How To Select a Heat Sink
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.
Example B
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:
PD = 12 watts
R
θJC
= 2.5°C/W (from semiconductor manufacturer)
TJ max = 140°C (from semiconductor manufacturer)
TA max = 50°C
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).
Using equation 1, solve for R
θSA
R
θSA
= 140 – 50 - (2.5 + 1.15) = 3.85°C/W
12
Many styles are available. If board space is a concern,
533202B02551G (pg 55) meets the requirements.
Air Velocity—Feet Per Minute
400
600
800
HOW TO SELECT A HEAT SINK
Given:
PD = 6 watts
R
θJC
= 3°C/W (from semiconductor manufacturer)
TJ max = 150°C (from semiconductor manufacturer)
TA max = 65°C
A Kondux
TM
pad is a good choice for electrically conductive
applications. Thermal resistance for Kondux
TM
can be determined
from the following graph.
Typical TO-220 Performance
0.60
0.50
(ºC/W)
CS
R
0.40
0.30
0.20
0.10
0.00
0
1
2
3
4
Screw Torque (in-lb)
5
6
80
60
40
20
0
0
2
4
6
Heat Dissipated—Watts
8
10
8
6
4
2
0
Using equation 1, solve for R
θSA
R
θSA
= 150 – 65 - ( 3 + 0.5) = 10.7°C/W
6
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.
Part number 593202B03500G shows
a 60 °C temperature rise at 6 watts.
0
100
Mounting Surface Temp
Rise Above Ambient—°C
80
60
40
20
0
0
2
4
6
Heat Dissipated—Watts
8
10
200
Air Velocity—Feet Per Minute
400
600
800
1000
10
8
6
4
2
0
53320X
53330X
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.
If height is a concern, 533702B02552G would meet the
requirements and is only 1.0” tall
Hi-Flow® is a trademark of the Bergquist Company
R
θSA
= 60 = 10.0°C/W
6
Which meets the above requirement in natural convection.
10
AMERICA
EUROPE
www.aavidthermalloy.com
Thermal Resistance From MTG
Surface to Ambient—°C/Watt
USA
Tel: +1 (603) 224-9988 email: info@aavid.com
Italy
Tel: +39 051 764011 email: sales.it@aavid.com
United Kingdom
Tel: +44 1793 401400 email: sales.uk@aavid.com
ASIA
Singapore
Tel: +65 6362 8388 email: sales@aavid.com.sg
Taiwan
Tel: +886(2) 2698-9888 email: sales@aavid.com.tw
Thermal Resistance From MTG
Surface to Ambient—°C/Watt
Mounting Surface Temp
Rise Above Ambient—°C
At 2 in-lb of torque the thermal resistance
is approximately R
θCS
= 0.5°C/W
0
100
200
1000
10
AAVID [ AAVID THERMALLOY, LLC ]
