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Methods to Test a ZVS Driver

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quicksilver

Sat Jan 15 2011, 04:22PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I had been thinking about this for some time.
Is there a method to use a DIMM to test a Mazelli driver without connection to a flyback? Many DIMM's have a frequency testing element: could that be implemented? The cost of those MOSFETs are high enough so that I wouldn't want to blow them if possible.
I was trying to make a driver that was tight and cute in the manner of many here who have that skill but I wanted to make sure that my wiring as correct prior to hooking it up in case of a mistake.
Is there a method of testing without risk to the the FETs?

Proud Mary

Sat Jan 15 2011, 04:49PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The circuit depends on energy stored in the primary inductance to keep itself going into the next cycle.

The primary inductance is also one of the frequency determining elements.

You could run it at reduced power to test it, of course.

quicksilver

Sat Jan 15 2011, 06:22PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I had the mistaken notion that similar to other drivers I was altering frequency via the design of the driver BEFORE it entered the LOPT.

Therefore (if I understand this correctly) my primary on the LOPT becomes much more significant (number of turns beside the center tap) Thus the LOPT & ZVS work as a unit. I had not understood that, I erroneously believed that the inductance of the toroid choke (or what have you) contributed to frequency alterations prior to the LOPT; contributing to frequency alterations in a "filter" type concept.

Adam Munich

Sat Jan 15 2011, 08:51PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

You could just take the flyback off the core and use that to test it. That's what I do.

Proud Mary

Sat Jan 15 2011, 10:00PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

quicksilver wrote ...

I had the mistaken notion that similar to other drivers I was altering frequency via the design of the driver BEFORE it entered the LOPT.

Therefore (if I understand this correctly) my primary on the LOPT becomes much more significant (number of turns beside the center tap) Thus the LOPT & ZVS work as a unit. I had not understood that, I erroneously believed that the inductance of the toroid choke (or what have you) contributed to frequency alterations prior to the LOPT; contributing to frequency alterations in a "filter" type concept.

Ideally, a choke should play no part at all in frequency determination. Where chokes do ring or resonate at some frequency within their range, this should be considered a fault in need of a remedy.

In the "Mazzilli" type of push-pull oscillator, the principal frequency determining elements are the centre-tapped primary winding, and the capacitor across it, which together constitute a tuned circuit.

quicksilver

Sun Jan 16 2011, 11:39PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I have not had time to experiment with this, but do you think that the tuning of a Mazzilli oscillator circuit needs to be "tight" in-so-far as the "tuning" or is there more room for flexibility in terms of number of turns of the primary or capacitance for instance?

Thank you, by the way for illustrating that for me.

I ask this because unlike simplistic single transistor driver circuits, the Mazzilli (superficially) appears to be either working well or not functional when I have made one previously.

QUOTE:
"You could just take the flyback off the core and use that to test it. That's what I do."

I only have AC's that I could do that with.....is that what you used (an AC LOPT)?
I'd have a damn hard time pulling apart a DC flyback.

Proud Mary

Mon Jan 17 2011, 12:24AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

quicksilver wrote ...

I have not had time to experiment with this, but do you think that the tuning of a Mazzilli oscillator circuit needs to be "tight" in-so-far as the "tuning" or is there more room for flexibility in terms of number of turns of the primary or capacitance for instance?

I'm sure there will be quite a range of combinations of L and C which will meet the conditions necessary to sustain oscillation in this circuit.

The Q - or "goodness" - of the primary inductance will depend on the composition of the core material, which may have been optimised to work at - for example only - TV line frequencies around 15.625 - 15.750kHz.

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