Philips Semiconductors
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TDA1562Q application note
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© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
Application note
Rev. 01.02 — 05 May 2006
34 of 62
The curves in figure 18 do not show the advantage in power dissipation the TDA1562Q
has when it is driven with a music signal. This advantage can only be illustrated by
measuring the power dissipation with a music signal or a music-like signal, as it is done
in fig. 19.
A: Class AB amplifier
B: TDA1562Q
Fig 19. Power dissipation with IEC 60268 filtered pink noise
When the power dissipation is measured with a music-like signal, it is very clear that the
TDA1562Q has a great advantage over a conventional class AB amplifier. Only at
extremely high levels, when the amplifier is clipping very heavily, the power dissipation
will equal that of the class AB amplifier.
To calculate an appropriate heatsink for the amplifier, it is necessary to know the power
dissipation. As already mentioned, for class AB amplifiers this is usually done by
measuring the worst case power dissipation with a sine wave signal and then taking 50%
of that value as a value for the power dissipation with music.
From fig. 18 we can see that in this case the worst case power dissipation for the class
AB amplifier is 35W, so the heatsink should be calculated for a power dissipation of
17.5W. The next step is to take this result to the curves measured with the noise signal
(fig.19). When we draw a line down from the point where the power dissipation in the
class AB amplifier is 17.5W to the curve of the TDA1562Q, we see that at that output
level the power dissipation of the TDA1562Q is only 9.3W. this means that the heatsink
for the TDA1562Q can be considerably smaller than that of the normal class AB
amplifier.
TDA1562Q Pdiss vs Pout
0
10
20
30
0
10
20
30
40
50
Po(W)
Pd(W)
A
B
IEC 60268 filtered pink noise
Rload = 4ohms
clip level
17.5W
9.3W