开关电源中的磁性元件

MagneticsinSwitched-ModePowerSuppliesOutlineBlockDiagramofaTypicalAC-DCPowerSupplySpecificationofthePowerSupplyKeyMagneticElementsinaPowerSupplyReviewofMagneticConceptsMagneticMaterialsInductorsandTransformersReferencesBlockDiagramofanAC-DCPowerSupplyInputFilterRectifierPFCPowerStageTrans-FormerOutputCircuitsACInputDCOutputs(toloads)Specifications(Abbreviated)100-WattThree-OutputPowerSupply1003InputVoltage:90–264Vac,47-63Hz90264V4763HzInputCurrent:2Amaximum.2AInputHarmonics:MeetsIEC1000-3-2A14forallloadconditions.IEC1000-3-2A14Hold-upTime:20msminimum.20msInrushCurrent:40Apeakat264V(coldstart)264V40AOutputs:MIN.MAX.51.510502.0%3.30.35502.0%120.331002.0%OUTPUTVOLTAGE(V)(v)OUTPUTCURRENT(A)(v)RIPPLE(mVpp)(mVpp)TOTALREGULATIONSpecifications(cont’d.)Efficiency:75%minimumatfullload,120Vacinput120V75Temperature:Operating:Seederatingcurvebelow–Storage-40oCto+85oC-40oC+85oCTemperatureDerating100W80W40oC60oC20oC0oC70oC50oC10oC30oC200LFMFORCEDAIRCOOLINGNATURALCONVECTIONCOOLING50W40W200LFMFunctionalBlockDiagramNGLPFCControl+Bus+BusReturn5V,10A3.3V,5AMagAmpReset12V,3A-+++--PWMControl+Bus++BusReturnInputFilterRectifierPFCPowerStageOutputCircuitsXfmrPFCControPFCl+BusReturnBUSPWMControlPWM+BusReturn+MagAmpReset+Bus+TransformerInforwardconverters,asinmosttopologies,thetransformersimplytransmitsenergyfromprimarytosecondary,withnointentofenergystorage.Coreareamustsupporttheflux,andwindowareamustaccommodatethecurrent.=Areaproduct.=AP5V,10A12V,3A++--Xfmr+BusReturn++Bus+Q2L3aCR2CR3CR4CR5L3bC5C6OutputCircuitsPopularconfigurationforthesevoltages---twosecondaries,withalowervoltageoutputderivedfromthe5Voutputusingamagamppostregulator.——5VFeedbacktoprimaryPWMisusuallyfromthe5Voutput,leavingthe+12Voutputquasi-regulated.PWM5V12V5V,10A3.3V,5AMagAmpReset12V,3A-+++--From12VsecondaryFrom5VsecondaryCR3CR4C7CR2CR5CR7C6L3aCR6C5L3bL4CR8SR112V15VMagAmpResetLeakageCurrentisAffectedbytheTransformerWithoutinsulationintheappliance,theuserprovidesapathfortheelectricalcurrenttoreturntoground!Evenwithinsulation,somesmallleakagecurrentflows.Thedottedlineshowsthe“thirdwire”ground,notpresentin2-wire(“Class2”)appliances.“”2“2”Leakagecurrentspecificationsinfluencethedesignoftheinputfilter,asthebypass(“Y”)capacitorsconductcurrentfromthelinetoground.“Y”PowerBox(circuitbreakers)120VacGroundVictimNurse(CPRTrained)CPRPowerFromUtilityTransformer(cont’d)Notethepolaritydots.–OutputsconductwhileQ2ison.Q2–SecondaryVpeaks=+Bus•Ns/NpVpeaks=+Bus•Ns/NpNotethecoupledoutputchoke,L3.L3–Windingsmusthavesameturnsratiosastransformer,whichisthesameasoutputvoltagesplusdiodedropsofCR3andCR5.–CR3CR5Withoutputchokesincontinuousconduction,eachoutputvoltageistheaverageofitssecondaryvoltage(neglectingdiodedrops).Therefore,eachoutputvoltageisitssecondarypeakvoltagetimesthedutyratiooftheprimarybusvoltage,+Bus,(neglectingdiodedropsandQ2’sONvoltage).BusQ25V,10A12V,3A++--Xfmr+BusReturn+BusQ2L3aCR2CR3CR4CR5L3bC5C6ReviewofSomeMagneticConceptsUnitsusedinthedesignofmagneticcomponentsCurrentandmagneticfluxCharacteristicsofmagneticmaterialsFaraday’sLaw(the“transformerequation”)“”UnitsandTheirSymbolsNote:Unitsnamedforfamouspeoplearenotcapitalized(ampere,henry,volt),buttheirsymbolsare(A,H,V).amperehenryvoltAHVSymbolDescriptionSIUnitsSIHfieldstrengthA-t/mBfluxdensitytesla(T)µPermeabilityT-m/A-t2FmagnetomotiveforceA-tφFluxweber/t/t(Wb/t)RReluctanceA-t2/WbPPermeancehenry/t2/t2ICurrentampere(A)LInductancehenry(H)Nwindingturnsturn(t)Right-HandRuleFluxDirectionasaResultofCurrentFlowWrapone’srighthandaroundaconductorwiththumbpointinginthedirectionofcurrentflow.Fingerspointinthedirectionoffluxlines.MaterialCharacteristicsBulkpropertyofthematerialH=NI/le=ampere⋅turnspermeterH=NI/le=–Classicdefinitionisamperespermeter(assumesonlyoneturn)–le=magneticpathlengthle=µ=permeability,usuallyrelativetoair(µair=4⋅π⋅10-7H/m)µ=µ=4⋅π⋅10-7H/mBfluxdensityintesla(1tesla=10,000gauss)Hmagneticfieldstrengthinampereturns/meterSlope=B/H=µ=permeabilityAirµ(relative)=1B/Hµ1=10,000/µ=1CoreCharacteristicsCorewithnowinding.Materialcharacteristics,withAeandleadded.Aele–Ae=corearea,le=effectivemagneticpathlengthAe=le=–Commonunitfortheslopeis“InductanceFactor,”usuallygiveninnH/t2“”nH/t2F=Hlemagnetomotiveforceinampereturnsφ=BAefluxinwebers(1weber=1teslasquaremeter)Slope=φ/F=P=permeanceInductanceFactorinH/t2=φ/F=P“”H/t21=1·2WoundCoilCharacteristicsUsingvolt-secondsandamperes,thewoundcomponentcanbeanalyzedeasilybycircuitengineersusingtime-domainanalysis.·IcurrentinamperesΝφfluxturnsinweberturns=voltsecondsSlope=L=inductance(henries)L=·The“TransformerEquation”“”(Faraday’sLaw)Bintesla,Aeinm2,finHzBAem2fHz–ModernSIunitsSIThesaturationfluxdensity,Bmax,determinesthemaximumvoltsperturnthatcanbeappliedtoagiventransformerorinductorwindingatagivenfrequency.BmaxfABNEe⋅⋅=4Watchclosely,now:TransformerEquationfromFaraday’sLawNote:Thisappliestosquarewaves(where∆t=halfoftheperiod).∆t=B∆BtNE∆∆Φ=eAB⋅=ΦfTt12121⋅==∆eeABAB⋅=⋅∆=∆Φ2fABABtNEefe⋅⋅=⋅⋅=∆∆Φ=41221AnExtremelyImportantFactUnlessthefluxischanging,therewillbenovoltage.Ifthefluxswingsbackandforth,sowil