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南华大学船山学院毕业(设计)第1页，共18页DCswitchingpowersupplyforprotectiontechnologyAbstract:TheDCswitchingpowersupplyprotectionsystem,protectionsystemdesignprinciplesputforwardandthewholeprotectivemeasures,analysisoftheswitchingpowersupplyofthevariousprotectionfeaturesanddesign,introducesseveralpracticalprotectionCircuit.Keywords:switchingpowersupply;protectioncircuit;SystemDesign1IntroductionDCswitchingregulatorforuseinthemoreexpensivehigh-powerswitchingdevices,thecontrolcircuitisalsomorecomplex,Inaddition,theloadswitchingregulatorsaregenerallylevelwithalargenumberofhighlyintegratedelectronicsystemsinstalledonthedevice.Powertransistorsandintegrateddevicetolerance,poorthermalshocks.Thustheprotectionswitchingregulatorshouldtakeintoaccounttheregulatoritselfandloadsecurity.Manydifferenttypesofcircuitprotection,polarityprotectiondescribedhere,programprotection,overcurrentprotection,overvoltage,undervoltageprotectionandthermalprotectioncircuits.Someprotectionisusuallychosentobecombinedtoformacomprehensiveprotectionsystem.2polarityprotectionDCswitchingregulatorsaregenerallyunregulatedinputDCpowersupply.Duetooperationerrorsorunexpectedcircumstanceswillthewrongpolaritywilldamagetheswitchingpowersupply.Polarityprotectionpurposes,istomaketheswitchingregulatoronlywhenthecorrectpolarityconnectedtotheunregulatedDCpowertowork.Usingasingledevicecanbeachievedthroughthewizardpowerpolarityprotection.SimplepolarityprotectioncircuitshowninFigure1.ToflowthroughthediodeDswitchingregulator'sinputtotalcurrent,sothiscircuitisusedinlowpower南华大学船山学院毕业(设计)第2页，共18页switchingregulatoronthemoreappropriate.Inthehighpoweroftheoccasion,putthepolarityprotectioncircuitasapartoftheprotectionprogram,cansavethepowerrequiredforpolarityprotectiondiode,powerconsumptionwillbereduced.Forconvenientoperation,easytoidentifythepolarityiscorrectornot,thediodeinFigure1,thereceivedlight.3programprotectionSwitchingpowersupplycircuitismorecomplex,basicallycanbedividedintolow-powercontrolsectionandpowerswitchpart.Switchingtransistorsarehighpower,toprotecttheswitchingtransistoristurnedonoroffthepowerwhenthesecuritymustletmodulators,amplifiersandothersmallpowercontrolcircuit.Tothisend,toensurethatthecorrectbootprocess.Theinputofswitchingregulatortypicallytakeasmallinductanceandlargecapacitanceoftheinputfilter.Momentintheboot,willflowthroughalargefiltercapacitorinrushcurrent,theinrushcurrentcanbeseveraltimesthenormalinputcurrent.Makesuchalargesurgecurrentordinarypowerswitchcontactsorrelaycontactmelting,andtoenterthefuseblows.Inaddition,theinrushcurrentcanalsodamagethecapacitor,sothatshortenedlifeexpectancy,prematuredamage.Tothisend,thebootshouldbeaccesstoalimitingresistor,throughthecurrentlimitingresistortochargethecapacitor.Inordernottoconsumetoomuchofthecurrentlimitingresistorpower,whichaffectsthenormaloperationofswitchingregulators,power-transientprocessintheend,witharelayautomaticallypickitshortsoDCpowerdirectlytotheswitchingregulatorPowersupply,showninFigure2.Suchthattheswitchingregulatorcircuittermedasoftstartcircuit.南华大学船山学院毕业(设计)第3页，共18页Switchingregulatorcontrolcircuitlogiccomponentsorop-ampauxiliarypowersupplyrequired.Tothisend,theauxiliarypowersupplymustbeintheswitchcircuit.Thiscontrolcircuitcanbeusedtoensurethatthebootprocess.Normalbootprocessare:identificationofthepolarityoftheinputpower,voltageprotection→boot→auxiliarypowersupplycircuitandthroughthecurrentlimitingresistorRoftheswitchingregulatorinputcapacitorCcharging→modulationswitchingregulatorcircuit,→shortcircuitlimitingresistorswitchingregulatorstability.Intheswitchingregulator,thejust-machine,becausetheoutputcapacitorcapacity,ratedoutputvoltagechargetotakesometime.Duringthistime,thesamplingamplifierinputlowoutputvoltagesampling,closed-loopregulationcharacteristicsofthesystemwillforcetheswitchingtransistorconductiontimelonger,thisway,theswitchingtransistorduringthisperiodwilltendtocontinuousconductionAndeasilydamaged.Todothis,startthisperiodoftimerequired,theswitchingmodulationcircuitoutputtotheswitchingtransistorbasedrivesignalpulse-widthmodulation,toensuretheswitchtransistorgraduallybecomenormalbytheendoftheswitchstate,andthereforeshouldbeprotectedtomeettheadditionalpowerofsoftStart.4over-currentprotectionWhentheloadshort-circuit,overload,orunforeseencircumstancessuchasthefailurecontrolcircuits,willcauseflowthroughtheregulatorintheswitchingtransistorcurrentistoolarge,thepipeincreasespowerconsumption,heat,ifthereisnoover-currentprotectiondevices,powerswitchingtransistorTheremaybedamaged.Thereforetheswitchingregulatorintheover-currentprotectioniscommonlyused.Themosteconomicandsimplemethodistofuse.Heatcapacityofthetransistorissmall,generallycannotplaynormalfuseprotection,commonlyusedisfastfuse.This南华大学船山学院毕业(设计)第4页，共18页approachhastheadvantageofprotectioniseasy,however,needtoswitchtransistoraccordingtothespecificrequirementsofthesafetyoftheworkareatoselectthefusespecifications.Thisdisadvantageisover-currentprotectionmeasurestobringtheinconvenienceoffrequentlyreplacingthefuse.Commonlyusedlinearregulatorcurrentlimit