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Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
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Posts: 635
After working on a full-bridge power supply for a shamefully long time, I believe I've isolated my transistors as the issue. When power is applied, my system is a dead short. I've moved to a half-bridge design for the sake of my limited silicon supply. After many interesting failures (from exploding pcb traces to a pinhole-size explosion through the casing strong enough to blast through a heatsink clip!), I decided to test what I had. I've exhausted my supply of IRFP240's, and am left with the stronger IRFP460's and some IRF740's. I want to run my system from 350-400kHz, which I know the 740's should be able to do. But after finding my system was yet again, an effective short (this time, ballasting it with a 1k resistor, and running from a battery...) I decided to test the FETs individually. I did this by attaching one to my GDT signal (which is quite clean) and then used my trusty 1k resistor as a load. I tested the waveform across the resistor and FET and found terrible waveforms even in the 200kHz region. They would not even turn off as I got closer to 400kHz. What do you guys think is going on? Am I the biggest sucker for EBAY FET counterfeiters? Is it possible that my o'scope is wrong about the frequency? Is my means of testing off? Thanks!
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Slow FETs?
