外文翻译开关模式电源.docx

外文翻译开关模式电源.docx

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外文翻译开关模式电源

中文4060字

外文文献

Switched-modepowersupply

Aswitched-modepowersupply（alsoswitching-modepowersupply,SMPS,orsimplyswitcher）isanelectronicpowersupplyunit（PSU）thatincorporatesaswitchingregulator.Whilealinearregulatormaintainsthedesiredoutputvoltagebydissipatingexcesspowerinapasspowertransistor,theswitched-modepowersupplyswitchesapowertransistorbetweensaturation（fullon）andcutoff（completelyoff）withavariabledutycyclewhoseaverageisthedesiredoutputvoltage.Itswitchesatamuch-higherfrequency（tenstohundredsofkHz）thanthatoftheACline（mains）,whichmeansthatthetransformerthatitfeedscanbemuchsmallerthanoneconnecteddirectlytotheline/mains.Switchingcreatesarectangularwaveformthattypicallygoestotheprimaryofthetransformer;typicallyseveralsecondariesfeedrectifiers,seriesinductors,andfiltercapacitorstoprovidevariousDCoutputswithlowripple.

Themainadvantageofthismethodisgreaterefficiencybecausetheswitchingtransistordissipateslittlepowerinthesaturatedstateandtheoffstatecomparedtothesemiconductingstate（activeregion）.Otheradvantagesincludesmallersizeandlighterweight（fromtheeliminationoflowfrequencytransformerswhichhaveahighweight）andlowerheatgenerationduetohigherefficiency.Disadvantagesincludegreatercomplexity,thegenerationofhighamplitude,highfrequencyenergythatthelow-passfiltermustblocktoavoidelectromagneticinterference（EMI）,andaripplevoltageattheswitchingfrequencyandtheharmonicfrequenciesthereof.

Anoteaboutterminology

Althoughtheterm"powersupply"hasbeeninusesinceradioswerefirstpoweredfromtheline/mains,thatdoesnotmeanthatitisasourceofpower,inthesensethatabatteryprovidespower.Itissimplyadevicethat（usually）acceptscommercialACpowerandprovidesoneormoreDCoutputs.Itwouldbemorecorrectlyreferredtoasapowerconverter,butlongusagehasestablishedtheterm.

Classification

SMPScanbeclassifiedintofourtypesaccordingtotheinputandoutputwaveforms:

ACin,DCout:

rectifier,off-lineconverterinputstage

DCin,DCout:

voltageconverter,orcurrentconverter,orDCtoDCconverter

ACin,ACout:

frequencychanger,cycloconverter,transformer

DCin,ACout:

inverter

Inputrectifierstage

IftheSMPShasanACinput,thenthefirststageistoconverttheinputtoDC.Thisiscalledrectification.Therectifiercircuitcanbeconfiguredasavoltagedoublerbytheadditionofaswitchoperatedeithermanuallyorautomatically.Thisisafeatureoflargersuppliestopermitoperationfromnominally120voltor240voltsupplies.TherectifierproducesanunregulatedDCvoltagewhichisthensenttoalargefiltercapacitor.ThecurrentdrawnfromthemainssupplybythisrectifiercircuitoccursinshortpulsesaroundtheACvoltagepeaks.Thesepulseshavesignificanthighfrequencyenergywhichreducesthepowerfactor.SpecialcontroltechniquescanbeemployedbythefollowingSMPStoforcetheaverageinputcurrenttofollowthesinusoidalshapeoftheACinputvoltagethusthedesignershouldtrycorrectingthepowerfactor.AnSMPSwithaDCinputdoesnotrequirethisstage.AnSMPSdesignedforACinputcanoftenberunfromaDCsupply（for230VACthiswouldbe330VDC）,astheDCpassesthroughtherectifierstageunchanged.It'showeveradvisabletoconsultthemanualbeforetryingthis,thoughmostsuppliesarequitecapableofsuchoperationeventhoughnothingismentionedinthedocumentation.However,thistypeofusemaybeharmfultotherectifierstageasitwillonlyutilizehalfofdiodesintherectifierforthefullload.Thismayresultinoverheatingofthesecomponents,andcausethemtofailprematurely.

Ifaninputrangeswitchisused,therectifierstageisusuallyconfiguredtooperateasavoltagedoublerwhenoperatingonthelowvoltage（~120VAC）rangeandasastraightrectifierwhenoperatingonthehighvoltage（~240VAC）range.Ifaninputrangeswitchisnotused,thenafull-waverectifierisusuallyusedandthedownstreaminverterstageissimplydesignedtobeflexibleenoughtoacceptthewiderangeofdcvoltagesthatwillbeproducedbytherectifierstage.Inhigher-powerSMPSs,someformofautomaticrangeswitchingmaybeused.

Inverterstage

TheinverterstageconvertsDC,whetherdirectlyfromtheinputorfromtherectifierstagedescribedabove,toACbyrunningitthroughapoweroscillator,whoseoutputtransformerisverysmallwithfewwindingsatafrequencyoftensorhundredsofkilohertz（kHz）.Thefrequencyisusuallychosentobeabove20kHz,tomakeitinaudibletohumans.Theoutputvoltageisopticallycoupledtotheinputandthusverytightlycontrolled.Theswitchingisimplementedasamultistage（toachievehighgain）MOSFETamplifier.MOSFETsare