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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.


locked by Kortuk Dec 4 '12 at 1:54

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It would be helpful if you posted a link to the circuit and if you gave us details of what you actually made. Circuit diagrams, detailed parts lists and pictures would help. Also, you should edit your account details and put your name there instead of signature. – AndrejaKo Dec 7 '10 at 17:17
If you put a P-ch FET in place of an N-ch FET, matching drain-source-gate to what the N-ch uses, it might explode as you would forward bias the body diode and conduct loads of current. Without knowing the circuit we can't tell. – Nick T Dec 7 '10 at 17:33
We need a "magic smoke" tag! :-) – Peter Loron Dec 8 '10 at 7:13
@PeterLoron Done. – mjh2007 Dec 8 '10 at 18:22
question is vague and should be closed w/o further information about the circuit. – Jason S Oct 10 '11 at 11:49

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.
Thanks Thomas O, very helpful. I'll look into your suggestions. – Windyfeller Dec 8 '10 at 8:54
Thanks to all for yourr suggestions. I will post a link to the circuit diagram as this might help others with the same interest too. – Windyfeller Dec 8 '10 at 9:07
4. The switching MOSFETs in SMPS are ok to reverse bias because the body diode is meant to conduct for zero-voltage switching, right? – endolith Jul 8 '11 at 21:59
@Endolith the body diode is very weak, typically less than 1/3rd the rating of the MOSFET, and it is very slow, so it's not much good. – Thomas O Jul 9 '11 at 0:14

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