台湾聚鼎PTTC一级代理分销KOYUELEC光与电子TVS Selection Guide

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TransientVoltageSuppressionDiodesTVSDiodeSelectionChecklist1.DefineCircuitOperatingParametersNormaloperatingvoltagetypeinDCorAC:DeviceTypeRequired:Uni-drectionalBi-directionalNormaloperatingvoltageinvolts:Maximumtransientcurrent(Ipp):Maximumclampingvoltage(Vc):Requiredpeakreversesurgepowerrating:Productmountingtype(package):Operatingtemperature:2.NarrowTVSDiodeSeriesfortheApplicationPleaserefertotheproductselectionchartsanddatasheetswithinthisguide,factoringthesekeyparameters:ReverseStandoffVoltage(VR):ThedeviceVRshouldbeequalto,orgreatthan,thepeakoperatinglevelofthecircuit(orpartofthecircuit)tobeprotected.ThisistoensurethatTVSDiodedoesnotclipthecircuitdrivevoltage.PeakPulseCurrent(IPP):ThePeakPulseCurrent(IPP)identifiesthemaximumcurrenttheTVSDiodecanwithstandwithoutdamage.TherequiredIPPcanonlybedeterminedbydividingthepeaktransientvoltagebythesourceimpedance.NotethattheTVSDiodefailuremechanismisashortcircuit;iftheTVSDiodefailsduetoatransient,thecircuitwillstillbeprotected.MaximumClampingVoltage(VC):ThisthepeakvoltagethatwillappearacrosstheTVSDiodewhensubjectedtothePeakPulseCurrent(IPP),basedon10/1000μsexponentialwaveform.TheVCofeachTVSDiodeisidentifiedineachseriesdatasheetelectricalcharacteristicstable.MaximumratingsandchracteristicsRatingsat25ćambienttemperatureunlessotherwisespecified.3.VerifyAmbientOperatingParametersEnsurethattheapplicationvoltageislessthanorequaltothedevice’sstandoffvoltage,andthattheoperatingtemperaturelimitsarewithinthosespecifiedbythedevice.4.VerifyDeviceMountingStyleandDimensionsPleaserefertothedimensiondrawingscontainedwithinthedatasheetofeachseries.5.TesttheSelectedDeviceinActualApplicationPleasecontactPolytronicsifyouwouldlikeassistancewithtestingandverifyingsuitabilityofaPolytronicsdevicewithinyourproduct.Wehaveextensiveproducetestinglabcapabilitiesandtechnicalexpertisetoassistyou.新竹市科學工業園區工業東四路24-1號No.24-1IndustryE.Rd.IV,HsinchuSciencePark,Hsinchu300,Taiwan.TEL:+886-3-5643931FAX:+886-3-5644624http://www.pttc.com.tw

1TransientVoltageSuppressionDiodesTVSDiodeTerms&DefinitionsClampingDeviceTVSisaclampingdevicethatlimitsvoltagespikesbylowimpedanceavalanchebreakdownofaruggedsiliconPNjunction.Itisusedtoprotectsensitivecomponentsfromelectricaloverstressgeneratedbyinducedlightning,inductiveloadswitchingandelectrostaticdischarge.OperatingTemperatureRangeTheminimumandmaximumambientoperatingtemperatureofthecircuitinwhichadevicewillbeapplied.Operatingtemperaturedoesnotallowfortheeffectsofadjacentcomponents,thisisaparameterthedesignermusttakeintoconsideration.CapacitanceThepropertyofacircuitelementthatpermitsittostoreanelectricalcharge.Incircuitprotection,theoff-statecapacitanceistypicallymeasuredat1MHz.ReverseStandoffVoltage(VR)Inthecaseofauni-directionalTVSdiode,thisisthemaximumpeakvoltagethatmaybeappliedinthe‘blockingdirection’withnosignificantcurrentflow.Inthecaseofabi-directionaltransient,itappliesineitherdirection.ItisthesamedefinitionasMaximumOff-stateVoltageandMaximumWorkingVoltage.BreakdownVoltage(VBR)BreakdownvoltagemeasuredataspecifiedDCtestcurrent,typically1mA.Usuallyaminimumandmaximumisspecified.PeakPulseCurrent(IPP)Maximumpulsecurrentwhichcanbeappliedrepetitively.Usuallya10/1000μsdoubleexponentialwaveform,butcanalsobe8/20μs,ifstated.MaximumClampingVoltage(VCorVCI)MaximumvoltagewhichcanbemeasuredacrosstheprotectorwhensubjectedtotheMaximumPeakPulseCurrent.PeakPulsePower(PPP)ExpressedinWattsorKilowatts,fora1msexponentialtransfientfitfisIPPmultipliedbyVC.新竹市科學工業園區工業東四路24-1號No.24-1IndustryE.Rd.IV,HsinchuSciencePark,Hsinchu300,Taiwan.TEL:+886-3-5643931FAX:+886-3-5644624http://www.pttc.com.tw

