外文翻译--LED是如何工作的.doc

1英文原文HowLightEmittingDiodesWorkLightemittingdiodes,commonlycalledLEDs,arerealunsungheroesintheelectronicsworld.Theydodozensofdifferentjobsandarefoundinallkindsofdevices.Amongotherthings,theyformthenumbersondigitalclocks,transmitinformationfromremotecontrols,lightupwatchesandtellyouwhenyourappliancesareturnedon.Collectedtogether,theycanformimagesonajumbotelevisionscreenorilluminateatrafficlight.Basically,LEDsarejusttinylightbulbsthatfiteasilyintoanelectricalcircuit.Butunlikeordinaryincandescentbulbs,theydonthaveafilamentthatwillburnout,andtheydontgetespeciallyhot.Theyareilluminatedsolelybythemovementofelectronsinasemiconductormaterial,andtheylastjustaslongasastandardtransistor.Inthisarticle,wellexaminethesimpleprinciplesbehindtheseubiquitousblinkers,illuminatingsomecoolprinciplesofelectricityandlightintheprocess.WhatisaDiode?Adiodeisthesimplestsortofsemiconductordevice.Broadlyspeaking,asemiconductorisamaterialwithavaryingabilitytoconductelectricalcurrent.Mostsemiconductorsaremadeofapoorconductorthathashadimpurities(atomsofanothermaterial)addedtoit.Theprocessofaddingimpuritiesiscalleddoping.InthecaseofLEDs,theconductormaterialistypicallyaluminum-gallium-arsenide.Inpurealuminum-gallium-arsenide,alloftheatomsbondperfectlytotheirneighbors,leavingnofreeelectrons(negatively-chargedparticles)toconductelectriccurrent.Indopedmaterial,additionalatomschangethebalance,eitheraddingfreeelectronsorcreatingholeswhereelectronscango.Eitheroftheseadditionsmakethematerialmoreconductive.AsemiconductorwithextraelectronsiscalledN-typematerial,sinceithasextranegatively-chargedparticles.InN-typematerial,freeelectronsmovefromanegatively-chargedareatoapositivelychargedarea.AsemiconductorwithextraholesiscalledP-typematerial,sinceiteffectivelyhasextrapositively-chargedparticles.Electronscanjumpfromholetohole,movingfromanegatively-chargedareatoapositively-chargedarea.Asaresult,theholesthemselvesappeartomovefromapositively-chargedareatoanegatively-chargedarea.AdiodecomprisesasectionofN-typematerialbondedtoasectionofP-typematerial,withelectrodesoneachend.Thisarrangementconductselectricityinonlyonedirection.Whennovoltageisappliedtothediode,electronsfromtheN-typematerialfillholesfromtheP-typematerialalongthejunction2betweenthelayers,formingadepletionzone.Inadepletionzone,thesemiconductormaterialisreturnedtoitsoriginalinsulatingstate-alloftheholesarefilled,sotherearenofreeelectronsoremptyspacesforelectrons,andchargecantflow.Togetridofthedepletionzone,youhavetogetelectronsmovingfromtheN-typeareatotheP-typeareaandholesmovinginthereversedirection.Todothis,youconnecttheN-typesideofthediodetothenegativeendofacircuitandtheP-typesidetothepositiveend.ThefreeelectronsintheN-typematerialarerepelledbythenegativeelectrodeanddrawntothepositiveelectrode.TheholesintheP-typematerialmovetheotherway.Whenthevoltagedifferencebetweentheelectrodesishighenough,theelectronsinthedepletionzoneareboostedoutoftheirholesandbeginmovingfreelyagain.Asaresult,thedepletionzonedisappears.WhenthenegativeendofthecircuitishookeduptotheN-typelayerandthepositiveendishookeduptoP-typelayer,electronsandholesstartmoving.IftheP-typesideisconnectedtothenegativeendofthecircuitandtheN-typesideisconnectedtothepositiveend,currentwillnotflow.Nocurrentflowsacrossthejunctionbecausetheholesandtheelectronsareeachmovinginthewrongdirection.WhenthepositiveendofthecircuitishookeduptotheN-typelayerandthenegativeendishookeduptotheP-typelayer,thedepletionzonegetsbigger.Theinteractionbetweenelectronsandholeshasaninterestingeffect-itgenerateslight!Inthenextsection,wellfindoutexactlywhythisis.HowCanaDiodeProduceLight?Lightisaformofenergythatcanbereleasedbyanatom.Itismadeupofmanysmallparticle-likepacketsthathaveenergy.Theseparticles,calledphotons,arethemostbasicunitsoflight.Photonsarereleasedasaresultofmovingelectrons.Inanatom,electronsmoveinorbitalsaroundthenucleus.Electronsindifferentorbitalshavedifferentamountsofenergy.Generallyspeaking,electronswithgreaterenergymoveinorbitalsfartherawayfromthenucleus.Foranelectrontojumpfromalowerorbitaltoahigherorbital,somethinghastoboostitsenergylevel.Conversely,anelectronreleasesenergywhenitdropsfromahigherorbitaltoalowerone.Thisenergyisreleasedintheformofaphoton.Agreaterenergydropreleasesahigher-energyphoton,whichischaracterizedbyahigherfrequency.Aswesawinthelastsection,freeelectronsmovingacrossadiodecanfallintoemptyholesfromtheP-typelayer