitchModePowerSupplies)circuitsDC-DCconvertercircuitsElectronicspowersupplyBatterydraincircuitLoadmachinesUC3842PackageComponentDatasheetUC3842Datasheet