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ZVS flyback troubles

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Mads Barnkob

Fri Jul 18 2008, 04:49PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Hi

I have build the mazzilli driver and it seems to work, I can get about 40-50kV at as low voltage as 8 Vdc, and it will grow thicker and hotter towards the 40Vdc, it will arc to the ferrit core of the flyback until about 25-30Vdc.

It was when I hooked up the gates to my scope it seemed strange, the gate signals are identical where I was thinking they would be running in each their half period. I have checked the circuit many times and cant find any construction faults.

Attached are pictures of the driver, all components are the ones descriped in the orignal schematics or similar, all checked.

The scope picture is showing both channels, and its set to trigger on channel A, but no matter the trigger settings they are always identical.

Dr. Dark Current

Fri Jul 18 2008, 05:10PM

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

well, if the circuit works as it should then theres probably a problem with your scope setting/bad connection of probes etc. If the signals were identical there would be no voltage on the primary.

GeordieBoy

Fri Jul 18 2008, 05:31PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Try flicking the Vertical Mode switch from "Dual" to "Chop" and make sure the Trigger Source is selected as Channel A only. Also make sure both scope probe's ground leads are connected to the DC bus negative rail.

Mads Barnkob

Fri Jul 18 2008, 05:55PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Seems to be troubles with the triggering, if I adjust it for channel A, channel B wont show and vice versa.

There is a switcher for Normal sync and TV sync. each with a positive and negative setting, flickering it between positive and negative seems to show the picture I would like to see, so the problem is unfortunately my old scope :(

never had luck finding a manual for it and very little experience in using one.

both ground leads are connected to negative rail

Mads Barnkob

Fri Jul 18 2008, 05:57PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Forgot to attach picture of the other half of the scope.

Antonio

Fri Jul 18 2008, 09:38PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

Did someone ever manage to run a reasonably correct simulation of the Mazzilli driver? A simulation with linear inductances in SwitcherCad III doesn't work well. Maybe it requires core saturation, in the flyback or in the series inductor.
The operation appears to be very sensitive to the series resistance of the power supply.

Myke

Fri Jul 18 2008, 10:55PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Set triggering to NORM and set the input to CH A?

Mads Barnkob

Sat Jul 19 2008, 05:23AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Antonio wrote ...

Did someone ever manage to run a reasonably correct simulation of the Mazzilli driver? A simulation with linear inductances in SwitcherCad III doesn't work well. Maybe it requires core saturation, in the flyback or in the series inductor.
The operation appears to be very sensitive to the series resistance of the power supply.

I am using a rewound MOT as the supply, full bridge rectified without a smoothening cap, I did not have any that would not heat up too fast.

Myke wrote ...

Set triggering to NORM and set the input to CH A?

I have tried all the combinations without any different result than the 2 signals being identical

Mads Barnkob

Sat Jul 19 2008, 05:53AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

Here is a measurement of the AC supply, full wave rectified DC and the two signals together. There is no difference between using dual or chop. Trigger settings where Normal + and channel A.

Seems there is too much internal noise between the channels and it impossible to use both channels at the same time for a reliable result :(

Antonio

Sat Jul 19 2008, 12:55PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

How did you connect both probes to measure the AC input and the full-wave rectified output? If you are using a diode bridge (4 diodes), this is not possible, as the ground is not the same.
A capacitor that heats up quickly? Very strange, as capacitors normally don't dissipate significant energy. Possibly a wrong connection or insufficient voltage rating.
Are the red buttons in the "cal" (calibrated) position?

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