Why did the MOSFET explode

mosfettroubleshooting

I'm new here, and I'm new to electronics. I have a keen interest in building a wind powered battery charger and I'm having a crack at the charge controller. I found a circuit that is published free on the 'net and after a few false starts and blind alleys I finally finished my charge controller- or so I thought! My mosfet exploded (well,it went pop and split apart really but it surprised me).

Can anyone tell me what I might have done wrong? Will it have damaged any other components on the board?

If it helps, its an IRF9520 P channel mosfet. I'm not sure whether it should have been an N channel – would this have caused the problem?

Grateful for any help or advice.

Best Answer

Some things that can make a MOSFET pop:

  • Too high Vds voltage, i.e. a 20V MOSFET on a 24V system wouldn't last long.
  • Exceeding power dissipation (could be a short circuit, but can also be due to very high frequency switching. If you're not using a SMPS, this probably isn't relevant.)
  • Exceeding Vgs(max), which is usually ±20V. This is quite a common failure leading to the breakdown of the delicate gate insulator.
  • Reverse biasing the drain and source making the body diode conduct (as Nick T mentioned.)
  • Mechanical stress can cause bonding wires to fail or short to places they shouldn't, but this is rare.
  • If you mounted it on a heatsink remember that the tab of the MOSFET is connected to a pin, usually source, but sometimes drain. If you grounded the heatsink it could cause Bad Things to happen.
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