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Switch-Mode Power Supplies Spice Simulations and Practical Designs.pdf

Switch-Mode Power Supplies Spic…

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2010-12-18 0人阅读 0 0 0 暂无简介 举报

简介:本文档为《Switch-Mode Power Supplies Spice Simulations and Practical Designspdf》,可适用于IT/计算机领域

INTRODUCTIONTOPOWERCONVERSIONUserfriendlinessisakeyfactorforthecommercialsuccessofanysimulationprogramThegrowingcomplexityofintegratedcircuitsandequipmentmakesthisaspectmoreandmoreimportantDespitenumerouspublicationsdevotedtotheSimulationProgramwithIntegratedCircuitEmphasis(SPICE),itstillscaresthenovicewhenitsnameismentionedDevelopedinthemidsbytheUniversityofCalifornia,Berkeley,theSPICEprogram’smainaimwastofulfilltheneedsoftheelectronicindustry––mainlyintegratedcircuitmakersHowever,withthesupportandfundsfromprivateeditors,theSPICEprogramhasevolvedoveranumberofyearsintomanypracticalandaffordablepackages,withemphasisonprovidingbothlowpricedandfriendlyaccesstobeginnersTheperformanceofSPICEcansignificantlyhelpyouspeedupthedesignphaseoftheequipmentyouarecurrentlyworkingon,evenifSPICEisnotabletogenerateanelectronicschematicbyitself!SPICEisinherentlyefficientbecauseifyoustartworkingwithanunfamiliarconcept,itwillquicklyenableyoutograspthefullmeaningofanyparticulararchitecturebyunveilingitspeculiarwaveformsYoucanthususethesimulatortogaininsightintothecircuityouhavetobuildandalsoensureallparametersaretakenintoaccountbeforethebreadboardphaseThisbookhasbeenwrittenforpowersupplydesigners,expertsintheirfields,butalsoforbeginnerswhowouldliketounderstandthesecretsofswitchmodepowerconversionManipulatingvirtualcomponentsonacomputerscreen,withoutthehazardofhighvoltage,offersaninterestingandsafewaytolearnthetechniqueFurthermore,the“experience”gainedinsimulation,anditisalsotrueforexpertssimulatinganovelconcept,willletyoufeelmorecomfortablewhenbreadboardingonthebench“DOYOUREALLYNEEDTOSIMULATE”HowmanytimeshaveyouheardthisquestionwhenaskingforasimulationpackageoranewcomputerThefollowingstatementsdonotrepresentanexhaustivelistofprosaboutcomputersimulation,buttheycancertainlybethoughtasa“helplist”availableduringthenegotiations:Hereisanargument:simulationcanavoidwasteoftimeandmoneyWithitsinherentiterativepower,SPICEcoversnumerousapplicationcasesinwhichyoucouldeasilydetectanydesignflaworproductweaknessThestabilityofaclosedloopSMPSrepresentsatypicalapplicationwhensomekeyfeedbackelementsaremoving(ie,thevariableloadthataffectsapole)orstarttodegradewithtemperatureandaging(astheelectrolyticequivalentseriesresistor)Moreover,designideascanalsobetestedorassessedinasnapshotthroughacomputerand,iftheyareworthtrying,furtherrefinedinthelabCHAPTERBassoCHqxd:PMPageDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteSource:SWITCHMODEPOWERSUPPLIESYoucanstarttoworkonaprojectbydownloadingcomponentsmodelsandbecomefamiliarwiththekeyelements,beforegoingtothebenchorwaitingforthesamplestobedeliveredOncetheyarrive,youwillhavealreadygainedinsightandthedebugphaseonthebenchwillclearlyhavebeenbeneficial!Simulatetestmeasurementswheneveryoudonotowntheadequateequipment:bandwidthmeasurementsrepresentagoodexampleIfyoucannotaffordanetworkanalyzer,thenaprovensmallsignalmodelcanstarttohelpyourefineyourfeedbackloopWhenrunonthefinalprototype,stabilityassessmentswillbefasterandmoreefficientPowerlibrariesaresafe:theyletyouexperiment“whatif”whenamperesandkilovoltsareflowinginthecircuitwithoutblowingupinthecaseofawrongconnection!Also,theyletyouseehowyourdesignreactstoashortcircuitoftheoptocoupler,ortheopeningofaresistorSPICEcanbegintogiveyoutheanswerWHATYOUWILLFINDINTHEFOLLOWINGPAGESThisbookthoroughlydetailstheadvantagesoftheSPICEpowertoletyouunderstand,simulate,test,andfinallyimprovetheswitchmodepowersupply(SMPS)youwanttodesignByprovidingyouwithspecificsimulationrecipes,thisworkintendstofacilitateasmuchaspossibleyourSMPSdesignUnlikeinotherbooks,theauthorhasstriventobalancethetheoreticalcontent,necessarytounderstandandquestionsimulationresults,andtheneedforpracticaldesignexamplesThisisdevelopedthroughouttheeightchaptersofthebookChapterexplainsswitchmodepowersupplytechniquesandtypesofconverters,anditintroducesafewimportantresultstohelpyoubetterunderstandaveragingtechniquesChapterexplainshowaveragemodelswerederived,anddifferenttypesaredescribedAgoodcomprehensionofthischapterisfundamental:itwillhelpyouquestioncertainweirdSPICEdata,resultingfromabadmodelimplementationIfyoudonotunderstandthewaythemodelhasbeenderived,youwillobviouslyfacesomedifficultiesinresolvingtheseissuesInChap,youwillalsolearnthewaytowireanaveragemodelandrunbasicsimulationsClosingtheloopisobviouslyanimportantaspectofconverterdesignandisoftenoverlookedThisisnotthecasehere,andChapwillguideyouthroughcontrolloopdesign,againusingpracticalexampleswithaTLandnotopampsonly,asoftenseenintheliteratureSincenoteveryintegratedcircuitalwayscomeswithaSPICEmodel,ChapdescribeshowthegenericswitchedmodelswerederivedThereadingofthischapterwillinterestthepersonwhowantstostrengthenherorhisknowledgeinSPICEmodelwritingChapterdescribespracticaldesignsofthethreebasicnonisolatedtopologies,includingthefrontendfilterBeforeanalyzingofflineconverters,ChapshowshowtodesigntherectifyingsectionandspendstimeonthevariouspowerfactorcorrectiontechniquesChapterisentirelydedicatedtotheflybackconverter,withspecificdesignexamplesattheendFinally,theforwardconverterappearsinChap,againassociatedwithadesignexampleWhenoneisdiscussingSPICEsimulations,oneofthegreatestissuesfindsitsrootintheversionsyntaxMostSPICEeditorsdealwithaproprietarysyntax,sometimesSPICEconformant,thatmakestranslationfromoneplatformtoanotheradifficultandpainfulexerciseToallowtheuseofdifferentsimulators,thestandardmodelspresentedthroughoutthepagesarecompatiblewithIntusoftIsSpice(SanPedro,Calif)andCADENCE’sPSpice(Irvine,Calif)Tohelpyouquicklycopyandpastetheexamples,wehaveincludedaCDROMinthisbookSomeselectedsimulationexamplesareofferedinIsSpiceandPSpicesyntax,andyoucaneasilyloadthemonyourcomputerifyouareequippedwithoneofthesesoftwareprogramsCHAPTERONEBassoCHqxd:PMPageDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteINTRODUCTIONTOPOWERCONVERSIONForstudentsornewcomerstotheSPICEworld,weaddthedemonstrationversionsoftheseeditorsTheyletyouopentheaforementionedfilesandsimulatesomeofthem(thosedemosaresizelimited)togiveyouatasteofwhatthefullversioncandoOtherdemonstrationversionsalsofindaplaceintheCDROM,suchasPSIM,Transim,Tina,Multisim,PowerBSpice,MicroCap,SpiceandTopSPICEForprofessionalpowersupplydesigners,anotherdiskisseparatelydistributedThisdiskcontainsthedesignexamplespresentedinthebookplusnumerousotherindustrialapplicationsusingrealcontrollersPleasevisittheauthor’swebsitefordistributiondetails(http:persoorangefrcbassoSpicehtm)WHATYOUWILLNOTFINDINTHISBOOKThisbookdoesnotdescribethewaySPICEoperates,nordoesitsolvetypicalelectriccircuitsItassumesthatthereaderisalreadyfamiliarwiththebasicsofSPICEsimulationsNumerousbooksandpapersareavailableonthesubjectasthegivenReferencessectiondetails,Wheneverpossible,theextendedbibliographywillguideyourchoiceifyouwishtostrengthenyourknowledgeinaparticulardomain,suchassometopologiesthatyouareunfamiliarwithIfsometheoreticalresultsaresometimesdeliveredjust“asis,”westronglyencouragethereadertodigfurtherintotheappropriateliteratureandacquirethetheorythatprecedestheresultThebookalsoonlyfocusesonasystemapproachNoSPICEdescriptionoftypicaldiscretepowerelementssuchasdiodes,MOSFETs,etc,isproposedFinally,hereistheimportantstatement,probablythemostinterestingone!SPICEdoesnotreplacethebreadboardphase,nordoesitshieldyoufromwritingequationsorunderstandingelectronicsItlookslikeasimplesentence,buttheauthorhasoftenbeenconfrontedbydesignersshowingboardsinthetrashandclaiming,“ButSPICEsaiditwouldwork!!”Yes,allideasworkonpaperuntiltheyfacethesolderingironcondemnationUseSPICEasadesigncompanion,acircuitinsiderthatcanrevealwaveformsdifficulttoobserveButalwaysquestionthedelivereddata:isthistherealbehavior,haveIbeenmisledsomewhere,doesasimplecalculationmoreorlessconfirmwhatIseeAfterthisbriefintroduction,itistimetoplungeintotheintricacyoftheSwitchModePowerSupplydesignandsimulationwithSPICECONVERTINGPOWERWITHRESISTORSIntheelectronicsworld,differenttypesofcircuitriesmustcohabit:logicdevices,analogcircuits,microprocessors,andsoonUnfortunatelyforthedesigner,thesecircuitsdonotcopewithasingle,fixed,powersupplyrail:amicroprocessororadigitalsignalprocessor(DSP)willneedastableVsourceorless,afrontendacquisitionboardwillrequire�VandperhapssomelogicgluearoundastandardVForthefinalboardbeingsuppliedfromasinglepowerpoint,eg,themainsoutletorabattery,howisonetoadaptanddistributeallthesedifferentvoltagestotheconcernedportionsThesolutionconsistsofinsertingasocalledconvertertoadaptthevoltagedistributiontothecircuitneedsAssociatingResistorsFigureportraysthesimplestoptionadesignercanthinkof:resistivedividers!IfourDSPconsumesmAoverV,thenitcanbereplacedbya�resistor,thesameasforourINTRODUCTIONTOPOWERCONVERSIONBassoCHqxd:PMPageDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteINTRODUCTIONTOPOWERCONVERSIONmA,Vlogiccircuitviathe�resistorFromaVsource,wecanthencalculatethedroppingresistors:()()Beforegoingfurther,pleasenotethatAorAwas,respectively,notedinthecalculationasmormThisisdonetoretaintheSPICEnotationforunits,withoutanyspaceItadherestothefollowingrulesandwillbeextensivelyusedintheremainingportionsofthebook:p�pico��n�nano��u�micro��m�milli��k�kilo�Meg�mega�•Bewarenottomixmegaandmilli,averycommonmistake:m��m,M��MegUnfortunately,theseresistorswillbetheseatofapermanentvoltagedrop,andpowerdissipation(inheat)willoccurThedissipatedpowerforeachresistoris(a)(b)Fromthesevalues,wecannowevaluatethesystemefficiencyobtainedbydividingthedeliveredoutputpowerPoutbythepowertakenawayfromthesourcePin:(a)(b)Pin�����m�m�WPout���m�m�mWP�(�)�mWP�(�)�mWR��m��R��m��CHAPTERONEFIGUREThesimplestvoltagedistributionviaresistorsRRloadVinVRRloadVlogicVDSPBassoCHqxd:PMPageDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteINTRODUCTIONTOPOWERCONVERSIONTheefficiency,representedbytheGreekletter�or“eta,”canbecomputedbydividingPoutbyPin,or()whichisanextremelypoorperformance!Theloss,dissipatedinheat,issimplythedifferencebetweenthepowerdeliveredbythesourceandthepower,convertedastherealwork,Pout()Inourexample,thelossis��mWAClosedLoopSystemIftheloadchanges,oriftheinputvoltagedrifts,whatisgoingtohappenWell,sinceourinputtooutputtransferratio,denotedM,isfixed,theoutputvoltagewillalsovaryTherefore,weneedtothinkofakindofregulatedsystemthatpermanentlyobservestheoutputpowerdemandandadjuststheseriesresistortomaintainaconstantoutputvoltage,iftheoutputvoltagerepresentsthevariableofinterestForawelldesignedsystem,theconvertermustalsoensureaproperregulationindependentlyfrominputvoltagevariationsToreachthisgoal,weneedtouseseveralparticularcomponentssuchas•AreferencevoltageVref:Thisvoltageisbydefinitionextremelystableintemperatureandpreciseinvalue(eg,�)Aprogrammableshuntregulator,suchasaTLadjustablezener,coulddothejob•Anoperationalamplifier(opamp):Thisdevicewillobserveaportionoftheoutputvoltage(�Vout)andcompareittothereferenceVrefItwillactually“amplify”theerror,thedifferencebetween�VoutandVref,todriveaseriespasselementTheerrormonitoredbytheopampisusuallydenominatedbytheGreeklettereor“epsilon”:•Aseriespasselement:ItcanbeaMOSFETorabipolartransistorbutworkinginalinearmode,playingtheroleofthenecessaryvariableresistorIfitisaMOSFET,thestaticdrivingpowerisForabipolar,thereisaneedtosupplyasufficientamountofbasecurrenttodelivertherightcollectororemittercurrentThisiscalledthebiascurrentFigurefinallyshowshowourresistiveconvertercouldbeimproved,let’ssayfortheVsectionTheerroramplifierismadeviaavoltagecontrolledvoltagesource(Eprimitive)andfeaturesagainofk(ordB)Oneofitsinputreceivesthevoltagereferencewhereastheotherone,theinvertinginput,isbiasedbyaportionoftheoutputvoltageThisisactuallyalinearregulator,however,limitedintheinputvoltagerangesinceVinshallbeaboveVoutbyaVbe,atleast,toguaranteeaproperdriveforQIfVoutisbelowthetarget(Vinourexample),EoutputincreasesandstrengthensQbiascurrent:VoutgoesupOntheotherhand,supposetheloadhassuddenlybeenreduced,thereforeVoutexceedsVThankstoE,Qbiascurrentgoesdown,reducingtheoutputvoltageuntilregulationismetagainTheoutputvoltageobservation,whichdelivers�Vout(afractionoftheoutputvoltage),isobtainedthrougharesistivedividermadeofRupperandRlowerCalculatingtheirvaluesisstraightforward:LetusfixacurrentcirculatinginthedividerbridgeSincethereisnobiasingcurrentforEintheexample(thisisthecaseformostMOSbasedtechnologies),wecouldtakeIb��A,forexampleAlowervalueisacceptable,butdegradesthenoiseimmunityinanoisyenvironmente�aVout�VrefPloss�Pin�Pout�Pout��Pout�Pouta��b��PoutPin���INTRODUCTIONTOPOWERCONVERSIONBassoCHqxd:PMPageDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteINTRODUCTIONTOPOWERCONVERSIONIbequals�AandentirelycirculatesinRlowerThankstothecontrolloop,Vis“seen”acrossRlowerTherefore,ThevoltagedropacrossRupperisVout�VrefThus,IfweneglectthepowerneededtodriveQ,thenallthesourcecurrentIinflowsintotheloadasIoutTherefore,applyingEq(),wecanderivetheefficiencyforthislinearregulator:()Ifwenowplottheefficiencyversustheinputvoltage,wecanseehowdifficultthesituationbecomesinthepresenceofsmallMratios(Fig)Forthesereasons,resistivedividertypeofconverters,thatistosayseriespassregulators,arelimitedtoapplicationwhereMdoesnotfallbelowOtherwisetheheatdissipationburdenshallbecomearealhandicapOnthe��PoutPin�VoutIoutVinIin<VoutVin�MRupper�Vout�VrefIb��u�k�Rlower�u�k�CHAPTERONEInputvoltage(V)Efficiency()FIGUREAssoonasMdiminishes,theefficiencydramaticallydrops(Vout�V)QNVinEkVrefRlowerkRupperkRloadIinIoutVoutIb––FIGURETheadditionofanerroramplifierbringsregulationtothecircuit:wehavebuiltalinearregulatorBassoCHqxd:PMPageDownloadedfromDigitalEngineeringLibraryMcGrawHill(wwwdigitalengineeringlibrarycom)Copyright©TheMcGrawHillCompaniesAllrightsreservedAnyuseissubjecttotheTermsofUseasgivenatthewebsiteINTRODUCTIONTOPOWERCONVERSIONotherhand,whentheuserreallyneedstooperatehisregulatortoratiosMcloserto(VinveryclosetoVout),thelowdropout(LDO)regulatormadewithaPNPbecomesagoodchoiceTheinputlowlimitisnowlinkedtothetransistorVce(sat)(afewhundredmillivolts,orless)ratherthanitsVbe(aroundmVatroomtemperature,C)Toclosethestudyonregulatorefficiency,wecantakethreedifferentoutputexampleswithlinearregulators,whereoutputandinputconditionsvary:Vin�VVout�VV�Vin�Vout�VVin�VVout�VV�Vin�Vout�VVin�VVout�VV�Vin�Vout�VAsaresult,onecanseethatahighefficiencycanbeobtainedwithalinearregulatorifVissmall(asplottedinFig),butalsoifVout��VDerivingUsefulEquationswiththeLinearRegulatorFigureisinterestingbecausewecanuseittoderivegeneralstatements,pertinenttotheclosedloopworldwearegoingtoenter,linear,orswitchedSupposethatweremovetheerroramplifierandreplaceitbyafixedvoltagesourceofV,ouractualopampoutput(lookatFigvalues)asFigashowsTheregulatorbecomesasimpleemitterfollowercircuit,affectedbyanoutputimpedanceandanoutputvoltageAssuch,itcanbedescribedwithitsequivalentThéveningenerator,whatFigbsuggestsRs,OLrepresentstheopenloopoutputimpedanceandVth,thevoltagedeliveredwhenbiasedbyacontrolvoltageVc,ourfixedVintheapplicationLetusnowusethisrepresentationandredrawourclosedloopregulatoraroundit,ignoring,fornow,theinputvoltagecontribution:InFig,Vout(s)iscomparedtoVref(s)viaaresistivedivideraffectedbyatransferratioof�

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