www.德州仪器.com
EffectsofApplyingaSquareWaveIntoaSpeaker
效率 (theoretical, %)
R
L
R
L
r
ds(在)
100%
8
(8
1.3)
100%
86%
(1)
P
(总的)
P
O
效率
8.5 W
0.86
9.88 W
(2)
其它 losses
P
(总的)
(量过的)
P
(总的)
(theoretical)
10.49
9.88
0.61 W
(3)
P
(dis)
0.61 W
(12 V
22 毫安)
0.35 W
(4)
WhentoUseanOutputFilterforEMISuppression
TPA3008D2
SLOS435A–MAY2004–REVISEDJULY2004
applicationinformation(持续)
audiospecialistshaveadvisedforyearsnottoapplyasquarewavetospeakers.iftheamplitudeofthe
waveformishighenoughandthefrequencyofthesquarewaveiswithinthebandwidthofthespeaker,这
squarewavecouldcausethevoicecoiltojumpoutoftheairgapand/orscarthevoicecoil.a250-khzswitching
频率,不管怎样,doesnotsignificantlymovethevoicecoil,astheconemovementisproportionalto1/f
2
为
frequenciesbeyondtheaudioband.
damagemayoccurifthevoicecoilcannothandletheadditionalheatgeneratedfromthehigh-频率
switchingcurrent.theamountofpowerdissipatedinthespeakermaybeestimatedbyfirstconsideringthe
overallefficiencyofthesystem.iftheon-阻抗(rds(在))oftheoutputtransistorsisconsideredtocausethe
dominantlossinthesystem,thenthemaximumtheoreticalefficiencyforthetpa3008d2withan8-
Ω
loadisas
跟随:
themaximummeasuredoutputpowerisapproximately8.5wwithan12-vpowersupply.thetotaltheoretical
powersupplied(p(总的))forthisworst-caseconditionwouldthereforebeasfollows:
theefficiencymeasuredinthelabusingan8-
Ω
speakerwas81%.thepowernotaccountedforasdissipated
acrossther
ds(在)
maybecalculatedbysimplysubtractingthetheoreticalpowerfromthemeasuredpower:
thequiescentsupplycurrentat12vismeasuredtobe22ma.itcanbeassumedthatthequiescentcurrent
encapsulatesallremaininglossesinthedevice,i.e.,biasingandswitchinglosses.itmaybeassumedthatany
remainingpowerisdissipatedinthespeakerandiscalculatedasfollows:
notethatthesecalculationsarefortheworst-caseconditionof8.5wdeliveredtothespeaker.becausethe0.35
wisonly4%ofthepowerdeliveredtothespeaker,itmaybeconcludedthattheamountofpoweractually
dissipatedinthespeakerisrelativelyinsignificant.此外,thispowerdissipatediswellwithinthe
specificationsofmostloudspeakerdriversinasystem,asthepowerratingistypicallyselectedtohandlethe
powergeneratedfromaclippingwaveform.
designthetpa3008d2withoutthefilterifthetracesfromamplifiertospeakerareshort(<50cm).powered
扬声器,wherethespeakerisinthesameenclosureastheamplifier,isatypicalapplicationforclass-dwithout
afilter.
mostapplicationsrequireaferritebeadfilter.theferritefilterreducesemiaround1mhzandhigher(fccand
ceonlytestradiatedemissionsgreaterthan30mhz).whenselectingaferritebead,chooseonewithhigh
impedanceathighfrequencies,butlowimpedanceatlowfrequencies.
usealcoutputfilteriftherearelowfrequency(<1mhz)emi-sensitivecircuitsand/ortherearelongwiresfrom
theamplifiertothespeaker.
whenbothanlcfilterandaferritebeadfilterareused,thelcfiltershouldbeplacedascloseaspossibleto
theicfollowedbytheferritebeadfilter.
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