Thursday, August 13, 2015


I first learnt about the heatsink in my early days with VU2LEX around 1994. He showed me the calculations for his cwtx. etc But somehow I never need the heatsinks seriously till I made the IRF640 LINEAR in 2014.

My success with linear is mostly attributed to the first big heatsink I found from flea wendor. It costed me about Rs40/- about half dollar a two years ago. It was a Pentium computer heatsink. Then I found few in Mumbai lamington roads flea vendors and then from my local markets. As such these are not normally sold in shops. But, there is a shop in Mumbai which specially sells the very big  heat sinks, but it will be costly for a single purchase. (will appraise its name later on)

Here are the pictures of various types of the heatsinks available with me ( I am not selling anything he he ... these are for all my upcoming linear projects/devices)
(will update the pictures on 14aug2015)
Empirical calculations for calculating the heatsink temperature.

Basic formula for temperature rise VS area VS power dissipation.

Say your area is 1 square inch and dissipation is 1 watt, ther temperature rise in C is 130 degrees C

increase area to 10 square inches and the temperature rise drops to 13 degrees

130 * (Watts / Square Inches)

How to calculate the required area of heatsink.

the formula you want to use is 130 degrees C / Watt / Square inch

So say you have 80 square inches and the amp will be about 50% efficient so 40 watts dissipation That will be 65 degrees C temperature rise making the heat sink 100 degrees C at 100% duty cycle. SSB is around 30% AM linear would be higher.

2 to 3 square inches of surface area for every watt of dissipation.

Fins vertical is the most efficient heat radiator

Fins up second best

Fins down useless without a fan.