The33rdAnnualConferenceoftheIEEEIndustrialElectronicsSociety(IECON)Nov.5-8,2007,Taipei,TaiwanADemagnetizationCircuitforSingle-EndedForwardConverterT.J.LiangK.C.TsengJ.F.ChenR.L.LinPowerElectronicsLaboratoryDepartmentofElectricalEngineeringNationalCheng-KungUniversityNo.1,Ta-HseuhRoad,TainanCity,Taiwan,R.O.C.Email:ccskgctu.edu.tw,tjlianggmail.ncku.edu.twstoredisdissipatedintheresistoroftheRCDnetwork.Abstract-ThispaperpresentsanoveldemagnetizationHowever,thisdissipationnotonlyreducesefficiency,butschemeforsingle-endedforwardconverter.Inthepast,manyalsocreatesathermaldesignproblem.Inaddition,thepriortransformercoreresetmethodshavebeenproposedinforwardconverterwitharesonantresetisasimplemethodordertoavoidthetransformersaturation,suchastertiarytransformerwinding,RCDclamp,resonantreset,activeclampforcorereset.Withouttheuseofanyadditionalpartstoandtwo-switchforwardtopologyetc..However,theloweraccomplishtransformerdemagnetization,theresonantresetefficiency,complicatedtransformerwindingstructureandtheforwardconverter[7,8]isabletoreachtransformercoreresetcostoftoomanyaddedelementsarethemaindrawbacks.Inbyusingtheresonantofparasiticdevices.Thedisadvantagesthispaper,anoveldemagnetizationschemeforsingle-endedarethatthevoltagestressisstillhigherthansomeofthelaterforwardconverterispresented.Theproposeddemagnetizationtechniquesandhardtomaintaintheresetcondition.Incircuitisverysimpleandthetransformerdemagnetizationcanbereachedbyaddingtwodiodesandaclampingcapacitor.Inpracticalhighinputvoltageapplications,atwo-switchaddition,thetransformerdesignandPWMcontrolcircuitforforwardconverter[9,10]isoftenappliedinordertouselowerthesingle-endedforwardconverterwithproposedvoltageratingofpowerswitch.Duringthetwomainswitchesdemagnetizationcircuitisthesameasconventionalforwardareturnedoff,thetransformerisresetbyreturningtheconverter.Finally,theoperationandcircuitperformanceofthemagnetizingenergystoredtotheinputsourcethroughthesingle-endedforwardconverterwithproposeddemagnetizationtwoaddeddiodes.Duetotheschemeneedsanadditionalcircuitaredemonstratedwithanexperimentalprototypethatdeliversa5V/1OAoutputfroma36-72Vinputatthemaximumswitchandahighsidedriver,thecostofaddedelementsisincreased.Furthermore,anotherwaytoachievetransformerefficiencyof88%.demagnetizationistouseactiveclamptechnique[11,12],whichnotonlyclampsthevoltagestressacrossthemainswitch,butalsotoaccomplishzerovoltageswitching(ZVS)I.INTRODUCTIONBasedonthelowcost,circuitsimplicity,highefficiencyandreducedEMI/RFI.Thedisadvantagesaretheneedforanandhighreliability,forwardconverteriswidelyusedforlowadditionalswitchanditsassociatedhighsidegatedriver.Inthedemagnetizingcircuitsofforwardconverteraretomiddlepowerapplications.Ingeneral,itisnecessarytoresettransformercorefluxforsingle-endedforwardmentionedabove.Atertiarywindingresethastheconverterduringmainswitchofftimetopreventtransformercomplicatedtransformerwindingstructure.AnRCDresetcoresaturation.Therefore,anadditionalcircuitrymustbehasthelowestcost.Aresonantresethasthelowestelementsaddedtoovercomethetransformersaturationproblemsincount.Atwo-switchschemehasthelowestvoltagestress.Anforwardconverter.InordertoavoidtransformercoreactiveclampresethasthebestefficiencyandEMI/RFIsaturation,manypriorcorefluxresettechniques[1-3]haveperformances.Forabovedemagnetizingcircuits,sincethebeenproposedtosolvethisproblem.Theresetschemeofthetransformermagnetizingenergyisdissipatedorrecycledbyclassicforwardconverter[4,5],istoresetthecorefluxbytheadditionaldemagnetizingmechanisms,thetransformerisreturningthemagnetizingenergytotheinputsourceviaaabletoachievecorereset.However,thecomplicatedtertiarytransformerwindinginserieswithadiode.Sincethetransformerwinding,theextracostoftheaddedelementsandmagnetizingenergyisrecycledtotheinputsource,thethetransformermagnetizingenergyisdissipatedarethemainefficiencycanbeimprovedbythismechanism.However,thedrawbacks.Therefore,anoveldemagnetizationschemeforextrawindingmakesthetransformermoredifficulttodesignsingle-endedforwardconverterisproposedinthispaper.Theproposeddemagnetizationcircuitisacombinationoftwoandtoimplement.Othertransformercoreresetmethodsofforwardconverteraddeddiodesandaclampingcapacitor,whichcanrecycletheforhighswitchingfrequencyoperationarebrieflydescribedmagnetizingenergystoredinordertoresettransformercoreasfollows.Sincethecircuitsimplicity,AnRCDclampingflux.Duetothetransformerresetwithoutusingtheextraresetcircuit[6]isfavorableusedformanylowtomediumadditionalwinding,thetransformerwindingwindowareaispowerandcost-effectiveforwardconverters.Byusingtheabletoimprove.Also,thevoltagestressacrossmainswitchisRCDresetnetwork,thetransformermagnetizingenergydirectlyproportionaltoinputvoltagebythisproposedS.K.Changchien1-4244-0783-4/07/$20.00C2007IEEE1390demagnetizationcircuit.Moreover,thedesignofthetransformerforforwardconverterwiththisproposeddemagnetizationcircuitisthesameprocessastraditionalforwardconverter.Therefore,byusingthisproposeddemagnetizationcircuit,thedesignofforwardconverterisstilluncomplicated.Inthispaper,theproposeddemagnetizationcircuitsystemisanalyzedanddiscussed.Thesimulationandexperimentalresultsfora5V/1OAprototypesingle-endedforwardconverterataswitchingfrequencyoflOOkHzispresentedtoverifytheanalysisandperformanceoftheproposeddemagnetizationcircuit.II.PROPOSEDCONVERTERAforwardconverterwithtraditionalresetschemeisshowninFig.1.ThemagnetizingenergyistransferredtotheinputsourcebythetertiarytransformerwindingNrinserieswithadiodeDrwhilethemainswitchisturnedoff.Inordertoresettransformercorefluxandsavingthetransformerwindingwindowarea,thesingle-endedforwardconverterwiththisproposeddemagnetizationcircuitispresentedinFig.2.Intheprimaryside,theDCinputvoltagesourcevin,,transformerT,andmaintransistorswitchSare(1)Allsemiconductorelementsareideal.(2)TheoutputfilterinductanceLoislargeenoughthattheinductorcurrentiLoisconsideredasaconstantduringoneswitchingperiod.(3)TheoutputcapacitanceCOislargeenoughtoassumethattheoutputvoltagevoisaconstantvalueduringoneswitchingperiod.