RDAG12-8 Manual
The heatsink temperature of the amplifier supplying .250A at 5V DC can reach100
E
C. max (measured at
ambient room temperature of 25
E
C). The power dissipated by the amplifier is (12-5)x.250 = 1.750W.
The maximum allowed junction temperature is 125
E
C. Assuming the junction-to-case and case-to-heat
sink surface thermal resistance for the TO-220 package is 3
E
C/W and 1
E
C/W respectively. The junction-
JHS
0-heat sink resistance R
=4
E
C/W. The temperature rise between the heat sink surface and the junction
is 4
E
C/W x1.75W=7
E
C. Thus the allowed maximum temperature of the heat sink is 125-107=18
E
C.
Therefore if any of the channels of the RDAG12-8 has a 250mA load the ambient temperature rise is
limited to 18
E
C. The allowable maximum ambient temperature will be 25 +18=43
E
C.
If forced air cooling is provided then the following calculation will determine the allowable load for the
RDAG12-8 allowable power dissipation for the power amplifier:
amb.max
max
HS
JHS
P
= (125
E
C-T
)/
(R +R
) where
HS
Heatsink thermal resistance R
= 21
E
C/W
JHS
Junction- to-heatsink surface thermal resistance R
= 4
E
C/W
Operating temperature range
= 0 - 50
E
C
am b.m ax
Maximum ambient temperature T
= 50
E
C
max
At air velocity of <100 ft/min
P
= 3W
max
At air velocity of 100 ft/min
P
= 5W
(As determined by the heat sink
characteristics )
Page B-2
Manual MRDAG12-8H.Bc2