电气毕业设计 英文翻译Word文档下载推荐.docx

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scheduledtoenterproduction.

Thistypeofsituationcanleadtothe“millstoneeffect”whichinsimpletermsmeans“Youdesignedit,youfixit（forever）.”Nowondernoonewantstotouchitand,whenasked,disavowsanyknowledgeofhavingeverdesignedapowersupply.

1.1GettingStarted.ThisJourneyStartswiththeFirstQuestion

Inordertoproduceagooddesign,manyquestionsmustbeaskedpriortothebeginningofthedesignprocess.Theearliertheyareaskedthebetteroffyouare.Thesequestionsalsoavoidmanyproblemslaterinthedesignprogramduetolackofcommunicationandforethought.Thebasicquestionstobeaskedincludethefollowing.

Fromthemarketingdepartment

1.Fromwhatpowersourcemustthesystemdrawitspower?

Therearedifferentdesignapproachesforeachpowersystemandonecanalsogetinformationastowhatadverseoperatingconditionsareexperiencedforeach.

2.Whatsafetyandradiofrequencyinterferenceandelectromagneticinterference（RFI/EMI）regulationsmustthesystemmeettobeabletobesoldintothetargetmarket?

Thiswouldaffectnotonlytheelectricaldesignbutalsothephysicaldesign.

3.Whatisthemaintenancephilosophyofthesystem?

Thisdictateswhatsortofprotectionschemesandphysicaldesignwouldmatchtheapplication.

4.Whataretheenvironmentalconditionsinwhichtheproductmustoperate?

Thesearetemperaturerange,ambientRFlevels,dust,dirt,shock,vibration,andanyotherphysicalconsiderations.

5.Whattypeofgracefuldegradationofproductperformanceisdesiredwhenportionsoftheproductfail?

Thiswoulddeterminethetypeofpowerbusingschemeandpowersequencingthatmaybenecessarywithinthesystem.

Fromthedesignersoftheotherareasoftheproduct

1.Whatarethetechnologiesoftheintegratedcircuitsthatarebeingusedwithinthedesignofthesystem?

Onecannotprotectsomething,ifonedoesn’tknowhowitbreaks.

2.Whatarethe“bestguess”maximumandminimumlimitsoftheloadcurrentandarethereanyintermittentcharacteristicsinitscurrentdemandsuchasthosepresentedbymotors,videomonitors,pulsedloads,andsoforth?

Alwaysadd50percentmoretowhatistoldtoyousincetheseestimatesalwaysturnouttobelow.Alsowhatarethemaximumexcursionsinsupplyvoltagethatthedesignerfeelsthatthecircuitcanwithstand.Thisdictatesthedesignapproachesofthecross-regulationoftheoutputs,andfeedbackcompensationinordertoprovidetheneedsoftheloads.

3.Arethereanycircuitsthatareparticularlynoise-sensitive?

Theseincludeanalog-to-digitalanddigital-to-analogconverters,videomonitors,etc.Thismaydictatethatthesupplyhasadditionalfilteringormayneedtobesynchronizedtothesensitivecircuit.

4.Arethereanyspecialrequirementsofpowersequencingthatarenecessaryforeachrespectivecircuittooperatereliably?

5.Howmuchphysicalspaceandwhatshapeisallocatedforthepowersupplywithintheenclosure?

Itisalwaystoosmall,sostartnegotiatingforyourfairshare.

6.Arethereanyspecialinterfacesrequiredofthepowersupply?

Thiswouldbeanypower-downinterrupts,etc.,thatmayberequiredbyanyoftheproduct’scircuits.

Thisinquisitivenessalsosetsthestageforthebeginningofthedesignbydefiningtheenvironmentinwhichthepowersupplymustoperate.Thisthenformsthebasisofthedesignspecificationofthepowersupply.

1.2PowerSystemOrganization

Theorganizationofthepowersystemwithinthefinalproductshouldcomplementtheproductphilosophy.Thegoalofthepowersystemistodistributepowereffectivelytoeachsectionoftheentireproductandtodoitinafashionthatmeetstheneedsofeachsubsectionwithintheproduct.Toaccomplishthis,oneormorepowersystemorganizationcanbeusedwithintheproduct.

Forproductsthatarecomposedofonefunctional“module”thatisinseparableduringtheproduct’slife,suchasacellulartelephone,CRTmonitor,RFreceiver,etc.,anintegratedpowersystemisthetraditionalsystemorganization.Here,theproducthasonemainpowersupplywhichiscompletelyself-containedandoutputsdirectlytotheproduct’scircuits.Anintegratedpowersystemmayactuallyhavemorethanonepowersupplywithinitifoneoftheloadcircuitshaspowerdemandorsequencingrequirementswhichcannotbeaccommodatedbythemainpowersupplywithoutcompromisingitsoperation.

