开关电源经典分析ppt课件.ppt

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1、ForwardConverterBECKContentsBasicResonantresetRCDclampLCDsnubberresetActiveclampresetDualswitchforwardconverter1.BasicDerivedfrombuckconverterFeaturesthesameasthoseofbuckconverterVolt-secondproductbalanceNecessaryVrsetcanbeobtainedbydifferentresetschemesresetwithterti

2、arywindingresonantresetRCD-clampresetLCDresetactive-clampresetHighvoltagestressonQForNc=Np,VDS(max)=2VINLeakageinductanceoftransformerfurtherincreasesvoltagestressonprimaryswitchResonantResetForwardNoexternalresetcircuitrequiredCstotalcapacitanceacrossswitch(Coss+exte

3、rnalcapacitance,ifany)minimumcomponentcount2.ResonantResetDesignGuideline設計概要LMenergywillbetransferredtoCrtotallyduringresettimeLMresonantwithCr,theresonantperiodeffectstheresettimeandthereforethemaximumdutycycleHighCrwillresultin:highswitchingonlossandlongresettimelo

4、wturningofflossForwideinputvoltage,Dmaxcanbesethighas0.6DesignEquationsFeatures:Resetdependentonswitchparasiticcomponent,I.e.,outputcapacitanceCossRelativelyhighpeakresetvoltage:typical2Vin,maxMagnetizingenergyofthetransformerrecycledtotallyApplicationswithrelativelyl

5、owinputvoltage:lowcostandhighefficiency3.RCD-ClampResetRCD-ClampforwardconverterClampVoltageCompletetransformerresetwhenDmax@lowVinVc>nVo1-DmaxPeaktransistorandrectifierdiodevoltageVDS=Vin,max+VcVD1=VcnClampResistorClampNetworkDesignFeaturesAdvantageofRCD-clampreset:S

6、implecircuitandlowcostLimitationsofRCD-clampreset:doesnotrecyclesmagnetizingenergydoesnorutilizesentireoff-timeforreset(largedeadtime)Suitableforapplicationoflowpowerandlowvoltageoutput4.LCD-SnubberResetLCDsnubberresetforwardconverterTheoreticallyrecyclespartofmagneti

7、zingenergyPractically,recycledenergyminimalDesignGuidelineLMenergy,alsowithleakageinductanceenergy,willbetransferredtoCstotallyduringresettimeLMresonantwithCs,theresonantperiodeffectstheresettimeandthereforethemaximumdutycycleHighCswillresultin:lowVDS,max,softturnofft

8、huslowswitchingofflossandlongresettimeResonantperiodofCsandLsshouldshorterenoughthantheDminTsFordampingtheresonanceofLsandC1