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Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Hi I’m new here and I built a ZVS flyback transformer driver. I was wondering if there is anything I can do to make it better besides getting better MOSFETs.
Registered Member #51
Joined: Thu Feb 09 2006, 04:17AM
Location:
Posts: 263
IRF740 MOSFET's are 400v, .55ohm devices. If you use something with a higher voltage rating, like 600v, you can use a higher input voltage. Using a device with a lower on resistance will lower the amount of power lost in the MOSFET's, and allow you to push more current before the transistors overheat. Also, use a cap that's bigger than .33uf. Try something like 1uf. How many volts are you currently putting into your driver? What kind of output length are you getting? A pic of your entire setup, including flyback, and primary would be useful. If you have any more questions, just ask, I'd be happy to help.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Make your leads short and thick- especially those from fets to the resonant cap and from the cap to the primary. Use a thick wire for the primary to avoid overheating. Use a high quality resonant capacitor (PP type or "X2" type found in power supplies works very well). For higher power use better fets, such as the IRFP250. Hope this helps
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Oh by the way I get 6 cm arcs at 24V, is this good?
6 cm is pretty good for the voltage. You can generally increase output power at lower voltages by decreasing number of primary turns and increasing the tank capacitor.
ALso, your mosfets are a bit of too high voltage rating and too high Rds ON. Some 100-200 FET's are most used, IRFP250 is one of favorites. IGBT's also work well.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Too bad my flyback died by arcing from one pin to the other with no output at all. But what's strange is it only arcs from pin to pin when the HV output is shorted to the ground.
What should I do with the other outputs on the working flybacks?
About what AWG should I use from the fets to the caps?
When I was building it I tried to keep the tips from here in mind.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
If you get arcing on the flyback's base, check for all "groups of pins" (pins that are electrically connected together), and then ground each "group" once. (it doesn't matter which pin in each "group" do you ground)
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Myke wrote ...
Is it ok that it hapens at 12V because I think it should only do it at 24V or higher? Is the flyback dead because it didn't use to do that before?
If it didn't do that before, and you have no output at all (as you said previously), then yes, it's probably dead (probably from internal insulation breakdown)
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ZVS Qs
But what's strange is it only arcs from pin to pin when the HV output is shorted to the ground. 