Forthoseproductsthathavemanydiversemodulesthatcanbereconfiguredoverthelifeoftheproduct,suchasPCBcardcagesystemsandcellulartelephonegroundstations,etc.,thenthedistributedpowersystemismoreappropriate.Thistypeofsystemtypicallyhasonemain“bulk”powersupplythatprovidespowertoabuswhichisdistributedthroughouttheentireproduct.Thepowerneedsofanyonemodulewithinthesystemareprovidedbysmaller,board-levelregulators.Here,voltagedropsexperiencedacrossconnectorsandwiringwithinthesystemdonotbotherthecircuits.

Theintegratedpowersystemisinherentlymoreefficient（lesslosses）.Thedistributedsystemhastwoormorepowersuppliesinseries,wheretheoverallpowersystemefficiencyistheproductoftheefficienciesofthetwopowersupplies.So,forexample,two80percentefficientpowersuppliesinseriesproducesanoverallsystemefficiencyof64percent.

Thetypicalpowersystemcanusuallyendupbeingacombinationofthetwosystemsandcanuseswitchingandlinearpowersupplies.

Theengineer’smottotolifeis“Lifeisatradeoff”anditcomesintoplayhere.Itisimpossibletodesignapowersupplysystemthatmeetsalltherequirementsthatareinitiallysetoutbytheotherengineersandmanagementandkeepitwithincost,space,andweightlimits.Thetypicalinitialrequirementofapowersupplyistoprovideinfinitelyadaptablefunctions,deliverkilowattswithinzerospace,andcostnomoney.Obviously,somecompromiseisinorder.

1.3SelectingtheAppropriatePowerSupplyTechnology

Oncethepowersupplysystemorganizationhasbeenestablished,thedesignerthenneedstoselectthetechnologyofeachofthepowersupplieswithinthesystem.Attheearlystageofthedesignprogram,thisprocessmaybeiterativebetweenreorganizingthesystemandthechoiceofpowersupplytechnologies.Theimportantissuesthatinfluencethisstageofthedesignare:

1.Cost.

2.Weightandspace.

3.Howmuchheatcanbegeneratedwithintheproduct.

4.Theinputpowersource（s）.

5.Thenoisetoleranceoftheloadcircuits.

6.Batterylife（iftheproductistobeportable）.

7.Thenumberofoutputvoltagesrequiredandtheirparticularcharacteristics.

8.Thetimetomarkettheproduct.

Thethreemajorpowersupplytechnologiesthatcanbeconsideredwithinapowersupplysystemare:

1.Linearregulators.

2.Pulsewidthmodulated（PWM）switchingpowersupplies.

3.Highefficiencyresonanttechnologyswitchingpowersupplies.

Eachofthesetechnologiesexcelsinoneormoreofthesystemconsiderationsmentionedaboveandmustbeweighedagainsttheotherconsiderationstodeterminetheoptimummixtureoftechnologiesthatmeettheneedsofthefinalproduct.Thepowersupplyindustryhaschosentoutilizeeachofthetechnologieswithincertainareasofproductapplicationsasdetailedinthefollowing.

Linear

Linearregulatorsareusedpredominantlyinground-basedequipmentswherethegenerationofheatandlowefficiencyarenotofmajorconcernandalsowherelowcostandashortdesignperiodaredesired.Theyareverypopularasboardlevelregulatorsindistributedpowersystemswherethedistributedvoltageislessthan40VDC.Foroff-line（plugintothewall）products,apowersupplystageaheadofthelinearregulatormustbeprovidedforsafetyinordertoproducedielectricisolationfromtheacpowerline.Linearregulatorscanonlyproduceoutputvoltageslowerthantheirinputvoltagesandeachlinearregulatorcanproduceonlyoneoutputvoltage.Eachlinearregulatorhasanaverageefficiency

ofbetween35and50percent.Thelossesaredissipatedasheat.

PWMswitchingpowersupplies

PWMswitchingpowersuppliesaremuchmoreefficientandflexibleintheirusethanlinearregulators.Onecommonlyfindsthemusedwithinportableproducts,aircraftandautomotiveproducts,smallinstruments,off-lineapplications,andgenerallythoseapplicationswherehighefficiencyandmultipleoutputvoltagesarerequired.Theirweightismuchlessthanthatoflinearregulatorssincetheyrequirelessheatsinkingforthesameoutputratin