(4)Theleakageinductanceisnegligiblesinceitismuchsmallerthanmagnetizinginductance.Fig.1.Forwardconverterwithtertiarytransformerwindingcircuitthebasicelementsintheprimarysideoftheforwardconverterforpulsewidthmodulation(PWM)operation.TheprimarywindingoftransformerT1isacombinationofthewindingsN.,andNp2.ThedemagnetizationcircuitconsistsoftwodiodesD3,D4andoneclampingcapacitanceCc,whichareusedtorecyclethemagnetizingenergyforpreventingtransformercoresaturation.ThemagnetizingenergyisabsorbedviatheclampingcapacitanceCcandthediodeD3whilethemainswitchoffperiod.ThemagnetizingenergystoredintheclampcapacitanceCcisreleasedtooutputbythetransformerwindingNp2andthediodeD4duringtheswitchisturnedon.Inthesecondside,therectifierdiodesD1andD2,outputinductanceLoandoutputcapacitanceCoarethebasicdevices.TherectifierdiodeD1isusedtotransferenergyfrominputtooutputduringmainswitchonperiod.TherectifierdiodeD2carriestheinductorcurrentwhenthemainswitchisturnedoff.TheoutputfilterinductanceLoandcapacitanceCOareusedtoreducetheinductorcurrentandoutputvoltageripples.Withouttheuseofaddedextratransformerwinding,theproposeddemagnetizationcircuitisstillabletorecyclemagnetizingenergyinordertoavoidtransformersaturation.Thereforetransformerwindingstructureandwindingwindowareacanbeimproved.Also,thevoltagestressacrossmainswitchisdirectlyproportionaltoinputvoltage.Fig.3showsthekeywaveformsoftheforwardconverterwiththisproposeddemagnetizationscheme.Tosimplifytheanalysisofthesingle-endedforwardconverterwiththisproposeddemagnetizationschemebeginsbymakingtheseassumptions:IrwcictiISIJVDVGS5isTheessentialcircuitoperationalmodesforcontinuous-conductionmode(CCM)aredescribedinthefollowing.Baseontheaboveassumptions,fortheessentialcircuitoperationalanalysis,therearefourdifferentoperatingstatesintheproposedconverterduringoneswitchingperiodundercontinuousconductionmode(CCM).TheconductionmodesoftheswitchingdevicesforthefourmodesareshowninTable1.TheequivalentcircuitsofeachoperationstatesareshowninFigs.4-7.Fig.3illustratesthekeywaveformsoftheproposedconverter.Fortheanalysisofthisproposedconverter,thefollowingparametersaredefined:Fig.2.ForwardconverterwithproposeddemagnetizationcircuitNpNsLm=tiMl1Lml+Lm2Beforet=to,theswitchSisturnedoff.TheenergystoredinoutputinductanceLoiscontinuouslydeliveredto(2)(3)1391outputcapacitorCOandloadthroughrectifierdiodeD2.ThemagnetizingenergyisabsorbedbytheclampcapacitanceCc,thevoltageacrosscapacitorCc(vcc)isvcc.ThemagnetizingenergystoredintheclampcapacitorCcreleasetheenergytotheoutputbythewindingNp2andthediodeD4.Thus,theresonantvoltageacrossclampcapacitorCcandtheresonantcurrenticcaredecreased.ThemagnetizingcurrentiLmincreaseslinearlysincetheclampingcapacitorCcislargeenoughsothattheclampcapacitorvoltagevcccanbeapproximatedaconstant.Additional,becauseoftheclampcapacitorvoltagevccispositive,theprimarywindingvoltagev.ispositive.Also,thesecondarysidevoltageVsispositive,therectifierdiodeD1isturnedon,thediodeD2becomesoff.Therefore,theoutputcurrentflowsthroughtherectifierdiodeD1andstoresinoutputinductorLi,theoutputinductorcurrentiLisincreasing.Theprimarywindingvoltageandmagnetizingcurrentofthisstateareasfollows:mL)vP(t)=vc,(t)(l+Ll(4)Lm21LniLm(t)=iLm(to)+Lm(5)L_vcc(t)(I+I)(t-to)Lm2TheresonantvoltageandcurrentoftheclampcapacitorCcaregivenas:largerthanNvLmmVin+Vcc(to)coSCcI(t-to)VCc(t)=Lmm1r1243Fig.3.Thekeywaveformsofthecircuitoperationalmodefortheforwardconverterwithproposeddemagnetizationcircuit(6)iCC(t)=1D4(t)=-Vc(to)sincl(t-to)Zci(7)ThemainswitchcurrentiDSincludesthereflectedfilterinductorcurrentnDeviceSDID2D3D4CONDUCTIONSTATEOFSWITCHINGDEVICESUNDERFOuROPERATINGSTATES2134ateTABLEI,themagnetizingcurrentiLmandtheresonantclampcapacitorcurrenticc.From(5)and(7),themainswitchcurrentiDSisexpressedas:ONONOFFOFFON-ONONOFFOFFOFFOFFOFFONOFFOFFOFFONONOFFOFF'DS(t)=-+iLm(t)-icc(t)=nLmwhere+n+iLm(to)(8)Vc(t)(1+Lm2ml)(t-to)+s+incoc1(t-tto)ciqlState1(tot0):Thisstatestartsatt=to,whenmainswitchSisturnedonbythecontroller.ThediodesD1,D4areturnedon,thediodesD2,D3areturnedoff.Fig.4showstheequivalentcircuitofproposedconverterinthisstate.Inthisstate,themainswitchSisturnedon,thevoltageacrossswitchSiszero(VDs=0).DuetotheclampcapacitorvoltageVc,islargerthanP2Vin,themagnetizationinductancezccic-CCLeqlCC(9)(10)TO)cl2tVLeqlCC=(11)(12)Leql=LmlLm2L.ismagnetizedby1392Becauseofthemagnetizinginductanceislargeenough,themagnetizingcurrentiLmismuchsmallerthanthereflectedfilterinductorcurrentisabletoignore.Referringto(8),themaximumswitchcurrentofthisstateisgivenas:1DS-VcO+nThus,themagnetizingcurrentiLmWhenswitchSisturnedoffatt=t2,thisstateisfinished.State3(t2t3):Inthisstate,themainswitchSis-(to)(13)Thisstateendsattimet=t=-Twhentheresonantcurrenticc(t)reacheszero,thediodeD4becomesoff.TheresonantvoltageacrossclampingcapacitorCc,vCcisdroppedtoNNpviD4jASicTlDlD3+INPLmiiccccIN1NP2iDSNs12Iturnedoff.ThediodeD2isturnedon.ThediodesD1,D3andD4areturnedoff.Fig.6showstheequivalentcircuitofproposedconverterinthisstate.Duringthisstate,themostofmagnetizingenergystoredreleasetheclampcapacitorCc.TheswitchvoltageVDsislargerthanVi,(1+NP2)andtheFig.5.Theequivalentcircuitofstate2VinD404Lm2clampcapacitorvoltageVccislargerthanV,2V.The~~~CsFig.4.Theequivalentcircuitofstate1State2(tl4t2):Duringthisstate,themainswitchSremainsturn-onstate,thediodeD1isturnedon,thediodesD2,D3andD4areturnedoff.TheequivalentcircuitofthisstateisshowninFig.5.BecauseofthemainswitchSremainsonstate,thevoltageacrossthejunctioncapacitorCsiszeroTheprimarywindingvoltagevpequalstheinputThemagnetizationinductanceLmisvoltagevinmagnetizedandthemagnetizingcurrentincreaseslinearly.TheinputpowerisdeliveredtotheoutputthroughthetransformerT1.Thevoltageacrosstheclampcapacitanceprimarywindingvoltagevpandsecondarywindingvoltagevsarenegative,thesecondarysiderectifierdiodeD1becomesoff.TheoutputinductorcurrentiLisdecreasinglinearlyandcontinuestoflowindiodeD2.Inthisstate,theresonantcircuitincludestheswitchjunctioncapacitorCSQtheclampcapacitorCcandthemagnetizinginductance.Theswitchvoltageandthemagnetizingcurrentareexpressedas:VDS(t)=Vin+iLm(t4)Zc5sin(ic5(tht4)(16)iNp(t)=iLm(t)=LmLmVCC(t)=iLm(t4)Zc5Sinw(c5(t-t4)Lq5COS0(0c5(t-t4)Z5(17)(18)(19)(20)(21)(22)wherevccequalsv2VthecurrentflowsthroughtheclampZc5Ceq5thisstatearegivenas:capacitanceiCcdecreasetozero.ThesecondarysidevoltageVSisstillpositive,therectifierdiodesD1andD2maintainsrespectivelyonandoff.TheoutputinductorcurrentiLiscontinuouslyincreasinglinearly.ThefollowingequationsofiLm(t)=iLm(tl)+Lin(tmCeq5=CC+CrLeq5=Lml//Lm2Leq5Ceq5tl)Lm(14)(15)V)+-(t_tl)iNp(t)='DS(t)=-+iLm(t)-+iLm(tnnThisstateisendedwhenthemagnetizingcurrentiLmdecreasetozeroattimet=t3.Accordingto(17),themaximumvoltageacrosstheclampcapacitorCcandmain1393switchSareexpressedas:Vcc=iLm(t4)Zc5(1+Lm2)VDSmax=VDS(t5)=KVi+VCCCmxLmi=Vin+iLm(t4)Zc5(1+LmI)demagnetizationscheme.Componentvaluesandimportantparametersaredeterminedasfollows:1.MainswitchS:IRF02.SecondaryrectifiersD1,D2:SB16803.OutputInductorLO:2OuH4.Transformerturnratio:N1:N:NS=1:1:15.ClampingcapacitorCC:0.luF/500V6.D3,D4:UF1027.OutputcapacitorsCO:lOOOuF/1OV8.TransformermagnetizinginductanceLm1.2mH(Lm=Lml+Lm2)PRELIMINARYRESULTSAnexperimentalconverterwith1OOkHzswitchingfrequency,36-72Vinputvoltageand5V/1OAsingle-endedforwardconverterisdesignedtoverifytheproposedIII.Fig.6.Theequivalentcircuitofstate3State4(t3t4):Inthisstate,themainswitchSremainsturn-offstate.ThediodesD1andD2areturnedon.ThediodesD3andD4areturnedoff.Fig.7showstheequivalentcircuitofproposedconverterinthisstate.Att3,theswitchvoltageVDSreachesvi,,theprimarywindingvoltagev.andthesecondarywindingvoltageVSequalzeroduringthisstate.ThemagnetizingcurrentiLmremainsconstantbyflowingthroughtherectifierdiodeD1.SincethemagnetizingcurrentiLmismuchsmallerthanoutputcurrent,themostofoutputisprovidedbyoutputinductorcurrentiLflowsthroughdiodeD2.Thisstateisendedatt=t4whenthemainswitchSisturnedonbythecontroller.-Fig.8,Fig.9andFig.10showthesimulatedandexperimentalwaveformsoftheforwardconverterwithproposeddemagnetizationschemeatinputvoltageis48V,respectively.Thesimulatedandexperimentalwaveformsareverysimilartoeachother.Baseontheseresults,theycanbeusedtoverifythefeasibilityoftheproposeddemagnetizationscheme.InFig.11,comparedwithpowerconversionefficiencyoftheexperimentalforwardconverterwithtertiarytransformerwindingandproposeddemagnetizationcircuit,thereisnosignificantdifferenceintheefficiencyduringheavyloadcomparing.Thebestefficiencyisabout88%whiletheoutputis3Aforthesetwoways.IV.CONCLUSIONSThispaperpresentsanoveltransformercorerestschemeforsingle-endedforwardconverter.Withoutusingtheextratransformerwinding,thetransformerdemagnetizationcanbereachedbyaddingtwodiodesandaclampingcapacitor.Therefore,thetransformerwindingareacanbeimproved.Also,thewindingstructureofthetransformerissimplerthanthetransformerofthetertiarywindingresetforwardconverter.Furthermore,thetransformerdesignandPWMcontrolcircuitforthesingle-