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Registered Member #54655
Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82
Hi guys, are these MOSFETS suitable for sstc duty? I ordered 6 of them and have been trying to use them for a single MOSFET sstc. So far I've blown 3 of them and I can't figure out what I'm doing wrong. The third one was just hooked up to a function generator for the gate drive, an 18 volt battery, and a 5 turn primary coil driving a roughly 600khz secondary. It worked for about 10 seconds and then just stopped. The fet was cold when it died and measured short circuit across all terminals. I bought the fets from digikey so they should be good. Any help is greatly appreciated.
Registered Member #55205
Joined: Mon Jun 08 2015, 06:06AM
Location:
Posts: 15
I've been having a similar prob with my HF 1250v 30a IGBT's 6 died of 8 bought. Last 2 are safe in a Mazzilli ZVS driver, and work flawlessly there.
In my case, they were rated for Soft-Commutation ONLY, and I believe I was getting some hard switching due to freq. mismatch. Yet they all remained cool to touch, and 2 even died at 12v for testing. In Single, and Half-Bridge configs... All bought through Mouser NEW.. Frustrating, considering they were priced fair, and perform flawlessly in the ZVS..
Do you also have a S -> D fast/ultra fast diode? Inrush current also killed a couple of mine, Do you have anything for that? Ballasting with a 700w MOT primary helped me last a bit longer when going off 120v mains..
Could also just be a bad die-lot, 1 of mine was D.O.A. I'd like to know if you get it figured out though, as we probably have similar issues..
Registered Member #54655
Joined: Thu Mar 19 2015, 05:56PM
Location: BC, Canada
Posts: 82
That sounds exactly like my problem. They have a fast (160ns Trr) internal diode, so I thought that they wouldn't need an external diode. I don't have anything for current limiting either. These ones are a brand new product though, they could be a bad lot? Still they shouldn't have died on 18 volts. An irfp460 would have done better!
Registered Member #55205
Joined: Mon Jun 08 2015, 06:06AM
Location:
Posts: 15
I'd try putting an Ultrafast diode in there Source -> Drain .. "Fast" 'should' be ok as well. I've been taught to ignore the internal ones (outside of LV stuff). Maybe remove the TVS and try Anti-P. Zeners?
What kind of driver are you using? Is it interrupted or just a 555? If so, try inverting the signal, or a 2 winding gdt flipping the secondary leads(what I'm doing now) when/if using secondary feedback.
I'm still pretty newb myself, but have been paddling that very same boat for a while.. lol Those are just some things I found made things a bit easier. Especially the 2 wire GDT.
If they're not getting hot but they're dying it's almost always an overvoltage issue. Just because you only placed 18V on the drain doesn't mean that's all that is going to be there. When operating an inductive load with a single ended configuration you get reflected flyback spikes whenever the switch opens up. I've personally observed a 12V supply cause spikes well over 400V.
My advice: use an external fast antiparallel diode rated for very high voltage, and consider placing a flywheel one across the primary. Other than that you can attempt Class-E configuration.
Registered Member #55205
Joined: Mon Jun 08 2015, 06:06AM
Location:
Posts: 15
Sigurthr wrote ...
If they're not getting hot but they're dying it's almost always an overvoltage issue. Just because you only placed 18V on the drain doesn't mean that's all that is going to be there. When operating an inductive load with a single ended configuration you get reflected flyback spikes whenever the switch opens up. I've personally observed a 12V supply cause spikes well over 400V.
My advice: use an external fast antiparallel diode rated for very high voltage, and consider placing a flywheel one across the primary. Other than that you can attempt Class-E configuration.
You say to use Anti P. for the external Fast diodes? I've been using singles, I suppose thinking about it, it would also catch the negative spikes?
Antiparallel isn't a type of diode, you're thinking of TVS (which would be "two in series, anode center, parallel to device"), it's a way of stating which direction to place it; anode to source, in parallel with device.
Registered Member #55205
Joined: Mon Jun 08 2015, 06:06AM
Location:
Posts: 15
Sigurthr wrote ...
Antiparallel isn't a type of diode, you're thinking of TVS (which would be "two in series, anode center, parallel to device"), it's a way of stating which direction to place it; anode to source, in parallel with device.
Gotcha.., thanks for clarification, I had assumed Anti-P. was the configuration: "two in series, anode center, parallel to device"; not the direction in which it is placed.
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I keep blowing these MOSFETS
