Datasheet
V
(LRMS)
V
O
I
DD
I
DD(avg)
Efficiency of a BTL amplifier +
P
L
P
SUP
where:
P
L
+
V
L
rms
2
R
L
, and V
LRMS
+
V
P
2
Ǹ
, therefore, P
L
+
V
P
2
2R
L
P
L
= Power delivered to load
P
SUP
= Power drawn from power supply
V
LRMS
= RMS voltage on BTL load
R
L
= Load resistance
V
P
= Peak voltage on BTL load
I
DD
avg = Average current drawn from the
power supply
V
DD
= Power supply voltage
η
BTL
= Efficiency of a BTL amplifier
and
P
S
UP
+ V
DD
I
DD
avg
and
I
DD
avg +
1
p
ŕ
p
0
V
P
R
L
sin(t) dt
+ *
1
p
V
P
R
L
[cos(t)]
p
0
+
2V
P
p R
L
Therefore,
P
SUP
+
2 V
DD
V
P
p R
L
substituting P
L
and P
SUP
into equation 6,
Efficiency of a BTL amplifier +
V
P
2
2 R
L
2 V
DD
V
P
p R
L
+
p V
P
4 V
DD
V
P
+ 2 P
L
R
L
Ǹ
where:
(10)
TPA6205A1
SLOS490B–JULY2006–REVISEDJUNE2008..............................................................................................................................................................
www.ti.com
Aneasy-to-useequationtocalculateefficiencystartsAlthoughthevoltagesandcurrentsforSEandBTL
outasbeingequaltotheratioofpowerfromthearesinusoidalintheload,currentsfromthesupply
powersupplytothepowerdeliveredtotheload.ToareverydifferentbetweenSEandBTL
accuratelycalculatetheRMSandaveragevaluesofconfigurations.InanSEapplicationthecurrent
powerintheloadandintheamplifier,thecurrentandwaveformisahalf-waverectifiedshape,whereasin
voltagewaveformshapesmustfirstbeunderstoodBTLitisafull-waverectifiedwaveform.Thismeans
(seeFigure34).RMSconversionfactorsaredifferent.Keepinmind
thatformostofthewaveformboththepushandpull
transistorsarenotonatthesametime,which
supportsthefactthateachamplifierintheBTL
deviceonlydrawscurrentfromthesupplyforhalfthe
waveform.Thefollowingequationsarethebasisfor
calculatingamplifierefficiency.
Figure34.VoltageandCurrentWaveformsfor
BTLAmplifiers
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