What actually kills MOSFETs?

[FPS]

When used to drive transformer primaries, MOSFETs often die when used within their rated specs, they should be able to handle that voltage/current at least on paper.  Is this effect analogous to mismatched antennas on radio transmitters?

[AstRii]

MOSFETs often die when used within their rated specs

If you're only looking at datasheet specs like their rated voltage and current, then yes. However there is so much more information in the datasheet which is often overlooked. Perhaps most importantly:


The fact that a MOSFET can handle 500V at 100A, doesn't mean it will handle it however you like. There are limitations to how long and how often can a MOSFET take such abuse.

Thermal capabilities also cannot be overlooked! If you're using a large heatsink it doesn't necessarily mean that the chip temperature cannot reach over 150C.

In my experience; in hobbyist electronics MOSFETs die mostly due to people not paying sufficient attention to datasheet or wrong circuit design. Where as in consumer electronics, MOSFETs die most often due to poor thermal contact between the FET and heatsink.

[unrealcrafter2]

I personally find MOSFETs die from sudden spikes in voltage. Especially on the gate. It is possible to overheat them too, especially if it's not heatsinked.