www.德州仪器.com
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单独的-endedoperation
BTLAMPLIFIEREFFICIENCY
TPA6011A4
SLOS392A–FEBRUARY2002–REVISEDJULY2004
inatypicalcomputersoundchanneloperatingat5v,bridgingraisesthepowerintoan8-
Ω
speakerfroma
singled-结束(se,groundreference)limitof250mwto1w.insoundpowerthatisa6-dbimprovement,这个
isloudnessthatcanbeheard.inadditiontoincreasedpowertherearefrequencyresponseconcerns.考虑
thesingle-supplyseconfigurationshowninfigure37.acouplingcapacitorisrequiredtoblockthedcoffset
voltagefromreachingtheload.thesecapacitorscanbequitelarge(approximately33µfto1000µf),sothey
tendtobeexpensive,重的,occupyvaluablepcbarea,andhavetheadditionaldrawbackoflimiting
低-frequencyperformanceofthesystem.thisfrequencylimitingeffectisduetothehigh-passfilternetwork
createdwiththespeakerimpedanceandthecouplingcapacitanceandiscalculatedwithequation6.
forexample,a68-µfcapacitorwithan8-
Ω
speakerwouldattenuatelowfrequenciesbelow293hz.thebtl
configurationcancelsthedcoffsets,whicheliminatestheneedfortheblockingcapacitors.低-频率
performanceisthenlimitedonlybytheinputnetworkandspeakerresponse.costandpcbspacearealso
minimizedbyeliminatingthebulkycouplingcapacitor.
figure37.单独的-endedconfigurationandfrequencyresponse
increasingpowertotheloaddoescarryapenaltyofincreasedinternalpowerdissipation.theincreased
dissipationisunderstandableconsideringthattheBTLconfigurationproduces4
×
theoutputpoweroftheSE
配置.internaldissipationversusoutputpowerisdiscussedfurtherinthe
crestfactorandthermal
仔细考虑
部分.
insemode(seefigure37),theloadisdrivenfromtheprimaryamplifieroutputforeachchannel(out+).
theamplifierswitchessingle-endedoperationwhenthese/btlterminalisheldhigh.thisputsthenegative
outputsinahigh-impedancestate,andeffectivelyreducestheamplifier'sgainby6db.
类-abamplifiersareinefficient.theprimarycauseoftheseinefficienciesisvoltagedropacrosstheoutput
stagetransistors.therearetwocomponentsoftheinternalvoltagedrop.oneistheheadroomordcvoltage
dropthatvariesinverselytooutputpower.thesecondcomponentisduetothesinewavenatureoftheoutput.
ThetotalvoltagedropcanbecalculatedbysubtractingtheRMSvalueoftheoutputvoltagefromV
DD
.这
internalvoltagedropmultipliedbythermsvalueofthesupplycurrent(i
DD
rms)determinestheinternalpower
dissipationoftheamplifier.
aneasy-至-useequationtocalculateefficiencystartsoutasbeingequaltotheratioofpowerfromthepower
supplytothepowerdeliveredtotheload.toaccuratelycalculatethermsandaveragevaluesofpowerinthe
loadandintheamplifier,thecurrentandvoltagewaveformshapesmustfirstbeunderstood(seefigure38).
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