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My experiences with the Mazilli driver

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LAN_403

Platinum

Fri Sept 06 2013, 09:46PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I thought I'd share some of my experiences with this driver.

I have used this driver before, but that was a few years ago, when I was pretty dumb. A few things I've noticed are:

This driver will go into parasitic oscillation if you do not keep it's frequency low (8-50~Khz). (With my FET/IGBT's anyway, 40n10, 25n120)

If the driver does go into bad oscillations it will give an awful output and the arc will screech although the frequency of the circuit is above hearing ranges. Yet I have found that if this does happen, the driver will operate without a inductor and give better results, but in the first place these oscillations are unwanted. This produced alot of heat.

Also if you close the airgap of a flyback's core frequency drops alot, and if you increase the airgap frequency rises, I have measured 388Khz with 2.5mm air gap, 4+4 turns and 0.8uf tank cap.

The circuit can operate with only these components:

MOSFET's

Ultrafast diodes

470Ohm resistors

Inductor

Capacitor bank

I built 3 of these drivers today, and they all work very well after some troubleshooting and I did not use 10k resistors and zener diodes.

This circuit doesn't really like IGBT's, and I used 25n120, 30n60. And yet a 40n10 is best.

Pictures included.

Thanks! :)

Inducktion

Sat Sept 07 2013, 07:05PM

Registered Member #3637 Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068

You're destroying the mosfet/IGBT gates by not using zener diodes... They're kind of needed, though the circuit WILL work, you're killing your semiconductors needlessly.

The inductor is also a pretty decent must, as it acts as a current limiter/current source for the output.

What kind of power supply are you using?

Platinum

Sat Sept 07 2013, 11:56PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I'm using 16vdc for gates, and 48vdc for power.

I found these circuits work well for driving flybacks, but thing is, I'm not even using zeners, gate resistors, yes it's kind of obvious that inductors are needed in this circuit.

I was just showing what I have learned.

TwirlyWhirly555

Sun Sept 08 2013, 11:20AM

Registered Member #4104 Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122

Ive never used Zeners of my Mazilli driver , I always use a separate 12 Volt gate drive and just been lucky I guess , plus I use 280 Ohm gate resistors with 12V supply . and I tune my ZVS drivers to run at around 25 KHz with a arc drawn .

Looking at the single on a O scope the gate voltage peeks at 16 Volts on my current setup ,

Steve Conner

Sun Sept 08 2013, 06:16PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The circuit will work without the inductor if you have a transformer with a saturable core. It gives a square wave output with a frequency determined by core saturation. You should really remove the resonant capacitor too.

If you hook it up to an ordinary iron-cored transformer and connect it to a 12v supply, you get a very simple inverter that can drive many small appliances.

I'd argue that it isn't really a Mazzilli driver any more, since this ferroresonant version was known as a Royer or Jensen oscillator and used (with BJTs) right from the dawn of the transistor age. Vladi Mazzilli introduced the diode gate drive arrangement to allow the circuit to be built with MOSFETs, and added a DC link inductor and resonant tank circuit.

He originally built it with an air cored coil driving a Tesla resonator, so he needed something that would oscillate even without the saturable core. He still called it a "Royer" but the people of 4hv thought it was different enough to deserve a new name.

Platinum

Sun Sept 08 2013, 09:36PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

So as you said, if you remove the inductor and capacitor, the circuit will run any type of transformer, iron/powder, ferrite, if it can saturate? If I understand correctly. Will this destroy the circuit when used for driving flyback's?

Will this circuit run more efficient with BJT's?

Steve Conner

Sun Sept 08 2013, 10:04PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

A flyback transformer normally has an air gap, so it may not saturate sharply enough to work well in the ferroresonant version of the circuit. It may well be destroyed but it seems to me that the Mazzilli version gets destroyed quite often driving flybacks too.

The same applies for iron powder cores, these have a distributed air gap that gives them a very soft saturation characteristic.

The circuit is actually a poor match for BJTs because it supplies the maximum base current all the time. If you must use BJTs, the series resonant circuit used in electronic halogen and fluorescent ballasts is better, it only supplies as much base drive as the transistors need to pass the load current, so they switch more efficiently (but probably still not as good as a MOSFET or IGBT- BJTs are used in these ballasts because they're cheap)

Platinum

Sun Sept 08 2013, 11:07PM

Registered Member #3926 Joined: Fri Jun 03 2011, 08:32PM
Location: UK.
Posts: 525

I just tried this Mazzilli oscillator without a capacitor bank and inductor with a flyback transformer with a removed airgap, and the circuit pulls alot of amperage (my ammeter can only measure up to 25Amps) output current is very low on the flyback side, so low it's a snaking arc, thin strands of plasma.

I also ran the circuit without a capacitor bank, but with an inductor and I had more output voltage than the original circuit but at the cost of current.

EDIT:

I would now like to run this oscillator on 70~Vdc, what components will I have to change? And what MOSFET's are suitable? Because I would like to order parts.

Thanks.

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