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Hi all. I successfully built the ZVS driver and amcurrently enjoying a good Jacob's ladder. Just one problem: one of the 2 FETs becomes terribly hot after a while. If I keep the thing on for more than a couple of minutes it burns. Since the ZVS circuit is simmetrical this seems very strange. I tried with 2 different flybacks with the very same result.
Yes, pretty symmetrical windings (not really perfect but good enough I hope). I thought the same thing, that's why I changed flyback. The strange thig is the other FET is hardly getting warm! This is driving me crazy. In the meanwhile I burned another IRFP250. I took them from 2 TV sets, so they might be DC. Weren't DC flyback supposed to be good for a ZVS drive? One of them is marked Grundig M29201
Registered Member #3766
Joined: Sun Mar 20 2011, 05:39AM
Location:
Posts: 624
They're DC unless the TV's were really, really old. Do they have air-gaps? Are the fet's insulated from each other? not sure if either of those would cause what you're seeing, but it couldn't hurt.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
AC flybacks are much better for push-pull drive like the ZVS circuit, but I've run DC ones too without any heating. Are you sure you wired it correctly? Are your diodes fast enough? Are all your components matched? Do you have a scope to look at the waveforms? Something is not right here.
I'm pretty scared at putting the probes from my oscilloscope at less than 2 meters from the ZVS! I checked the diodes, they seem OK. May any SLIGHT difference be the cause? I'll try to swap some of them to see if the other FET starts to heat up. I have no better idea! How can I check for the air gaps? I cant see any
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
So wind a different transformer on a ferrite core so you don't have HV in the picture. I've used the same circuit to produce much lower voltages with an appropriate transformer. Heck you don't even really need a secondary at all to test it.
Registered Member #3766
Joined: Sun Mar 20 2011, 05:39AM
Location:
Posts: 624
look along the ferrite core, it will be a little gap, bout the thickness of a piece of paper, lack of one could cause the transformer to do funky things, like walk itself into saturation, but listen to James, try it with a low voltage coil and scope it.
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