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Tweaiking a flyback driver

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LAN_403

hvduffer

Sat Apr 18 2015, 02:08PM

Registered Member #54487 Joined: Mon Feb 16 2015, 02:29PM
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Posts: 8

I put together this basic flyback driver driver replacing the 10000mfd cap, the transformer and rectifier with the 12 volt output of an ATX power supply rated at 12 Volts 20 Amps. It works very nice, draws an arc at about 15 mm and can be drawn out to about 20 mm. The transistors are mounted on separate heat sinks. The transistors and heat sinks get lukewarm after about 30 seconds.

I have not been able to include the schematic ( ??? ) so here's the url of the web page where I got the circuit.

Considering the simplicity of the circuit, I would like to tweak it to produce larger arcs, before stepping up to the next level circuitry.

I would appreciate any suggestions.

Thanks

Ash Small

Sat Apr 18 2015, 09:09PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I've sent you a link which you can use to paste the circuit into your post above.

You could try adding/removing turns on the primary and feedback windings, one at a time, to see if there is any improvement, or otherwise (I wouldn't advise reducing the number of turns on the feedback winding initially).

The smaller the core, the more windings it needs. it's a 'volts per turn' thing, a bigger core can take more volts per turn.

I'm not familiar with this circuit muself but it looks like a 'push-pull circuit. These don't tend to work to well with DC flybacks (The web page you linked to does specify an older, non-rectified flyback), generally push-pull circuits don't need a 'gapped core', although a gapped core still works in some cases, eg with the 'Mazzili' driver circuit, so it MAY be worth experimenting with the gap size, or no gap at all, if you are able to take the cores out and remove the plastic spacer in the gap.

Without more information, eg regarding the type of flyback you are using (a photo would help here), there isn't a lot more that we can advise.

I think all the above is correct, as I said, I've not used this circuit myself.

EDIT: you may want to limit the current to the circuit while testing. A 12 volt automotive lightbulb can be used for this, in series with the power supply. You can use Ohm's law to work out the current from any specified wattage bulb.

You may also want to use old computer fans to cool the heatsinks (these can be powered from the 12V ATX supply), and you may also want to try looking for some bigger heatsinks. Again, a photo of your existing setup would be useful to us here.

dexter

Sat Apr 18 2015, 09:43PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
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Posts: 195

i'd say go higher in volts for the power supply
or go to the next step: a ZVS

Ash Small

Sun Apr 19 2015, 12:53AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

dexter wrote ...

i'd say go higher in volts for the power supply
or go to the next step: a ZVS

As I understand it, there is no point going with a ZVS (eg Mazilli) driver if using a DC flyback.

We need some photo's, or, at least, some more information.

Dragon64

Sun Apr 19 2015, 04:20AM

Registered Member #1438 Joined: Sat Apr 12 2008, 12:57AM
Location: Canada
Posts: 218

You could try driving your flyback with a 555 and a MOSFET.

dexter

Sun Apr 19 2015, 10:24AM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
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Posts: 195

Ash Small wrote ...

As I understand it, there is no point going with a ZVS (eg Mazilli) driver if using a DC flyback.

We need some photo's, or, at least, some more information.

so what if one half of the sinewave is blocked by the diode?
phasing is a non issue
the fact that the Mazilli driver works at resonance means the primary coil see about 3.14 times the supply voltage giving it a much higher volt per turn - that's the reason it requires gapped cores

4+4 turns 12V from a 12V 4.5Ah lead-acid the arc starts at 6mm and can be extended op to 60mm

i also ran the same setup from 36V but 5+5 turns with impressive results, arc starts at 30mm and extended up to 60mm

Ash Small

Sun Apr 19 2015, 10:31AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thanks for clarifying that Dexter. I stand corrected.

As I said, I'm not that familiar with push-pull circuits. My main interest is in flyback topology.

Nice video

EDIT: Frequency also plays a part in the 'volts per turn' thing, Higher frequencies mean higher volts per turn. It's a 'volt seconds' thing.

dexter

Sun Apr 19 2015, 12:04PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

Ash Small wrote ...

EDIT: Frequency also plays a part in the 'volts per turn' thing, Higher frequencies mean higher volts per turn. It's a 'volt seconds' thing.

in the case of a Mazilli driver lowering the numbers of primary turns increases the volt/turn ratio for both reasons: 1. fewer turns for the same voltage and 2. higher frequency due to lower inductance in the resonant LC

hvduffer

Sun Apr 19 2015, 04:11PM

Registered Member #54487 Joined: Mon Feb 16 2015, 02:29PM
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The flyback I am using is a "modern type". It is out of 5 to 10 year old JVC television set. HV cable comes off the top and has two small adjustable knobs, FOCUS and SCREEN. There is a part number but no manufacturer's name .

I have a couple of other flybacks more or less the same, with small differences in size and/or geometry.

Nothing on Google under the part number.

Ash Small

Mon Apr 20 2015, 03:26PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

This link may be useful in identifying your JVC flyback:

It lists HR Diemen equivalents, and often gives quite a lot of information, including internal schematics, etc, but not in every case.

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