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smitten 9th June 2007 05:50 PM

Drivers and FETs destroyed, Help Please

I have designed a class D outputstage and it has worked perfectly untill today when I made a stupid mistake and destroyed it.

I am using irs20124s MOSFET drivers and IRLIB4343 MOSFETs in a full bridge configuration.

I had no load on the outout and was measuring the output signal by connection the probe to the upper mosfet source pins. I then moved the probe so I shorted the source and drain on the upper mosfet. Big sparks and the usual smell.

Since I shorted the upper fet i thought only the lower fet was destroyed and the problem isolated to on of the two complementary output stages(full-bridge). I then noticed that both drivers had a short between input and positive rail and also the buffer before the drivers was damaged. I use 10Ohm gate resistors.

If a fet is destroyed does the gate become connected to the drain? This could have damaged the driver connected to the mosfets i shorted. But how did the second driver get destroyed? It was not even connected to the other half side through a load. I just cant see how both drivers were destroyed.

Any ideas on this? Do you think I should just change both drivers and 4 FETs and try again or is there a resonable chance some can be reused?

BWRX 9th June 2007 06:33 PM

Re: Drivers and FETs destroyed, Help Please

Originally posted by smitten
If a fet is destroyed does the gate become connected to the drain?
Often, you will see a short between all three pins of a damaged MOSFET.

Just because there was no load connected doesn't mean there was no way for current to flow from one half bridge to the other. Both high side MOSFETs are connected to the same supply rail and both low side MOSFETs are connected to ground. The driver chips are both connected to ground and probably to the same Vcc supply as well. There are lots of strange ways current from one half bridge can end up flowing through the other.

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