(3)
Heat Radiation Balance
The heat produced in the IC is radiated to ambience through the package and the heat
sink.
The quantity of the heat radiation depends on the heat source temperature, ambient
temperature and the thermal resistance of the package.
(3-1)
TO-220 with heat sink
Heat radiation balance model of the TO-220 with heat sink is shown as below.
P
LOSS
θ
JC
θ
CH
θ
HS
Tj
Heat Source
(junction)
Temperature
θ
JS
Ambient
Temperature
Ta
Where
θjc
:
θjs
:
θ
CH
:
thermal resistance between IC chip (junction point) and the
package backside connecting to the heatsink.
thermal resistance between IC chip (junction point) and the
package surface.
thermal resistance between package backside and the heat sink
including the condidtion of insulator, silicon grease and
tighten torque.
thermal resistance of the heat sink
Package
Face Side
Resin
Chip
Package
Back Side
θ
HS
:
θ
JS
θ
JC
θ
CH
θ
HS
IC
Heat Sink
If the js is large enough compare with other thermal resistance, the js can be neglected and the
heat radiation model can be mentioned as below.
P
LOSS
θ
JC
θ
CH
θ
HS
Tj
Ta
The relation between temperature and heat radiation quantity is shown below.
Tj=P
LOSS
X (θjc+θ
CH
+θ
HS
) + Ta
(℃ )
Page 9 of 10
MICRO-ELECTRONICS [ Micro Electronics ]
