pfc mosfet fail
First of all you need to understand if the power dissipation is within the design limits. If it is, then you will look at ways to decrease it (although you should have allowed for an adequate heatsink in the first place, if you knew the power dissipation).
If it isn't, then you need to understand what makes the MOSFET dissipate more:
- is the MOSFET driven fully on?
- is the switching frequency correct?
- is the inductor sized correctly? does it by any chance saturate?
- is the Rdson of the MOSFET low enough?
- is the diode adequate for PFC use?
- did the MOSFET fail because of power dissipation, really? are the Vds voltage and Id within limits? do you have adequate margin, especially for Vds?
If everything seems OK, then look for ways to decrease the power dissipated in the MOSFET:
- use a MOSFET with lower Rdson (or two MOSFETs in parallel).
- use lower switching frequency if possible
- use a gate driver to speed up the MOSFET
Failing all that, consider forced-air cooling.
Hope this helps.