This if a fairly simple question. I have some APT43M60L MOSFETs with a fairly high on resistance. They get quite hot and waste a lot of power in my induction heater. They work great but get really hot really quick. I tried IRFP250M MOSFETs, they also worked great, but I just needed a little more power.
We all know that putting 2 identical (or near identical) resistors in parallel halve the resistance. For example, two 1k resistors in parallel would make 500 Ohms.
So does this concept apply to parallel MOSFETs? Could I simply put 2 of these APT43 MOSFETs in parallel to lower the on resistance without any drawbacks?
Best Answer
Yes. It does. Note that in general you can't blindly parallel transistors. You can parallel MOSFETs without special measures since as they get hotter they conduct less well which distributes the load more or less evenly in spite of individual component differences. Positive temperature coefficient.
BJTs conduct BETTER as they get hotter so the BJT that conducts best conducts even more in a positive feedback loop until it is conducting the entire load and fries while the other parallel BJTs conduct nothing (unless you take special measures such as load balancing resistors). Negative temperature coefficient.
Then there are IGBTs that where the temperature coefficient changes between positive and negative so if you run it at the right operating point, you can parallel them but if you don't run it at the right operating point it will fry (unless you take special measures).
The drawback is there is now more total gate capacitance/charge so the MOSFETs will take longer to turn on and off for the same gate drive which matters if you're switching at high frequency.