TDA8947J anfi devresi (2x25w 1x50w) - 320Volt

Philips Semiconductors
TDA8947J
4-channel audio amplifier
13.3 Thermal behavior and heatsink calculation
The measured maximum thermal resistance of the IC package, R th(j-mb) , is 1.3 K/W.
A calculation for the heatsink can be made, with the following parameters:
T amb(max) =60°C (example)
V CC = 18 V and R L =4Ω (SE)
T j(max) = 150 °C (specification)
R th(tot) is the total thermal resistance between the junction and the ambient including the
heatsink. This can be calculated using the maximum temperature increase divided by the
power dissipation:
R th(tot) =(T j(max) − T amb(max) )/P D
At V CC = 18 V and R L =4Ω (4 × SE) the measured worst-case sine-wave dissipation is
17 W; see Figure 9. For T j(max) = 150 °C the temperature raise, caused by the power
dissipation, is: 150 °C − 60 °C =90°C:
P × R th(tot) =90°C
R th(tot) = 90/17 K/W = 5.29 K/W
R th(h-a) =R th(tot) − R th(j-mb) = 5.29 K/W − 1.3 K/W = 3.99 K/W
This calculation is for an application at worst-case (stereo) sine-wave output signals. In
practice music signals will be applied, which decreases the maximum power dissipation to
approximately half of the sine-wave power dissipation of 9 W (see Section 8.2.2). This
allows for the use of a smaller heatsink:
P × R th(tot) =90°C
R th(tot) = 90/9 K/W = 10 K/W
R th(h-a) =R th(tot) − R th(j-mb) = 10 K/W − 1.3 K/W = 8.7 K/W
9397 750 14938 © Koninklijke Philips Electronics N.V. 2005. All rights reserved.
Product data sheet Rev. 02 — 16 June 2005 18 of 24