2TransientVoltageSuppressionDiodesTVSDiodeTransientVoltageScenariosElectrostaticdischargeischaracterizedbyveryfastrisetimesandveryhighpeakvoltagesandcurrents.Thisenergyistheresultofanimbalanceofpositiveandnegativechargesbetweenobjects.ESDthatisgeneratedbyeverydayactivitiescanfarsurpassthevulnerabilitythresholdofstandardsemiconductortechnologies.Followingareafewexamples:Walkingacrossacarpet:35kV@RH=20%;1.5kV@RH=65%Walkingacrossavinylfloor:12kV@RH=20%;250V@RH=65%Workeratabench:6kV@RH=20%;100V@RH=65%Vinylenvelopes:7kV@RH=20%;600V@RH=65%Polybagpickedupfromdesk:20kV@RH=20%;1.2kV@RH=65%LightningInducedTransientsEventhoughadirectstrikeisclearlydestructive,transientsinducedbylightningarenottheresultofadirectstrike.Whenalightningstrikeoccurs,theeventcreatesamagneticfieldwhichcaninducetransientsoflargemagnitudeinnearbyelectricalcables.Acloud-to-cloudstrikewilleffectnotonlyoverheadcables,butalsoburiedcables.Evenastrike1miledistant(1.6km)cangenerate70voltsinelectricalcables.Inacloud-to-groundstrike(asshownatright)thetransientgeneratingeffectisfargreater.Thisdiagramshowsatypicalcurrentwaveformforinducedlightningdisturbances.InductiveLoadSwitchingTheswitchingofinductiveloadsgenerateshighenergytransientswhichincreaseinmagnitudewithincreasinglyheavyloads.Whentheinductiveloadisswitchedoff,thecollapsingmagneticfieldisconvertedintoelectricalenergywhichtakestheformofadoubleexponentialtransient.Dependingonthesource,thesetransientscanbeaslargeashundredsofvoltsandhundredsofAmps,withdurationtimesof400milliseconds.Typicalsourcesofinductivetransientsinclude:‧Generator‧Motor‧Relay‧TransformerTheseexamplesarecommoninelectricalandelectronicsystems.Becausethesizesoftheloadsvaryaccordingtotheapplication,thewaveshape,duration,peakcurrentandpeakvoltageareallvariableswhichexistinrealworldtransients.Oncethesevariablescanbeapproximated,asuitablesuppressortechnologycanbeselected.Thediagramatrightshowsatransientwhichistheresultofstoredenergywithinthealternatorofanautomobilechargingsystem.AsimilartransientcanalsobecausedbyotherDCmotorsinavehicle.Forexample,DCmotorspoweramenitiessuchaspowerlocks,seatsandwindows.ThesevariousapplicationsofaDCmotorcanproducetransientsthatarejustasharmfultothesensitiveelectroniccomponentsastransientscreatedintheexternalenvironment.新竹市科學工業園區工業東四路24-1號No.24-1IndustryE.Rd.IV,HsinchuSciencePark,Hsinchu300,Taiwan.TEL:+886-3-5643931FAX:+886-3-5644624http://www.pttc.com.tw

3TransientVoltageSuppressionDiodesTVSDiodeOvervoltageSuppressionFactsVoltageTransientsaredefinedasshortdurationsurgesofelectricalenergyandaretheresultofthesuddenreleaseofenergypreviouslystoredorinducedbyothermeans,suchasheavyinductiveloadsorlightning.Inelectricalorelectroniccircuits,thisenergycanbereleasedinapredictablemannerviacontrolledswitchingactions,orrandomlyinducedintoacircuitfromexternalsources.Repeatabletransientsarefrequentlycausedbytheoperationofmotors,generators,ortheswitchingofreactivecircuitcomponents.Randomtransients,ontheotherhand,areoftencausedbyLightningandElectrostaticDischarge(ESD).LightningandESDgenerallyoccurunpredictably,andmayrequireelaboratemonitoringtobeaccuratelymeasured,especiallyifinducedatthecircuitboardlevel.Numerouselectronicsstandardsgroupshaveanalyzedtransientvoltageoccurrencesusingacceptedmonitoringortestingmethods.Thekeycharacteristicsofseveraltransientsareshowninthetablebelow.CharacteristicsofTransientVoltageSpikesTransientvoltagespikesgenerallyexhibita“doubleexponential”wave,asshownbelowforlightningandESD.Theexponentialrisetimeoflightningisintherange1.2μsecto10μsec(essentially10%to90%)andthedurationisintherangeof50μsecto1000μsec(50%ofpeakvalues).ESDontheotherhand,isamuchshorterdurationevent.Therisetimehasbeencharacterizedatlessthan1.0ns.Theoveralldurationisapproximately100ns.WhyareTransientsofIncreasingConcern?Componentminiaturizationhasresultedinincreasedsensitivitytoelectricalstresses.Microprocessorsforexample,havestructuresandconductivepathswhichareunabletohandlehighcurrentsfromESDtransients.Suchcomponentsoperateatverylowvoltages,sovoltagedisturbancesmustbecontrolledtopreventdeviceinterruptionandlatentorcatastrophicfailures.Sensitivemicroprocessorsareprevelanttodayinawiderangeofdevices.Everythingfromhomeappliances,suchasdishwashers,toindustrialcontrolsandeventoysusemicroprocessorstoimprovefunctionalityandefficiency.Mostvehiclesnowalsoemploymultipleelectronicsystemstocontroltheengine,climate,brakingand,insomecases,steering,tractionandsafetysystems.Manyofthesub-orsupportingcomponents(suchaselectricmotorsoraccessories)withinappliancesandautomobilespresenttransientthreatstotheentiresystem.Carefulcircuitdesignshouldnotonlyfactorenvironmentalscenariosbutalsothepotentialeffectsoftheserelatedcomponents.Table2belowshowsthevulnerabilityofvariouscomponenttechnologies.新竹市科學工業園區工業東四路24-1號No.24-1IndustryE.Rd.IV,HsinchuSciencePark,Hsinchu300,Taiwan.TEL:+886-3-5643931FAX:+886-3-5644624http://www.pttc.com.tw