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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I've had a slew of problems with my little SSTC. No breakout, killed like 6 mosfets so far, it's just brutal.
So, I thought why not use an active gate drive ZVS, basically what neon-john did with his mains powered ZVS induction heater.
Use a pair of schmitt trigger NAND gates, with UCC drivers on the gates, it would be practically bulletproof, and since it's active gate drive, there wouldn't be an issue of latchup with the gates. (only one can be on at a time, due to the NAND gates) Problem I see; Getting the gate drivers to work with 2.56 mhz... maybe a bipolar totem pole?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Bleh, you should probably do your homework by telling us all about what you did with your coil.
Which NAND gates did you use? Steve Ward had 74HC14 in his original circuit, and considering how finicky it is I wouldn't be surprised if other IC's be it other gates or just different versions (LS, AC) didn't work at all.
I told you to remove the weird topload thing with a 5mm thick screwdriver or whatever protruding from it (which would likely need like half a kW to even break out) but you seemed to ignore me. And I don't even know if you know you need to swap your primary leads in case of oscillation failing!
The sad truth is, Steve Ward's feedback circuits suck (well, most of them, apart from his new predikter driver and some old SSTC circuits), and making variations of them might end up sucking even worse, to the point where it just keeps blowing up.
But since his mini SSTC apparently worked so well I guess it wouldn't hurt you to just blatantly copy everything in it and hope for the best (yes, that includes replicating his primary and secondary configuration too)
Don't bother with any bizzare hoemade gate driver topologies as they'll just cause unnecessary frustration. UCC's should actually work to some point at 2Mhz but will run very hot, and I'd suggest to just get rid of your mini secondary and make a beefier one.
The only two remaining recommendations from me - if you intend to punish your mosfets hard, make sure to have them properly mounted onto individual heatsinks without mica insulators and positive pressure over the die.
Second, do install some kind of overcurrent protection circuit - a small CT, LM311 and a NE555 monostable to disable your UCC's in overcurrent condition would be ideal. I'm quite sure this would save you lots of mosfet lives if you did it right.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Dr. Pork wrote ...
Bleh, you should probably do your homework by telling us all about what you did with your coil.
Which NAND gates did you use? Steve Ward had 74HC14 in his original circuit, and considering how finicky it is I wouldn't be surprised if other IC's be it other gates or just different versions (LS, AC) didn't work at all.
I told you to remove the weird topload thing with a 5mm thick screwdriver or whatever protruding from it (which would likely need like half a kW to even break out) but you seemed to ignore me. And I don't even know if you know you need to swap your primary leads in case of oscillation failing!
The sad truth is, Steve Ward's feedback circuits suck (well, most of them, apart from his new predikter driver and some old SSTC circuits), and making variations of them might end up sucking even worse, to the point where it just keeps blowing up.
But since his mini SSTC apparently worked so well I guess it wouldn't hurt you to just blatantly copy everything in it and hope for the best (yes, that includes replicating his primary and secondary configuration too)
Don't bother with any bizzare hoemade gate driver topologies as they'll just cause unnecessary frustration. UCC's should actually work to some point at 2Mhz but will run very hot, and I'd suggest to just get rid of your mini secondary and make a beefier one.
The only two remaining recommendations from me - if you intend to punish your mosfets hard, make sure to have them properly mounted onto individual heatsinks without mica insulators and positive pressure over the die.
Second, do install some kind of overcurrent protection circuit - a small CT, LM311 and a NE555 monostable to disable your UCC's in overcurrent condition would be ideal. I'm quite sure this would save you lots of mosfet lives if you did it right.
Marko
I apologize Marko. I did everything you suggested to do. I took off the topload, and left just the nail. I swapped primaries.
I got it to oscillate, (still no breakout, just tiny tiny little sparks. Enough to light up fluorescent tubes and neon lamps but nothing else. Swapping the primary around made the sparks disappear completely. ) but once I added 50 volts to the power, the mosfets decided to die. So, then I tried to recreate a class E tesla coil; That failed miserably as well, as I could not get the coil tuned into class E operation.
I'm going to just put the little secondary away, (maybe try the active gate drive thing with the ZVS, MAYBE...) and build a proper one. I'm tired of dead mosfets.
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Active Gate Drive ZVS for HFSSTC
