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1、IEEETRANSACTIONSONPOWERELECTRONICS,VOL.27,NO.4,APRIL20122153NovelSelf-ConfigurableCurrent-MirrorTechniquesforReducingCurrentImbalanceinParallelLight-EmittingDiode(LED)StringsSiNanLi,W.X.Zhong,WuChen,Member,IEEE,andS.Y.R.Hui,Fellow,IEEEAbstractTraditionalcurrent-mirrormethodsrequireo
2、nefixedcurrentreferenceforcontrollingothercurrentsourceorsources.Inthispaper,anewself-configurablecurrent-mirrormethodthatcandynamicallydeterminethebestcurrentbranchasthecur-rentreferenceinordertoensuregoodbalanceofallparallelcurrentsourcesisproposed.Theoperatingprincipleinvolvesadyn
3、amicandself-configurabletransistor-basedcurrent-balancingcircuitthatcanbeoperatedinsaturationorlinearmode.Inei-theroperatingmode,goodcurrentbalanceorsharingamongallparallel-connectedcurrentsourcescanbeguaranteed.Thenovelcurrent-balancingcircuitdoesnotrequireaseparatepowersupplyforpo
4、weringtheircontrolcircuits.Theproposalisamodularonethatcanbeexpandedtoanynumberofparallelcurrentsources.ItsprinciplehasbeensuccessfullyappliedtocurrentbalancingofparallelLEDstrings.IndexTermsCurrentbalance,currentmirrors,LED.Fig.1.CMcircuitforbalancingcurrentsinparallelLEDstrings[2
5、].I.INTRODUCTIONURRENTimbalanceproblemsinparallelLEDstringsChaveattractedmuchattentioninrecentyearsasLEDtech-nologyisperceivedasanemergingtechnologyforreplacingincandescentandfluorescentlamps.Useofseries-connectedLEDpackagesrequiresahighvoltagepowersupplyandsoparallelarrangementsofL
6、EDstringsarecommonpracticepar-ticularlyinmedium-andhigh-powerLEDsystems.However,ithasbeenpointedout[1]that,duetothevariationsofLEDpackages,evenasmallmismatchof0.42VamongparallelLEDstringscouldleadtosignificantcurrentimbalanceandreductionofsystemreliabilityandlifetime.Tocopewiththecu
7、rrentimbalanceprobleminparallel-connectedLEDstrings,researchershaveproposedvariousmethods.ForparallelLEDstringsdrivenbyacommondccurrentsource,thesimplestbuthighlyinefficientmethodistohaveacurrent-balanceresistorinFig.2.PreviousproposalofcurrentbalancingofLEDstringsusinglinearcurrent
8、regulatorspoweredbyasepara
