Steve McConner wrote ...

No, you can buy a crystal oscillator for a few bucks with a square wave output. People use the 4MHz ones to drive Class-E SSTCs.

The real reasons why nobody uses crystals are:

The resonant frequencies of flybacks are low, <100kHz, and you don't get a particularly good choice of crystals down there. 32.768kHz is the only off-the-shelf value I can think of.

The frequency doesn't need to be that stable. A good RC oscillator, like the one in a TL494 or 555, is fine.

The easiest way to find the resonance is to connect up the flyback to your power oscillator and tune for maximum smoke. To do this the oscillator has to be adjustable, which RC ones are, and crystals aren't.

The RC is cheaper.

So it wins on three counts.

Getting back to the original topic, RTFArchives, you will find plans for Kim Ladha's self-oscillating induction heater, a simple circuit successfully copied by many people here. I think the thread title was "OMG Induction Heater" or the like. I prefer a circuit using the 4046.

Steve McConner wrote ...

Well that's why I told you to go search for that Kim Ladha's circuit which doesn't contain a 4046.

You'll need to order some gate driver chips anyway.

I don't know where you got the idea that you needed a transformer to use a ZVS. I built a goofy one with a ferrite-cored matching transformer, but I've seen any number of ZVS induction heaters, where the maker just put a center tap on the work coil, or used a bifilar work coil, or used two DC link chokes, one to each end of the work coil.

Or did you mean a 60Hz transformer, the implication being that you can only use the mains, not any lower voltage, because you don't have any kind of low voltage power supply? In which case too bad, better get one, the mains is not a good or safe place to start. It's kind of like saying that you'll trim your hedge with machine gun fire because you don't have a ladder.

Steve McConner wrote ...

Well, if you can make a good resonant circuit for induction heating, that is to say a coil of good thick wire and a beefy capacitor that can handle lots of current, then you can just sling it between the two MOSFET drains and use it as the resonant part of the ZVS. You don't need those two inductors or anything. The only hard bit is getting a center tap on the work coil to feed the DC power in, but I discussed solutions for that in my previous post.

It probably won't handle a 160V supply. I struggled to get mine above about 50V before it died of parasitic oscillations. You're probably best to run it off some big iron cored transformer.

James wrote ...

No, it doesn't have to be that exact chip, there are piles of different ones that would work. Nand and inverters are both good options. You do want the Schmitt trigger type if you can find them though. These snap on and off nice and cleanly and are less likely to float in undefined states. Either way you can get a few of them for free

The main reason crystal oscillators are not used for this sort of thing is that the resonant frequency of the transformer changes with... pretty much everything. Voltage, primary windings, load on the output, etc. Also you don't need anywhere near the precision, a simple RC oscillator would work just as well but the whole point of a resonant oscillator is that it's self tuning.

I know you're avoiding transformers, but I really do recommend you give it a try. As a member of 4HV you must have a melted down flyback or two by now? Just pull the core from one. Transformer coupled makes it SO much more versatile and effective. Took me less than 5 minutes to wind my transformer and didn't cost a dime.

I would also again encourage you to build a stock unmodified mazzilli driver first. It's flat out the easiest cheapest most bare bones driver of that nature I've found. Mine will make some arcs from a flyback down to 5V input, albeit weak ones.

Inducktion wrote ...


I've actually already made the ZVS basic driver quite a few months ago. It worked great. Nice fat arcs, and the circuit itself was pretty neat, and tidy.

I tried making an induction heater with it just with a plain center tapped work coil, and im almost positive that's what killed it.

And as for the Royer improved circuit from neon-john, I've got pretty much everything i need, or going to get the things I need tomorrow. I'll try building it and stuff sometime this week, and hopefully i'll get it working well. And the one thing I'm worried about with the flyback core, is it will saturate at the higher frequencies...and will overheat, or so I understand. I'll try and figure out how many turns and all that good stuff.

James wrote ...



Try the transformer with the Mazzilli driver first. If it cooks that, it WILL cook the mains powered driver. Higher frequency ought to reduce the likelihood of core saturation, but the losses in the core do increase and cause it to run hotter. What worked for me is mazzilli circuit fed with 50VDC driving a flyback core with 5+5 turns primary. Secondary is 2 turns of #4 car stereo power wire connected to a ~1" diameter coil of 8 turns of #12 bare copper wire.

Take your time and get it right or you'll spend a lot more converting expensive IGBTs into landfill material very efficiently.