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Just thought I'd share a very simple project I made recently when taking a break from building Tesla Coils. I wanted a very simple, reliable and no-frills general-purpose Flyback driver. Specifically I bought one of Fiddy's Flyback Transformers (http://4hv.org/e107_plugins/forum/forum_viewtopic.php?165666) some 2 years ago on this forum and have been feeling a little sad that I haven't actually driven it yet!
I decided to go for a simple half-bridge topology (i.e. so I won't be driving the flyback in 'flyback' mode). Drive logic is provided by the venerable single 555 timer IC, with adjustable frequency operation from 30kHz to 80kHz or so. I designed this circuit to be extremely simple so anyone can build their own too!
Next I also wanted to make the driver as robust as possible so I added an over-current protection scheme, which is very simple. Peak current was set conservatively at 7.2A (for now) and feedback taken via a simple CT.
I've used some nice IXYS FETs good for 250V 80A, but they're currently running at just 36V. Finally I made a PCB for it and put everything (including a 36VDC power supply) into a spare computer ATX power supply for simple plug-and-play operation.
It works! Here's it driving Fiddy's flyback and powering a miniature Jacob's Ladder. The driver work great for all other flyback transformers as well.
I suppose it's time to increase the power. Thanks for reading!
Registered Member #58522
Joined: Tue Mar 15 2016, 08:33PM
Location:
Posts: 50
Hello loneoceans, I have read your web page with great interest! Good work getting the half-bridge to work. I think half bridges are cool too. I wrote a guide myself on building half-bridges with circuits included:
And a spreadsheet to design them
If you build it, I highly recommend building the version that uses the gate drive transformer, it is much more forgiving.
I have used my half-bridge to drive a Tesla coil, but I have had a hard time keeping the transformer from getting fried. My transformer generates about 30 kV on the secondary and I think the spikes generated by the Tesla coil in the spark gap are very hard to filter with such a high voltage. I can draw some sizable arcs with it though.
I recommend buying these if you want to try to wind your own transformer if you order from the USA:
The Kaschke U/I set can be used in pairs so you can get a truly monster ferrite core, one that you can wind 500 turns on, which I have done, to get 30 kV running off of 120 VAC mains power.
Also, I am trying to build a dual MOT tesla coil based on your Tesla Coil 2, but using the Villard multiplier and not 4 MOTs. I noticed you had problems keeping the diodes from being fried.
I am trying something a little different. I am using 4 microwave oven diodes in series rather than 2 so that the reverse bias voltage is higher. Also, like a Terry filter, I am using 10 1800V MOVs to absorb any transients from the Tesla coil to try to protect the diodes. I also have a 1000 pF/36 kV capacitor filter with 600 ohms in series with it on each leg of the power supply.
I don't know what you have tried since you updated your page but if you could share any info that would be helpful! I am working on building my rotary gap right now using an angle grinder.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
Nice! If you're not driving it in flyback mode, is there any benefit to removing the gap in the flyback transformer or doesn't the extra leakage inductance matter in this case?
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Half-Bridge Flyback Driver with Over Current Protection
