A Tale Of 4 Broken Fets

It was the best of times, it was the worst of times, so is the winter of discontent, hay fever and corona virus. Today i have been playing with this amp board i designed a whole ago and have had sitting here until i could be interested enough to actually drag it out and populate it. And today that is exactly what i did.

Nothing revolutionary here, its IRF510’s in a 2×2 push pull configuration. VCC = 24v, Drive = 5W there is some negative feedback and all the usual goodies. So with everything connected up, i turned down the current limit on the power supply just to be sure to be sure, turned on the supply and slowly began to increase the current.

The scope was saying 40v rms and I think to myself that is about 35W. I should be doing more than that with the amount of drive and current being drawn, but I left the PSU in current limited and i was playing it safe. I look at the Swarez meter and its showing 35W.
So i open the taps and give her all the current she has got. I look at the scope 200V p-p thats 100W and the Swarez meter only showing 35W. 3 minutes later BOOM all the fets let go. Checked the Swarez meter, it was in the 2Kw range, not 200W range, I was doing 100W and the heatsinks on both the amp and the dummyload were toasty warm.
So, to much bias, to much drive and ultimately to much current. But I should be able to turn this down to a nice 50W and it will kick along without much drama.

The End.

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