外文翻译--LED是如何工作的.doc -- 5 元

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.WhatisaDiodeAdiodeisthesimplestsortofsemiconductordevice.Broadlyspeaking,asemiconductorisamaterialwithavaryingabilitytoconductelectricalcurrent.Mostsemiconductorsaremadeofapoorconductorthathashadimpuritiesatomsofanothermaterialaddedtoit.Theprocessofaddingimpuritiesiscalleddoping.InthecaseofLEDs,theconductormaterialistypicallyaluminumgalliumarsenide.Inpurealuminumgalliumarsenide,alloftheatomsbondperfectlytotheirneighbors,leavingnofreeelectronsnegativelychargedparticlestoconductelectriccurrent.Indopedmaterial,additionalatomschangethebalance,eitheraddingfreeelectronsorcreatingholeswhereelectronscango.Eitheroftheseadditionsmakethematerialmoreconductive.AsemiconductorwithextraelectronsiscalledNtypematerial,sinceithasextranegativelychargedparticles.InNtypematerial,freeelectronsmovefromanegativelychargedareatoapositivelychargedarea.AsemiconductorwithextraholesiscalledPtypematerial,sinceiteffectivelyhasextrapositivelychargedparticles.Electronscanjumpfromholetohole,movingfromanegativelychargedareatoapositivelychargedarea.Asaresult,theholesthemselvesappeartomovefromapositivelychargedareatoanegativelychargedarea.AdiodecomprisesasectionofNtypematerialbondedtoasectionofPtypematerial,withelectrodesoneachend.Thisarrangementconductselectricityinonlyonedirection.Whennovoltageisappliedtothediode,electronsfromtheNtypematerialfillholesfromthePtypematerialalongthejunction2betweenthelayers,formingadepletionzone.Inadepletionzone,thesemiconductormaterialisreturnedtoitsoriginalinsulatingstatealloftheholesarefilled,sotherearenofreeelectronsoremptyspacesforelectrons,andchargecantflow.Togetridofthedepletionzone,youhavetogetelectronsmovingfromtheNtypeareatothePtypeareaandholesmovinginthereversedirection.Todothis,youconnecttheNtypesideofthediodetothenegativeendofacircuitandthePtypesidetothepositiveend.ThefreeelectronsintheNtypematerialarerepelledbythenegativeelectrodeanddrawntothepositiveelectrode.TheholesinthePtypematerialmovetheotherway.Whenthevoltagedifferencebetweentheelectrodesishighenough,theelectronsinthedepletionzoneareboostedoutoftheirholesandbeginmovingfreelyagain.Asaresult,thedepletionzonedisappears.WhenthenegativeendofthecircuitishookeduptotheNtypelayerandthepositiveendishookeduptoPtypelayer,electronsandholesstartmoving.IfthePtypesideisconnectedtothenegativeendofthecircuitandtheNtypesideisconnectedtothepositiveend,currentwillnotflow.Nocurrentflowsacrossthejunctionbecausetheholesandtheelectronsareeachmovinginthewrongdirection.WhenthepositiveendofthecircuitishookeduptotheNtypelayerandthenegativeendishookeduptothePtypelayer,thedepletionzonegetsbigger.TheinteractionbetweenelectronsandholeshasaninterestingeffectitgenerateslightInthenextsection,wellfindoutexactlywhythisis.HowCanaDiodeProduceLightLightisaformofenergythatcanbereleasedbyanatom.Itismadeupofmanysmallparticlelikepacketsthathaveenergy.Theseparticles,calledphotons,arethemostbasicunitsoflight.Photonsarereleasedasaresultofmovingelectrons.Inanatom,electronsmoveinorbitalsaroundthenucleus.Electronsindifferentorbitalshavedifferentamountsofenergy.Generallyspeaking,electronswithgreaterenergymoveinorbitalsfartherawayfromthenucleus.Foranelectrontojumpfromalowerorbitaltoahigherorbital,somethinghastoboostitsenergylevel.Conversely,anelectronreleasesenergywhenitdropsfromahigherorbitaltoalowerone.Thisenergyisreleasedintheformofaphoton.Agreaterenergydropreleasesahigherenergyphoton,whichischaracterizedbyahigherfrequency.Aswesawinthelastsection,freeelectronsmovingacrossadiodecanfallintoemptyholesfromthePtypelayer.Thisinvolvesadropfromtheconductionbandtoalowerorbital,sotheelectronsreleaseenergyintheformofphotons.Thishappensinanydiode,butyoucanonlyseethephotonswhenthediodeiscomposedofcertainmaterial.Theatomsinastandardsilicondiode,forexample,are3arrangedinsuchawaythattheelectrondropsarelativelyshortdistance.Asaresult,thephotonsfrequencyissolowthatitisinvisibletothehumaneyeitisintheinfraredportionofthelightspectrum.Thisisntnecessarilyabadthing,ofcourseInfraredLEDsareidealforremotecontrols,amongotherthings.VisiblelightemittingdiodesVLEDs,suchastheonesthatlightupnumbersinadigitalclock,aremadeofmaterialscharacterizedbyawidergapbetweentheconductionbandandthelowerorbitals.Thesizeofthegapdeterminesthefrequencyofthephotoninotherwords,itdeterminesthecolorofthelight.Whilealldiodesreleaselight,mostdontdoitveryeffectively.Inanordinarydiode,thesemiconductormaterialitselfendsupalotofthelightenergy.LEDsarespeciallyconstructedtoreleasealargenumberofphotonsoutward.Additionally,theyarehousedinaplasticbulbthatconcentratesthelightinaparticulardirection.LEDshaveseveraladvantagesoverconventionalincandescentlamps.Foronething,theydonthaveafilamentthatwillburnout,sotheylastmuchlonger.Additionally,theirsmallplasticbulbmakesthemalotmoredurable.Theyalsofitmoreeasilyintomodernelectroniccircuits.Butthemainadvantageisefficiency.Inconventionalincandescentbulbs,thelightproductionprocessinvolvesgeneratingalotofheat.Thisiscompletelywastedenergy,unlessyoureusingthelampasaheater.LEDsgenerateverylittleheat,relativelyspeaking.Amuchhigherpercentageoftheelectricalpowerisgoingdirectlytogeneratinglight,whichcutsdownontheelectricitydemandsconsiderably.Upuntilrecently,LEDsweretooexpensivetouseformostlightingapplications.Thepriceofsemiconductordeviceshasplummetedoverthepastdecade,however,makingLEDsamorecosteffectivelightingoptionforawiderangeofsituations.Whiletheymaybemoreexpensivethanincandescentlightsupfront,theirlowercostinthelongruncanmakethemabetterbuy.Inthefuture,theywillplayanevenbiggerroleintheworldoftechnology.TRANSIENTVOLTAGESUPPRESSORTVSDiodePRESENTATIONHighprotectiononsensitivemobileelectronicdevicesFollowstrictlytotheIEC6100042ESDteststandardUsingthebehaviorofdiodeP/NjunctiontoachieveESDprotectionWhatareTransientVoltagesThesearefaultswhichcausethevoltagetogooutsidenormallimitsforaperiodoftime.TransientvoltagesarecharacterizedbythreethingsVeryHighVoltage,OccurForAVeryShortPeriodoftimeinnanosecondsandHighOccurrence.Manytransientscausedamagetomicrosemiconductorchipsetsbydegradingtheirperformance.Thisdamageiscumulativeandeventuallyreachesapointwheresuddenandcompletefailureof4thecomponentresults.Moreover,sometransientsarecapableofcausingimmediateequipmentfailures.Equipmentfailurescausedbytransientsarehardtodetectandareoftenincorrectlyblamedonotherperceivedcauses.Microsemiconductorchipsetsdamagedbytransientsoftenrequiresophisticatedinstrumenttoreplacethemwhichmakethemexpensivetorepair.Theonlycureistoclamptransientstoasafelevelwheretheprotectedloadcanwithstand.TVSdiodesAdvantagesTVSDiodevs.ZenerDiodeComparedwiththetraditionalZenerdiode,TVSdiodehasalargerP/Ncrosssection.TVSdiodecomponentisconstructedanddesignedtoabsorblargeramountsofenergy,joules,withafasterresponsetimethanZenerdiode.Zenerdiodehasahigherclampingvoltageandheatdissipationisslower.TVSDiodevs.MultilayerMetaloxideVaristor,MLVAmajordifferencebetweenTVSdiodeandMLVis,asMLVabsorbstransientenergy,itselectricalparameterssuchasLeakagecurrentandBreakdownvoltagetendtodriftawayfromtheiroriginalspecificationswhichexhibitsaninherentwearoutmechanismwithinthestructure.Becauseofitshighimpedance,itsclampingratiocanreachashighas3.ThereforeMLVismoresuitabletobeappliedonlesssensitivelineswhereitshighclampingvoltagecanbetolerated.TVSDiodevs.CeramicCapacitorCeramiccapacitorisnotabletowithstandahightransientvoltage.A10kVtransientvoltagewilldestroyabout60ofthecomponentoftheceramiccapacitorwhileTVSdiodeisabletowithstandupto15Kvtransientvoltage.CeramiccapacitorisalsonotabletodissipateheatefficientlylikewhatTVSdiodedoeswhentransientoccurs.TVSDiodevs.GasDischargeTubes,GDTsTVSdiodelimitsvoltagespiketoacceptablelevelbyclampingwhileGDTlimitsvoltagespikebycrowbaraction.GDTconductswhenitsthresholdvoltageisexceededandthentriggertoanonstatevoltageofonlyafewvolts.AdrawbackofGDTprotectionisthatthetriggeronstatevoltageisbelowtheoperatingvoltageoftheprotectedload.Theprotectedloadwillbeshutdowntemporarily.