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0 v
−12 v
+12 v
电流
OUTP
OUTN
差别的
电压
横过
加载
0 v
−12 v
+12 v
电流
OUTP
OUTN
差别的
电压
横过
加载
输出 = 0 v
输出 > 0 v
效率:lcfilterrequiredwiththetraditionalclass-dmodulationscheme
TPA3008D2
SLOS435A–MAY2004–REVISEDJULY2004
applicationinformation(持续)
figure18.thetpa3008d2outputvoltageandcurrentwaveformsintoaninductiveload
themainreasonthatthetraditionalclass-damplifierneedsanoutputfilteristhattheswitchingwaveformresults
inmaximumcurrentflow.thiscausesmorelossintheload,whichcauseslowerefficiency.theripplecurrentis
largeforthetraditionalmodulationscheme,becausetheripplecurrentisproportionaltovoltagemultipliedbythe
timeatthatvoltage.thedifferentialvoltageswingis2xv
CC
,andthetimeateachvoltageishalftheperiodfor
thetraditionalmodulationscheme.anideallcfilterisneededtostoretheripplecurrentfromeachhalfcyclefor
thenexthalfcycle,whileanyresistancecausespowerdissipation.thespeakerisbothresistiveandreactive,
whereasanlcfilterisalmostpurelyreactive.
TheTPA3008D2modulationschemehaslittlelossintheloadwithoutafilterbecausethepulsesareshortand
thechangeinvoltageisV
CC
insteadof2xV
CC
.astheoutputpowerincreases,thepulseswiden,makingthe
ripplecurrentlarger.ripplecurrentcouldbefilteredwithanlcfilterforincreasedefficiency,butformost
applicationsthefilterisnotneeded.
anlcfilterwithacutofffrequencylessthantheclass-dswitchingfrequencyallowstheswitchingcurrenttoflow
throughthefilterinsteadoftheload.thefilterhaslessresistancethanthespeaker,whichresultsinlesspower
消耗,thereforeincreasingefficiency.
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