分立LED的MTBF计算方法

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MTBFFORDISCRETELEDSANDPHOTODIODES
ThecalculationofMeanTimeBetweenFailure(MTBF)isoftenrequiredasanaidinpredictingthereliabilityofelectronicequipmentunderdifferentoperatingconditions.ThevalueofMTBFforacomponentisbaseduponfailure-ratemodelswhichhavebeendevelopedinconjunctionwithMIL-HDBK-217E.TheMTBFisnotaguaranteeofuseableproductlifetime,butisaguideforplanningtheoperationaluseoftheequipment.Theaccuracyofthevaluescalculatedisdependentuponthevalidityofthemodels.Also,thevalueschosenfortheoperatingparametersmustberepresentativeoftheoperatingparametersduringactualuse.Inthecaseoffiberopticdatacommunicationequipment,anareaofprimaryconcernistheMTBFvaluesforthediscreteLightEmittingDiodes(LEDs)andphotodiodesusedinthefiberoptictransmittersandreceivers.

ThedeterminationofthepredictedMTBFforanLEDorphotodiodeisacalculationusingthepartfailure-ratemodelforoptoelectronicdevicesasfoundinsection5.1.3.10ofMIL-HDBK-217E.Thepartfailure-ratemodel,lP,isasfollows:where:ThevalueforMTBFisthendeterminedfrom:Threeoftheabovementionedfactorsareexplicitlydefinedinsection5.1.3.10ofMIL-HDBK-217E(lB,IIE,andIIQ).Valuesforthesefactors,alongwithdescriptionsofthevariousconditionsidentifiedbyMIL-HDBK-217Earediscussedinthisnote.Thefourthparameter,IIT,maybeobtainedeitherfromtablesprovidedinMIL-HDBK-217Eorfromcalculationsinvolvingparametricdataobtainedfromthedeviceduringactualorsimulatedoperation.IdentificationoftheseparametersandspecificdataapplicabletocomponentsmanufacturedbyHoneywellarealsocontainedinthisapplicationnote.

ThereareseveralsamplecalculationstoaidtheuserindeterminingMTBFvaluesfortheparticularcomponentswhichheisconsidering.Inaddition,thereareanumberoftablesincludedinwhichMTBFvaluesarelistedforvarioustypesofdevicesunderdifferentoperatingconditions.BASEFAILURERATEThedevicebasefailure-rate,lB,isgiveninTable5.1.3.10-3ofMIL-HDBK-217E.ThevaluesforLEDandphotodiodesareshownbelow.BaseFailure-Rate(fromMIL-HDBK-217E,Table5.1.3.10-3)QUALITYFACTORThequalityfactorisgiveninTable5.1.3.10-4ofMIL-HDBK-217E.Thisisreproducedbelowalongwithabriefdescriptionofthevariousqualitylevels.QualityFactors(fromMIL-HDBK-217E,Table5.1.3.10-4)QualityLevelIIQDescriptionJANTXV0.001FulltestingasdefinedbyMIL-S-19500includingScreeningandGroupsA,B,andC.JANTX0.02IdenticaltoJANTXVexceptdoesnotincludethe100%precapvisualinspectioncontainedinScreening.JAN0.1TestingasdefinedbyMIL-S-19500includingGroupsA,B,andC,butnotincludingScreening.LOWER0.5AppliestoallhermeticpackagedLEDsandphotodiodes.PLASTIC1.0Appliestoalldevicesencapsulatedwithorganicmaterials.Productsmeetinganyofthequalitylevelsdefinedinthequalityfactorstable(MIL-HDBK-217E,Table5.1.3.10-4)areavailablefromHoneywell.WhilethereareveryfewfiberoptictypeproductsdefinedbyaslashsheettoMIL-S-19500,atestprogramcanbedesignedwhichwillcarryouttheintentionofMIL-S-19500foranyofthe”metalwindowcan”deviceswhichHoneywelloffers.ApplicationNoteCalculatingMeanTimeBetweenFailureforDiscreteLEDsandPhotodiodesP=BTEQfailures106hoursT=temperaturefactorE=environmentalfactorQ=qualityfactorB=basefailure-ratefailures106hoursMTBF=1PforasingleLED0.0011failures106hoursforaphotodiodeand0.00065failures106hoursB=B=©HoneywellEuropeS.A.Honeywellreservestherighttomakechangesinordertoimprovedesignandsupplythebestproductspossible.
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[[i]本帖最后由paulyu于2007-9-2711:19编辑[/i]]