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How to troubleshoot the mazzilli flyback driver?

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cavemen

Sat Mar 14 2009, 03:10PM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

I built this project and ran it from a PC power supply.

I got a 5mm spark from the flyback, I could "hear" it work at about 2000hz with my brain and my ears.
Only a half of it got warm and worked, though. I could feel one MOSFET get warm and the other one stayed cold.
I also limited current with my special 0.3 ohm resistor for safety.

So i tried to find a problem and it was one of the zenders. This zender was not soldered in with both ends. I fixed the problem and something unexplainable started to happen.
There was no need to limit the current.

It does not work. Nothing gets warm, yet all voltages are in the right places on the circuit.
It seems like all components work properly. Flyback's secondary works according to some test that I also use to find the ground pin.
How do I get it to work? I spent a lot of money and time on this device.

Dr. Dark Current

Sat Mar 14 2009, 03:38PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Not enough info

Have you checked all the components, mainly transistors and the fast feedback diodes?

Are the diodes "crossed", ie. that one goes from FET1's gate to FET2's drain and vice versa?

Do you have a 5+5 turn primary with both halves the same direction?

Have you properly identified the HV return/ground pin on your TV transformer?

Probably not the cause, but is your resonant capacitor of good quality (polypropylene/MKP)?

Littlew

Sat Mar 14 2009, 07:09PM

Registered Member #1448 Joined: Sat Apr 19 2008, 01:16PM
Location: Russia/Moscow
Posts: 21

change your resonaunt capacitor to polypropylene capacitor
also use stick to draw arcs, ZVS output can kill you or damage your hand(even burn hole to bone)

cavemen

Sun Mar 15 2009, 03:40AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Checked everything.

Does this thing even work?

In my case, the drains of the MOSFETs are crossed. Same things are interconnected as in the plan.
6 loops on each half of the ferrite core.

I had never seen a homegrown device that works.

Why both of my 400v diodes measure 0.450 megaohms in BOTH directions (in a circuit)
and such diode measures 5.2 megaohms in one directions and (ofcorse) infinite resistance
in the other, while out of this circuit.

Is this normal?
I have all sorts of diodes from rectifiers.
R those fast enough?

I will show more pics when my camera would be ready.

MRacerxdl

Sun Mar 15 2009, 03:49AM

Registered Member #989 Joined: Sat Sept 08 2007, 02:15AM
Location: SÃ£o Paulo, Brazil
Posts: 476

Measure the diodes with the conduction mode of the multimeter (usually they have a diode icon on it) you should get a value when on one side, and nothing in the other side.
What is the code of the Diodes?

cavemen

Sun Mar 15 2009, 04:03AM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

I canno read the code, because it is smeared on all of them, beyond recognition.
Diodes work like normal diodes. I tested it with a battery and a light bulb. My fears that i bought something wrong are gone.

All parts of te circuit are energized.

Dr. Dark Current

Sun Mar 15 2009, 08:23AM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

If the diodes are from line frequency rectifiers, they will most likely NOT work in this circuit. You need the ultrafast type, such as UF4007.

cavemen

Sun Mar 15 2009, 02:55PM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

Yes, I got rectifier diodes. "Fast" or "slow" is not something that can be turned into numbers.

If diodes would have had conducted both ways at high frequency, there would be current consumption, heat and signs of inefficient work.

This is where i bought the zenders.

I cannot find the reference to the capacitor anywhere.

cavemen

Sun Mar 15 2009, 03:02PM

Registered Member #2008 Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118

how i restructured the circuit

Dr. Dark Current

Sun Mar 15 2009, 03:04PM

Registered Member #152 Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384

Ha! Those diodes are slow, Get UF4007 or BA159.

But mainly, you are supposed to use 12V or 15V zeners, not 2.4V! It is no surprise that it does not work, as 2.4V is not even enough to cause any current to flow through the FET.

If you are using just 12V, then you should be OK with removing the zeners completely. But first replace the diodes.

""Fast" or "slow" is not something that can be turned into numbers."
Of course it can, it is called reverse recovery time and measured in microseconds or nanoseconds. A good diode for this circuit should have sub-200ns reverse recovery time.

P.S. Its not zender but zener, just so you know

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