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V
(lrms)
V
O
I
DD
I
dd(avg)
效率 的 一个 BTL 放大器
P
L
P
SUP
在哪里:
P
L
V
L
rms
2
R
L
, 和 V
LRMS
V
P
2
, 因此, P
L
V
P
2
2R
L
和
P
SUP
V
DD
I
DD
avg
和
I
DD
avg
1
0
V
P
R
L
sin(t) dt
1
V
P
R
L
[cos(t)]
0
2V
P
R
L
因此,
P
SUP
2 V
DD
V
P
R
L
(7)
效率 的 一个 BTL 放大器
V
P
2
2 R
L
2 V
DD
V
P
R
L
V
P
4 V
DD
P
L
= 电源 delivered 至 加载
P
SUP
= 电源 描绘 从 电源 供应
V
LRMS
= rms 电压 在 btl 加载
R
L
= 加载 阻抗
V
P
2 P
L
R
L
BTL
2 P
L
R
L
4 V
DD
在哪里:
因此,
V
P
= 顶峰 电压 在 btl 加载
I
DD
avg = 平均 电流 描绘 从 这 电源 供应
V
DD
= 电源 供应 电压
η
BTL
= 效率 的 一个 btl 放大器
(8)
TPA6011A4
SLOS392A–FEBRUARY2002–REVISEDJULY2004
figure38.voltageandcurrentwaveformsforbtlamplifiers
althoughthevoltagesandcurrentsforseandbtlaresinusoidalintheload,currentsfromthesupplyarevery
differentbetweenseandbtlconfigurations.inanseapplicationthecurrentwaveformisahalf-waverectified
shape,whereasinbtlitisafull-waverectifiedwaveform.thismeansrmsconversionfactorsaredifferent.
keepinmindthatformostofthewaveformboththepushandpulltransistorsarenotonatthesametime,这个
supportsthefactthateachamplifierinthebtldeviceonlydrawscurrentfromthesupplyforhalfthewaveform.
thefollowingequationsarethebasisforcalculatingamplifierefficiency.
substitutingplandpsupintoequation7,
table5employsequation8tocalculateefficienciesforfourdifferentoutputpowerlevels.notethattheefficiency
oftheamplifierisquitelowforlowerpowerlevelsandrisessharplyaspowertotheloadisincreasedresultingin
anearlyflatinternalpowerdissipationoverthenormaloperatingrange.notethattheinternaldissipationatfull
outputpowerislessthaninthehalfpowerrange.calculatingtheefficiencyforaspecificsystemisthekeyto
properpowersupplydesign.forastereo1-waudiosystemwith8-
Ω
loadsanda5-vsupply,themaximumdraw
onthepowersupplyisalmost3.25w.
26
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