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I have an N channel MOSFET and a P channel MOSFET. I found that for the P-channel MOSFET I need a heatsink that is lower than 5°C/W. The N channel MOSFET needs a heatsink that is lower than 13°C/W.

I have done quite a bit of research, but I don't know how I can figure out the proper heatsink for these two requirements. I have tried looking up datasheets for heatsinks, but I wasn't able to find any. Maybe heatsinks don't have datasheets. I'm not really sure.

How do I know how much heat a heat sink can handle? Where do you find this information?

Example: I found this heatsink on Amazon, but it says absolutely nothing about how much heat it can handle. How do I figure that out?

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    \$\begingroup\$ Amazon is not a good source of components. Heat sinks do have datasheets. Usually a technical drawing along with data about thermal resistance over air flow should be provided. \$\endgroup\$ Jun 9 at 7:28
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    \$\begingroup\$ Electronics distributors often have paramteric search that lets you search for exactly what you need. There you can for example search for 5C/W with or without forced air. Ifen if you don't buy there you are able to estimate what you'll be looking for. Also don't forget that you'll have a thermal resistance at the interface between the case of your device and the heatsink... \$\endgroup\$
    – kruemi
    Jun 9 at 7:51
  • \$\begingroup\$ And about the Amazon-Heatsink? That's probably (just looking at the size) in the range well above 40K/W with just convection. Lower with forced air. \$\endgroup\$
    – kruemi
    Jun 9 at 8:04
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    \$\begingroup\$ Here's a heat sink similar to the Amazon one: - 74°C/W nz.element14.com/fischer-elektronik/ick-smd-f-8-sa/… \$\endgroup\$ Jun 9 at 8:08
  • \$\begingroup\$ See this at the end ... you will find some answers about Rth (sorry, in french ... use google translate) sonelec-musique.com/electronique_bases_radiateur_calcul.html \$\endgroup\$
    – Antonio51
    Jun 9 at 12:41

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A heatsink from a reputable supplier will have a datasheet that tells you the degC per watt.

I don't blame you for wanting to use a cheap one without a datasheet, but your options for that are basically:

  • Use the specs from a similar name brand heatsink.

  • Use a bunch of thermodynamics to try to calculate the performance (not recommended, complicated and prone to being way off)

  • Test it yourself using thermometers and a constant wattage load.

One last thing, which it sounds like you may already understand is that heatsinks aren't rated for fixed amount of heat (like watts). The hotter your part can get, the more power the heatsink can dissipate. The heatsink would have a thermal limit too, but realistically it would be far higher than the part it's cooling so don't worry about it.

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