Flyback

I have one, and I want to power it up. How can I do that? Could I just hook up mains to the computer board that it's sitting on and have hv? Or how can I do that? Also how do you drive stepper motors? I have some that have a pcb with 4 things.

` said:

I have one, and I want to power it up. How can I do that? Could I just hook up mains to the computer board that it's sitting on and have hv? Or how can I do that? Also how do you drive stepper motors? I have some that have a pcb with 4 things.

Click to expand...

You need to build a driver for the flyback. This is a simple guide to making a flyback driver.
http://www.powerlabs.org/flybackdriver.htm

Whatever you do, NEVER hook mains straight to the flyback, unless you want pieces of ferrite throughout your body. Hook that thing up to mains and the core becomes a bullet.

Ive used the single transistor driver without problems, and its damn easy to make.

This is my favorite flyback driver:



circuit description:

The most crucial part of the circuit are the MKP capacitor and the flyback primary winding. Keep really shorts the connections between the resonant circuit (capacitor - flyback) and the mosfets. The primary is hand wound on the flyback, 4+4 turns of heavy wire, can be done with some bifilar to make things simpler. Use a STRONG capacitor, at least rated AC 5x your supply voltage, possibly an high current mkp one.
It's rather easy to build, you can choose to put it together on a small heatsink if you're planning to get high power off it or you are using high loss fets, or it can be made "on the fly", since each fet will dissipate only while feeding the zvs circuit, so RDSon * (Isupply/2)^2 * 0.5. normally its a small power, average less than a couple of watts per fet.
Pulloff diodes are soldered directly between the gate and the opposite drain of the mosfets.
The inductor is not crucial, you can also use an old inductor off a pc psu filtering, using the thickest wires ther (normally 5V ones). chose something between 50 and 300µH.

Output frequency is chosen by the flyback's primary and the cap, as usual F= 1 / ( 2pi * sqrt ( L C ) ).

some pics of the driver:




power output can be pushed from some ten's of watts to many hundreds... I've ran some flybacks over the 500W level with this circuit, pretty incredible driver

You can use the ballast circuit from a CFL ( compact fluorescent lamp ) as a driver for flybacks, as far as I'm aware anyway.

-Adam

Diachi said:

You can use the ballast circuit from a CFL ( compact fluorescent lamp ) as a driver for flybacks, as far as I'm aware anyway.

-Adam

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I have a bunch of useless ballasts lying around. Post a schematic showing how to do this and I'll try it.

Coherent said:

[quote author=Diachi link=1231719166/0#4 date=1231784831]You can use the ballast circuit from a CFL  ( compact fluorescent lamp ) as a driver for flybacks, as far as I'm aware anyway.

-Adam

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I have a bunch of useless ballasts lying around.  Post a schematic showing how to do this and I'll try it.[/quote]


the ballast will have two wires going in ( AC input ) and 4 wires going out ( your filament wires for the CFL ) the two outer wires out of the 4 are your HV out , i think it's 1000V at 400Hz ( could be a higher frequency ). You simply connect your filament leads to the primary of your flyback. Connect the two out wires from the ballast onto your CFL ( the inner two are your neutral ).

That should do the trick anyway. Some CFL ballasts need to "sense" the presence of a filament, to sort this you just put a cap on a pair of the positive and neutral wires. a 1000V ceramic cap should probably work just fine