Electronics > Beginners

Mosfet gate breakdown survivable?

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justinjja:


This circuit was running fine at 30v, when cranked up to 35v the pnp transistor and p channel mosfet both started over heating,
realized I'm missing a resistor under the first 2N5551.

Do you think I damaged the mosfet by breaking down the gate?
I shut it down before it got too hot. (magic smoke still in side...)

amyk:
That part you're using only has a 20V Vgs. If it survived it would probably die soon.

In any case a blown gate is definitely not "survivable", and you can check by measuring with a multimeter.

T3sl4co1l:
You only need 10V.  Put a e.g. 12V zener (1N5242 say) in parallel with the pull-up resistor, and don't omit the emitter resistor of the first transistor.

Also, move the series resistor to between the emitter follower and MOSFET gate.  Use a smaller value like 47 ohms.  This dampens possible oscillations.

Tim

justinjja:
Mosfet is fine currently, Just wondering if is going to fail soon.

Actually a resistor after the emitter doesn't work, Needed to use 2 series resistors before the collector as a voltage divider.
And the 500R series resistor is gone now.

Thanks,
Justin

T3sl4co1l:
You probably used the wrong values then.  This is the preferred method:



Note the input voltage is logic level (0 and 5V) only, and the resistor ratios, and zener diodes used.

Note also this is a rather inefficient method, especially if you're going to be cranking it up to 80V.  Just use a high side gate driver chip like IR2101, and don't waste time with poor-performing P-channel FETs.

Tim

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