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类-doperation
traditionalclass-dmodulationscheme
0 v
−12 v
+12 v
电流
OUTP
差别的 voltage
横过 加载
OUTN
TPA3008D2ModulationScheme
TPA3008D2
SLOS435A–MAY2004–REVISEDJULY2004
applicationinformation(持续)
thissectionfocusesontheclass-doperationofthetpa3008d2.
thetraditionalclass-dmodulationscheme,whichisusedinthetpa032d0xfamily,hasadifferentialoutput
whereeachoutputis180degreesoutofphaseandchangesfromgroundtothesupplyvoltage,v
CC
.因此,
thedifferentialprefilteredoutputvariesbetweenpositiveandnegativeV
CC
,wherefiltered50%dutycycleyields
0vacrosstheload.thetraditionalclass-dmodulationschemewithvoltageandcurrentwaveformsisshownin
figure17.notethatevenatanaverageof0vacrosstheload(50%dutycycle),thecurrenttotheloadishigh,
causinghighlossandthuscausingahighsupplycurrent.
figure17.traditionalclass-dmodulationscheme'soutputvoltageandcurrentwaveformsintoan
InductiveLoadWithNoInput
thetpa3008d2usesamodulationschemethatstillhaseachoutputswitchingfrom0tothesupplyvoltage.
不管怎样,outpandoutnarenowinphasewitheachotherwithnoinput.thedutycycleofoutpisgreater
than50%andoutnislessthan50%forpositiveoutputvoltages.thedutycycleofoutpislessthan50%and
outnisgreaterthan50%fornegativeoutputvoltages.thevoltageacrosstheloadsitsat0vthroughoutmost
oftheswitchingperiod,greatlyreducingtheswitchingcurrent,whichreducesanyi
2
rlossesintheload.
13