Philips TDA1561Q - Manual (Page 7)

1997 Aug 14 7
Philips Semiconductors Preliminary specification
2
×
23 W high efficiency car radio power
amplifier
TDA1561Q
Heatsink design
There are two parameters that determine the size of the
heatsink. The first is the rating for the virtual junction
temperature and the second is the ambient temperature at
which the amplifier must still deliver its full power in the
BTL mode.
With a conventional BTL amplifier, the maximum power
dissipation with a music-like signal (at each amplifier) will
be approximately two times 5 W. At a virtual junction
temperature of 150
°
C and a maximum ambient
temperature of 60
°
C, R
th(vj-c)
= 1.3 K/W and
R
th(c-h)
= 0.2 K/W, the thermal resistance of the heatsink
should be:
Compared to a conventional BTL amplifier, the TDA1561Q
has a higher efficiency. The thermal resistance of the
heatsink should be:
150 60 –
2 5
×
---------------------- 1.3 – 0.2 – 7.5 K/W =
1.7
150 60 –
2 5
×
----------------------  
 
1.3 – 0.2 – 13.8 K/W =
Fig.3 Thermal equivalent resistance network.
handbook, halfpage
3.6 K/W
0.6 K/W
3.6 K/W
virtual junction
OUT 1 OUT 1
case
3.6 K/W
0.6 K/W
3.6 K/W
OUT 2 OUT 2
MGC424
0.1 K/W