mosfet gate drivers? Do they usually fail when transitor fails?

[fastline]

I guess questions are above. Have a known shorted mosfet. Just curious if I need to worry about other component problems and what I am looking for.

 

[shrtrnd]

You really need to consider your circuit. Any device failing could cause another device to fail in the circuit. There's no guaranteed, always true, answer. I never assume a single device is the problem (although it frequently is), I always look for what's connected to the failed device, and make sure nothing else is wrong. So that when I replace the failed device, it doesn't just fail again.

 

[fastline]

So what is typically used for the gate driver of a mosfet? Basically it seems that there is a series 220ohm resistor in series to the gate, then goes to a daughter board with 1 TO-92 size transistor and a bunch of resistors.

 

[trobbins]

If you have tested the fet and it is showing (for example) a short between gate and drain, then should attempt to identify the peak current level that could pass into the gate circuit and what it would flow through. That may then suggest that certain parts would have been stressed to the point of destruction, and you may be able to gauge which parts would have been first to fail (eg. 220R resistor). You may be able to measure some of those parts (eg. resistor), and if they havn't failed then that may suggest that other parts are likely still fine. You have to check mac device ratings.

 

[shrtrnd]

And to add to what trobbins said, a higher current through the 220 ohm resistor, would just about guarantee the transistor in line with it was subjected to an overcurrent (and would probably be damaged).
I'd be looking at that transistor, as well as your gate driver.
I can't see the circuit, I'm just giving you the low-down on what I'd do, from what you've said so far. Trace the circuit, and look for anything that may have CAUSED your driver failure.

 

[(*steve*)]

If that circuit is surface mount, then beware that a marking of 220 on a resistor is actually 22 ohms, a value that is quite reasonable in a circuit where the gate current is significant (i.e. where fast switching is required).

If this is the same board that your shorted mosfet came from, then the driver may have been exposed to voltages and currrents beyond its wildest nightmare and certainly may have been damaged.

 

[NickS]

I vote yes as well. When working on an high power generator we went through a period of FET failures and they almost always would fail as short from gate to source and Drain to Source which would usually bring down the gate driver(and several other parts) at the same time. The worst part was when we thought surrounding parts were ok and didn't replace them. Then we would inevitably experience intermittent problems later on that were a result of damaged but not completely failing parts specifically FET drivers, series resistors and diodes.

My policy in the event of a massive part failure is replace everything that that part could have brought down in its failure. A major pain but to me its worth it.