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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I whipped up an off-line flyback driver from spares I have left over from the smps, but I haven't plugged it in yet. What bothers me is current limiting, as you can see by the circuit I have none. Will this be a problem? Or will the core size, primary resistance, reactance, something limit current automatically? I just don't want a catastrophic failure from my first arc... So will it limit itself, or will I need a series light bulb in the circuit forever? (I'll use one the first run of course. )
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
You could use a SG3525 and drive the GDT directly, or maybe wire TL494's outputs into a push-pull and use a 1:2:2 GDT.
Depending on the frequency you want to run, you can safely use a much smaller nubmer of turns on GDT.
For some 40KHz you'l probably be good with twice as less, and rather make care that your GDT is well insulated and that wires are fat. Use cat5 or shielded cable and wrap it around the core, then use all white wires (or braid) as primary and paralell others for secondary.
You shouldn't go much over 40kHz with mosfet's body diodes, since their slow recovey.
Not much else to say I guess, just set your duty cycle low at beggining, ensure gate drive works and increase it slowly.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
you should put some inductor in series with the mains, if you dont want a big bang every time you switch it on (maybe the diodes in the bridge can also fail because of this current pulse) edit> discharge resistors on the filter caps are also a good idea.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
With 80 primary turns it should be OK i think, but you may require more (like 100 or more). I ran a flyback driver from mains (120VAC) and i recall using around 50 primary turns for good results. Just uhhhh.... put a fuse on the mains, ok? 2A should be *plenty*. Even 1A will be enough for a flyback.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Steve Ward wrote ...
With 80 primary turns it should be OK i think, but you may require more (like 100 or more). I ran a flyback driver from mains (120VAC) and i recall using around 50 primary turns for good results. Just uhhhh.... put a fuse on the mains, ok? 2A should be *plenty*. Even 1A will be enough for a flyback.
I am not sure if the fuse won't blow when the caps are being charged, use a slow-blow type. As for the number of turns, I used 60 turns for halfbridge on 230V, but that was with "brute force" driving. You could maybe use waay more turns (200? 300?) when you tune your frequency to the flyback's resonant one, because on my flyback when operating "in tune" it gives ~5-10x the output voltage of that when not in tune.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I just blew my last half-bridge. The one I was going to use had been destroyed earlier, so I used my smps to drive the flyback. Original primary, no current limiting. All I got was puny arcs though, smaller than my ZVS! Then I foolishly turned it on while it could arc and I blew my last two IRFP450s... Afterwards I realized I was running the flyback at 5% duty cycle , so when I put some new mosfets in place I'll try full power!
I've got 20 200v 14 amp mosfets, will these work? If not can I series 2 of them for 400 volts?
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