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1、ArticleinWileyEncyclopediaofElectricalandElectronicsEngineeringDC-DCPowerConvertersRobertW.EricksonDepartmentofElectricalandComputerEngineeringUniversityofColoradoBoulder,CO80309-0425Dc-dcpowerconvertersareemployedinavarietyofapplications,includingpowersuppli
2、esforpersonalcomputers,officeequipment,spacecraftpowersystems,laptopcomputers,andtelecommunicationsequipment,aswellasdcmotordrives.Theinputtoadc-dcconverterisanunregulateddcvoltageVg.TheconverterproducesaregulatedoutputvoltageV,havinga1++Lmagnitude(andpossibl
3、ypolarity)that2Vg+vs(t)CRVdiffersfromVg.Forexample,ina–computeroff-linepowersupply,the––120Vor240VacutilityvoltageisDcLoadinputSwitchnetworkLow-passfilterDcoutputrectified,producingadcvoltageof(a)approximately170Vor340V,respectively.Adc-dcconverterthenreduces
4、thevoltagetotheregulated5Vvs(t)Vgor3.3VrequiredbytheprocessorICs.V=DVsgHighefficiencyisinvariablyrequired,sincecoolingofinefficient0DTs(1–D)TstpowerconvertersisdifficultandSwitchexpensive.Theidealdc-dcconverterposition:121exhibits100%efficiency;inpractice,(b)
5、Figure1.Thebuckconverterconsistsofaswitchnetworkthatefficienciesof70%to95%arereducesthedccomponentofvoltage,andalow-passfilterthatremovesthehigh-frequencyswitchingharmonics:(a)typicallyobtained.Thisisachievedschematic,(b)switchvoltagewaveform.usingswitched-mo
6、de,orchopper,circuitswhoseelementsdissipatenegligiblepower.Pulse-widthmodulation(PWM)allowscontrolandregulationofthetotaloutputvoltage.Thisapproachisalsoemployedinapplicationsinvolvingalternatingcurrent,includinghigh-efficiencydc-acpowerconverters(invertersan
7、dpoweramplifiers),ac-acpowerconverters,andsomeac-dcpowerconverters(low-harmonicrectifiers).Abasicdc-dcconvertercircuitknownasthebuckconverterisillustratedinFig.1.Asingle-poledouble-throw(SPDT)switchisconnectedtothedcinputvoltageVgasshown.Theswitchoutputvoltag
8、evs(t)isequaltoVgwhentheswitchisinposition1,andisequaltozerowhentheswitchisinposition2.Theswitchpositionisvariesperiodically,suchthatvs(t)isarectangularwaveformhavingperiodTsanddutycycleD