# Shared Heat Sink

Discussion in 'General Electronics Discussion' started by NiGHTS, Jan 9, 2015.

1. ### NiGHTS

24
1
Nov 19, 2014
I am constructing a device that drives a load of about 2.5 Amps. The design involves a pair of MOSFETs and a voltage regulator. According to my calculations it would take 4 voltage regulators in parallel (with load balancing components) with complimentary heat sinks rated at most to 6.2 C/W thermal resistance to drive this circuit without overheating. Along with the MOSFETs, it would mean installing 6 large heat sinks for each TO-220 part. The device requires no moving parts, therefore a fan is not an option.

I am interested in consolidating space by using a single long heat sink instead of 6 individual ones. Problem is I don't know how to calculate the thermal resistance for a shared heat sink like this.

The thermal resistance requirement for the heat sinks are up to 6.2 C/W x 4 and 4.1 C/W x 2. I found a shared plate with a rating of 3.9 C/W that can hold all these parts. Is this good enough? I don't know whether I should average out these ratings or add them together.

Thanks again for your help guys!

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,849
Jan 21, 2010
In this case the answer is pretty simple. You need a single heatsink with a thermal resistance of about 1 degC/W and you need to space the devices out evenly along it.

In a more complex case you treat it like resistors in parallel. So if you required a 10 degC/W, a 4 degC/W and a 15degC/W heatsink, you could combine them on a single heatsink of 1/ (1/10 + 1/4 + 1/15) degC/W = 2.4 degC/W.

This too is a simplification, but if you have used the same assumptions about temperature and you are using similar packages then is should be close enough. I always advise being conservative in your calculations so that any small differences will be easily absorbed by the extra leeway you give the devices.

3. ### NiGHTS

24
1
Nov 19, 2014
Thank you for your help Steve. Your formula gives me the tool I need to approximate my requirements.

Since I can't find any heat sinks lower than 2.9 K/W I'll have to find another way to deal with my heat problem.

4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,849
Jan 21, 2010
Here is a 0.78 degC/W heatsink. This is what I used for my dummy load. They do exist. This one is perfect for placing several components along its length.

Here is another one that is even easier to mount devices to.

Similar heatsinks must be obtainable elsewhere.

Edit: Sorry I lie. The one I used was 0.37 degC/W -- here.

Last edited: Jan 11, 2015