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Date: Tue, 14 Jan 2003 21:59:44 +0100
From: Rene Tschaggelar
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Subject: Re: Selecting a heatsink?
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Glenn Ashmore wrote:
> How do you properly size a heatsink for a MOSFET? What spec do you look
> at on the MOSFET data sheet to compare with the heatsink specs?
> For example: I want to run 6.5 amps through a MOSFET with a drain to
> source on resistance of .04 Ohms. I think the formula to get watts is
> I^2*R so I am generating about 1.7 watts. The thermal resistance is
> 2.2ēC/W junction to case and .5ēC/W case to sink for a total of 2.7ēC/W
> times 1.7 watts is 4.7ēC above ambient. Am I correct so far? That
> sounds mighty low.
> Assuming I got that right, what do you look for in heatsinks using
> natural convection?
You're right so far. Though 1.7W is not much.
Now you're looking at a heatsink with N*degC/W and that's it.
Add the temperatures.
As hints :
1W is about doable with a TO220 screwed onto a double sided pcb
with copper underneath on both sides.
10W is about the threshold for a fan, otherwise the sink becomes
big and heavy
100W requires a big noisy fan on big heatsink , better go to
liquid cooling here.
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
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