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1、DesignandAnalysisonReducedSwitchingFrequencyCurrentModeControlIsolatedPowerConvertersforLightLoadEfficiencyYuRuiyangM.H.PongUniversityofHongKongSeniorMember,IEEEDepartmentofEEE,UniversityofHongKongyry721@eee.hku.hkDepartmentofEEE,mhp@eee.hku.hkAbstract–Thispaperfocusonimprov
2、inglightloadefficiencyofisolatedDC/DCconverters.Amixedsignalcontrolplatformisproposedtoimplementmultiple-modevariablefrequencycontrol.An8-bitMicroControllerUnitMCUisusedintheplatformtoprovideadaptivecontrolschemesandcosteffectivenessdigitalsolutions.Smallsignalanalysisiscove
3、redtoexplainfrequencymodulationeffects.Controlofisolationtransformerfluxswingtoavoidsaturationisalsoimplemented,toprovidesafeoperationbothinsteadyandtransientstates.A300WattprototypeTwo-FETforwardconverterisbuiltuptoverifytheproposedmixedsignalcontrolplatform.IndexTerms—Isol
4、atedDC/DCconverters,MultipleModes,LightLoadEfficiency,PulseFrequencyModulationPFM,MixedSignalControl.I.INTRODUCTIONMostofelectronicdevicesoperateatlightloadconditionsformostofthetime,forexample,printers,adapters,LCDTVsanddesktopPCs.Thus,lightloadefficiencybecomesamajorconcer
5、ninswitchmodepowersupplydesignstage.Figure1AmixedsignalPlatformforvariablefrequencyReducingswitchingfrequencyisapopularmethodtoControlincreaselightloadefficiency.Inordertohavegoodperformanceoverawiderangeofload,multiple-modesareoftenimplementedinthepowerconverter,fromstandby
6、II.STEADYSTATEANALYSISburstmode(Below1%ratedload),lightload(1%to20%ratedload)tofullload.A.OperatingProfileLotsofcontrolmethodswereimplementedinbuckInconventionalfixedfrequencypeakcurrentmodeconvertertoboostupthelightloadefficiency[1-6].Thereareconverter,theswitchingfrequency
7、iskeptasaconstantvalue.somecommercializedICs[7-9]toimplementthesefunctionsInordertoboostuplightloadefficiency,switchingfrequencyonDC/DCisolatedflybackconverters.However,flybackneedstobereducedatlightloadcondition.Fig.1showsanconvertersonlyapplysmallpowerconversionapplication
8、s.isolatedDC/DCconverterwithmultiplemodes.Atlightload,Inthispaper,wefocuson
