Electronics > Beginners
Blown mosfet : I don't know why
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ratatax:
Hi

I use a P-channel mosfet for polarity protection in my circuit (an AO3407 http://www.aosmd.com/pdfs/datasheet/ao3407.pdf)  it's super simple :



Works great, I draw about 1A at 12V and it doesn't get hot.

However when i was doing some tests it suddently smoked. It still allows current to flow, but has a small burn mark close to the Gate pin. I was just probing some things on a totally unrelated part of the circuit, and I'm pretty sure I didn't do any short circuits, in fact my circuit kept running after that....

Bad part ? Is it possible that ESD causes this ? Is there a way to make it more sturdy, for safe use in a consumer product ? I'd like to understand what happened  :o
ratatax:
From https://www.4qd.co.uk/docs/mosfet-failure-mechanisms/ :


--- Quote ---The cause of this failure is a very high voltage, very fast transient spike (which may be positive or negative going). If such a spike gets onto the drain of a MOSFET, it gets coupled through the MOSFETs internal capacitance to the gate. If enough energy gets coupled, the voltage on the gate rises above the maximum allowable level – and the MOSFET dies instantaneously. The process takes less than a nano-second! The initial spike destroys the gate-body insulation, so that the gate is connected to the body. Once that has happened, the MOSFET explodes in a cloud of flame and black smoke. We have one documented case where the battery wire worked loose, causing a spark. It must have been this that caused the gate breakdown for the explosion of flame and smoke did not happen until the battery wire was re-connected some time later! Which demonstrates how very difficult cause and effect can be to connect!
--- End quote ---

I think that's was happened here, I often plug/unplug the power supply wires to do some tests, I noticed it had a small spark the last time I plugged it in, then the next time i powered it on it smoked.
But I'm not entirely sure how I prevent that. By adding a resistor on the gate ?
MagicSmoker:
Deleted because wrong. Oops. That'll teach me to dash off a quick reply.
ratatax:
I'm confused, most websites show the load connected to the Source and it works fine as i tested it.

But some adds a resistor to the gate, or even a zener sometimes to prevent overvoltages
tboy:
According to:
https://www.infineon.com/dgdl/Reverse-Batery-Protection-Rev2.pdf?fileId=db3a304412b407950112b41887722615
You have it wired correctly.  A better MOSFET symbol in your schematic would be a plus.  :)
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