endedforwardconverterwithproposeddemagnetizationcircuitisthesameasconventionalforwardconverter.Theresultsoftheoperationalcircuitanalysis,computer-aidsimulation,andtheexperimentalhardwaremeasurementverifythefeasibilityoftheproposeddemagnetizationschemeforsingle-endedforwardconverter.ACKNOWLEDGMENTFig.7.Theequivalentcircuitofstate4TheauthorsgratefullyacknowledgefinancialsupportfromtheNationalScienceCouncilofTaiwanunderprojectNo.NSC95-2221-E-006-453-MY3.1394Vcc:5V/div||[1][2]ID1IDS.ivjV[3]VDS:50V/dV-[4]VGS:10OV/div_lsr,_~~~~~~~~~~~~~~2uS/di\\[5][6][7]Fig.8.Thesimulatedwaveformsoftheforwardconverterwithproposeddemagnetizationscheme..........[8][9]REFERENCESRudolfP.SevemsandGordon(Ed)Bloom,ModemDC-to-DCswitched-modepowerconversioncircuits,VanNostrandReinhold,1985.F.DongTan,\"Theforwardconverter:fromtheclasstothecontemporary,\"IEEEPESCRecord,2002,pp.857-863.RudySeverns,\"Thehistoryoftheforwardconverters,\"inSwitchingPowerMagazine,2000,vol.1,No.1,July,pp.20-22.AbrahamI.Pressman,SwitchingPowerSupplyDesign.Mc-Graw-HillCo.,2/e,1999.C.S.Leu,G.HuaandF.C.Lee,\"comparisonofforwardtopologieswithvariousresetschemes,\"Proc.VPECPowerElectronicSeminar,1991,pp.101109.C.S.Leu,G.HuaandF.C.Lee,\"AnalysisanddesignofR-C-Dclampforwardconverter,\"Proc.VPECPowerElectronicSeminar,1992,pp.113-120.NaokiMurakamiandMikioYamasaki,\"Analysisofaresonantresetconditionforasingle-endedforwardconverter,\"IEEEPESCRecord,1988,pp.1018-1023.J.A.Cobos,0.Garcia,J.SebastainandJ.Uceda,\"Resonantresetforwardtopologiesforlowoutputvoltageonboardconverters,\"IEEEAPECProceedings,1994,pp.1018-1023.M.Chen,D.XuandMikihikoMatsui,\"StudyonFig.9.TheexperimentalwaveformsoftheforwardconverterwithproposeddemagnetizationschemeCHI:VGS(IOV/div)CH2:VDs(50Vdiv)CH3:ID2(2A/div)[10][ii][12][13][14]Fig.10.TheexperimentalwaveformsoftheforwardconverterwithproposeddemagnetizationschemeCHI:VGS(lOV/div)CH2:VDs(50V/div)CH3:Icc(2A/div)CH4:magnetizinginductanceofhighfrequencytransformerinthetwo-transistorforwardconverter,\"PCCProceedings,2002,pp.597-602.J.Xu,X.CaoandQ.Luo,\"Animprovedtwo-transistorforwardconverter,\"IEEEPEDSProceedings,1999,pp.225-228.L.Qiong,F.C.LeeandM.M.Jovanovic,\"DesignconsiderationsoftransformerDCbiasofforwardconverterwithactive-clampreset,\"IEEEAPECProceedings,1999,pp.553-559.M.M.Jovanovic,M.T.ZhangandF.C.Lee,\"Evaluationofsynchronousrectificationefficiencyimprovementlimitsinforwardconverters,\"IEEETransactionIndustrialElectronics,Vol.42,pp.387-395,Aug.1995.K.C.TsengandT.J.Liang\"Novelhighefficiencystep-upconverter,\"IEEElectricPowerApplications,2004,vol.151,pp.182-190.T.J.LiangandK.C.Tseng,\"Analysisofintegratedboost-flybackstep-upconverter,\"IEEElectricPowerApplications,2005,vol.152,pp.217-225.Vcc(IOV/div)90-4-~~~For\\vardcnverterwthpropoeddem~ntizationcircuitForwardconverterxMthtertiarytrmnsformervning88-86-84-0g24.6,810I(A)FigI11.Powerconversionefficiencyoftheexperimentalforwardconverterwithtertiarytransformerwindingandproposeddemagnetizationcircuit1395
