Fan selection

[Electronics4you]

Hi there,

I have a circuit with four power MOSFETs. Near them (or on the heat sink) is placed a temperature sensor, which detects when the temperature is above a certain level. Now for the tricky bit...

How do a select the right fan/heat sink for the application?

I know the effect of the MOSFETs
I want to calculate the fan flow which is needed to cool down the MOSFETs faster than they heat up, so they don't cook.

 

[Russlk]

Unless you have applicable data on the heat sink, you will have to experiment.

 

[Electronics4you]

Do I need total area, thermal resistance, material...?

 

[Russlk]

Do I need total area, thermal resistance, material...?
No, you just have to make measurments and collect data.

 

[audioguru]

You just need the datasheet info for the heatsink, unless you made the heatsink by accident. You also need the datasheet info for the Mosfets.

 

[kchriste]

Do I need total area, thermal resistance, material...?

Yes, and how much power will be dissipated by the MOSFETs (worst case), the max junction temp for the MOSFETs, any airflow restriction and what the working ambient temperature range will be. It can be pretty complicated and it is usually easier to determine this experimentally.

 

[Electronics4you]

Yes I know I need all that datasheets, but how do I calculate it?
I have no idea
Have you any examples?

 

[kchriste]

A quick Google of "heatsink design" turned up this:
**broken link removed**
And this:
http://www.flomerics.com/flotherm/technical_papers/t226.pdf