How To Select a Heat Sink
Example B
Example A
Find a space saving heat sink to keep a TO-220 device below the
maximum 150°C junction temperature in natural convection. Device
will be screw mounted with an electrically conductive interface.
Find a heat sink to keep a TO-220 device below the maximum
150 °C junction temperature in forced convection at 400 ft/min.
Device must be electrically insulated and mounted with a labor
saving clip.
Given:
P
R
= 6 watts
Given:
D
= 3°C/W (from semiconductor manufacturer)
P
= 12 watts
θJC
D
T max = 150°C (from semiconductor manufacturer)
R
= 2.5°C/W (from semiconductor manufacturer)
θJC
J
T
max = 65°C
T max = 140°C (from semiconductor manufacturer)
A
J
T
max = 50°C
A
A KonduxTM pad is a good choice for electrically conductive
applications.Thermal resistance for KonduxTM can be determined
from the following graph.
A Hi-Flow® pad works great with clip mounting and provides the
necessary electrical insulation.Thermal resistance for
Hi-Flow® at low pressure is 1.15°C/W (from page 87).
Typical TO-220 Performance
0.60
Using equation 1, solve for R
θSA
0.50
0.40
0.30
0.20
0.10
0.00
R
= 140 – 50 - (2.5 + 1.15) = 3.85°C/W
12
θSA
Many styles are available. If board space is a concern,
533202B02551G (pg 55) meets the requirements.
0
1
2
3
4
5
6
Screw Torque (in-lb)
Air Velocity—Feet Per Minute
0
200
400
600
800
1000
10
At 2 in-lb of torque the thermal resistance
is approximately R = 0.5°C/W
100
80
θCS
8
60
6
Using equation 1, solve for R
θSA
40
4
2
0
20
0
R
= 150 – 65 - ( 3 + 0.5) = 10.7°C/W
θSA
0
2
4
6
8
10
6
Heat Dissipated—Watts
53320X
53330X
The Index by Heat Sink Style on page 8 lists space saving heat sinks.
Several models are in the 10 °C/W range. Choose the one that best
fits the application and verify thermal resistance from graph.
According to the above graph, an airflow of 400 ft/min results
in a thermal resistance of 3°C/W.This is less than the required
thermal resistance of 3.85°C/W and is therefore acceptable
under these airflow conditions.
Part number 593202B03500G shows
a 60 °C temperature rise at 6 watts.
Air Velocity—Feet Per Minute
If height is a concern, 533702B02552G would meet the
requirements and is only 1.0” tall
0
200
400
600
800
1000
10
100
80
8
6
4
60
Hi-Flow®is a trademark of the Bergquist Company
40
2
0
20
0
0
2
4
6
8
10
Heat Dissipated—Watts
R
= 60 = 10.0°C/W
6
θSA
Which meets the above requirement in natural convection.
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