# Calculation of heatsink

Joined Feb 27, 2008
104
can any one help me out in calculating heatsink area. am using offline SMPS switcher IC.calculated junction temperature seems to be higher than the value mentioned in the datasheet. so external heatsink is required.now how to choose the area of required heatsink?

#### Lembit

Joined Nov 13, 2007
4
the simplest estimation is 10cm2 per avg W. It will do at room temperature, but a lot depends on your overall design of chassis etc.

#### sudharshan

Joined Mar 3, 2008
11
Avg watt means Watt. Give me an Example

#### scubasteve_911

Joined Dec 27, 2007
1,203
He is saying that every 10 square centimeters, you can dissipate a watt. This is just a rule of thumb though, so if it is critical, then over-rate your heatsink according to the rule, or you will have to do some finite element modeling.

A simple hand calculation doesn't lend itself to such a task. This is why heatsinks are spec'd given their thermal resistance in degrees/watt.

Steve

#### John Luciani

Joined Apr 3, 2007
477
can any one help me out in calculating heatsink area. am using offline SMPS switcher IC.calculated junction temperature seems to be higher than the value mentioned in the datasheet. so external heatsink is required.now how to choose the area of required heatsink?
You need to look at the heatsink thermal resistance. Also can you use a fan in your
application? How much can you afford to spend on a heatsink?

You can purchase a heatsinks with a wide variety of fin arrangements. The
purpose is to maximum the cooling surface area. Go to the heatsink manufacturers
website and look at the thermal resistance specifications.

Does the IC manufacturer have a heatsinking application note?

(* jcl *)