.Thisinvolvesadropfromtheconductionbandtoalowerorbital,sotheelectronsreleaseenergyintheformofphotons.Thishappensinanydiode,butyoucanonlyseethephotonswhenthediodeiscomposedofcertainmaterial.Theatomsinastandardsilicondiode,forexample,are3arrangedinsuchawaythattheelectrondropsarelativelyshortdistance.Asaresult,thephotonsfrequencyissolowthatitisinvisibletothehumaneye-itisintheinfraredportionofthelightspectrum.Thisisntnecessarilyabadthing,ofcourse:InfraredLEDsareidealforremotecontrols,amongotherthings.Visiblelight-emittingdiodes(VLEDs),suchastheonesthatlightupnumbersinadigitalclock,aremadeofmaterialscharacterizedbyawidergapbetweentheconductionbandandthelowerorbitals.Thesizeofthegapdeterminesthefrequencyofthephoton-inotherwords,itdeterminesthecolorofthelight.Whilealldiodesreleaselight,mostdontdoitveryeffectively.Inanordinarydiode,thesemiconductormaterialitselfendsupalotofthelightenergy.LEDsarespeciallyconstructedtoreleasealargenumberofphotonsoutward.Additionally,theyarehousedinaplasticbulbthatconcentratesthelightinaparticulardirection.LEDshaveseveraladvantagesoverconventionalincandescentlamps.Foronething,theydonthaveafilamentthatwillburnout,sotheylastmuchlonger.Additionally,theirsmallplasticbulbmakesthemalotmoredurable.Theyalsofitmoreeasilyintomodernelectroniccircuits.Butthemainadvantageisefficiency.Inconventionalincandescentbulbs,thelight-productionprocessinvolvesgeneratingalotofheat.Thisiscompletelywastedenergy,unlessyoureusingthelampasaheater.LEDsgenerateverylittleheat,relativelyspeaking.Amuchhigherpercentageoftheelectricalpowerisgoingdirectlytogeneratinglight,whichcutsdownontheelectricitydemandsconsiderably.Upuntilrecently,LEDsweretooexpensivetouseformostlightingapplications.Thepriceofsemiconductordeviceshasplummetedoverthepastdecade,however,makingLEDsamorecost-effectivelightingoptionforawiderangeofsituations.Whiletheymaybemoreexpensivethanincandescentlightsupfront,theirlowercostinthelongruncanmakethemabetterbuy.Inthefuture,theywillplayanevenbiggerroleintheworldoftechnology.TRANSIENTVOLTAGESUPPRESSOR(TVS)DiodePRESENTATIONHighprotectiononsensitivemobileelectronicdevicesFollowstrictlytotheIEC61000-4-2ESDteststandardUsingthebehaviorofdiodeP/NjunctiontoachieveESDprotectionWhatareTransientVoltages?Thesearefaultswhichcausethevoltagetogooutsidenormallimitsforaperiodoftime.Transientvoltagesarecharacterizedbythreethings:VeryHighVoltage,OccurForAVeryShortPeriodoftime(innanoseconds)andHighOccurrence.Manytransientscausedamagetomicro-semiconductorchipsetsbydegradingtheirperformance.Thisdamageiscumulativeandeventuallyreachesapointwheresuddenandcompletefailureof4thecomponentresults.Moreover,sometransientsarecapableofcausingimmediateequipmentfailures.Equipmentfailurescausedbytransientsarehardtodetectandareoftenincorrectlyblamedonotherperceivedcauses.Microsemiconductorchipsetsdamagedbytransientsoftenrequiresophisticatedinstrumenttoreplacethemwhichmakethemexpensivetorepair.Theonlycureistoclamptransientstoasafelevelwheretheprotectedloadcanwithstand.TVSdiodesAdvantagesTVSDiodevs.ZenerDiodeComparedwiththetraditionalZenerdiode,TVSdiodehasalargerP/Ncrosssection.TVSdiodecomponentisconstructedanddesignedtoabsorblargeramountsofenergy,joules,withafasterresponsetimethanZenerdiode.Zenerdiodehasahigherclampingvoltageandheatdissipationisslower.TVSDiodevs.MultilayerMetaloxideVaristor,MLVAmajordifferencebetweenTVSdiodeandMLVis,asMLVabsorbstransientenergy,itselectricalparameterssuchasLeakagecurrentandBreakdownvoltagetendtodriftawayfromtheiroriginalspecificationswhichexhibitsaninherentwearoutmechanismwithinthestructure.Becauseofitshighimpedance,itsclampingratiocanreachashighas3.ThereforeMLVismoresuitabletobeappliedonlesssensitivelineswhereitshighclampingvoltagecanbetolerated.TVSDiodevs.CeramicCapacitorCeramiccapacitorisnotabletowithstandahightransientvoltage.A10kVtransientvoltagewilldestroyabout60%ofthecomponentoftheceramiccapacitorwhileTVSdiodeisabletowithstandupto15Kvtransientvoltage.CeramiccapacitorisalsonotabletodissipateheatefficientlylikewhatTVSdiodedoeswhentransientoccurs.TVSDiodevs.GasDischargeTubes,GDTsTVSdiodelimitsvoltagespiketoacceptablelevelbyclampingwhileGDTlimitsvoltagespikebycrowbaraction.GDTconductswhenitsthresholdvoltageisexceededandthentriggertoanon-statevoltageofonlyafewvolts.AdrawbackofGDTprotectionisthatthetriggeronstatevoltageisbelowtheoperatingvoltageoftheprotectedload.Theprotectedloadwillbeshutdowntemporarily.