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Piernas's Fast ZVS Mazzilli Driver (mod for high frequency&voltage)
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Neukyhm:
Hi again everyone, I'm releasing part of my project https://www.eevblog.com/forum/projects/x-ray-machine-constuction-(project-finished)/

Do you want higher voltage with your transformer (e.g. TV flyback)? Just make your primary with less inductance (less turns). But you will see that the original Mazzilli driver will have to work at higher resonant frequency, and it may fail. This version of the Mazzilli driver solves this, allowing higher frequencies so you can make your primary with much less inductance and increase the output high voltage. Also because the switching is done by IC, it's much faster and the Mosfets will pass the ohmic region quickly so they will be colder.

I put a dual Mosfet driver in the middle and now the circuit is much faster at switching, allowing higher frequencies and voltage. This is great since the original circuit have some 470ohm resistors that make the gate charging process very slow.

More info can be found on the project page at hackaday.io: https://hackaday.io/project/162935-piernass-fast-zvs-mazzilli-driver

The benefits you get using this are:

-Higher DC voltage input
-Higher AC voltage output (because you can make a primary with less turns)
-Colder Mosfets, because the switching is very fast
-Higher frequency
-Lower primary resonant current
-Negligible power lost through the UF4007

I designed this because I had to drive my custom HV ETD59 gapped core for the X-Ray machine, but my primary's inductance was so low (3+3 turns) and my caps so small (136nF) that the resonant frequency was 110kHz. The original ZVS driver just blows up the Mosfets (true story).

I think this can be very useful for those of you that want to build a high voltage transformer and don't know how to drive it. Hope you like it :P
flyrod:
Thanks for sharing your design!  How did you pick your driver IC?  Would any CMOS input driver work for this?

Also, did you record any waveforms of the input or output of the gate drive?  The tank waveform looks like it has some parasitic oscillations maybe.
Neukyhm:

--- Quote from: flyrod on December 23, 2018, 10:39:33 pm ---Thanks for sharing your design!  How did you pick your driver IC?  Would any CMOS input driver work for this?

Also, did you record any waveforms of the input or output of the gate drive?  The tank waveform looks like it has some parasitic oscillations maybe.

--- End quote ---
Picking the IC was difficult. I spent a lot of time searching on RS Components until I saw this IC and I liked the datasheet.

Yes, the IC must be CMOS, because the UF4007 has a voltage drop of 0.8V (worst case) and TTL signals have transition level of 0.8V, so you want a CMOS driver with hysteresis, like the TPS2814.

I do have some input waveforms but I don't know where they are  :-BROKE I'll look for them. But yes, there is noise exactly at the time the Mosfets are switching. I'm sure it's because when they are switching we can't consider that one of them is fully On, so we have a current through the 100uH inductor that wants to scape though a fully On Mosfet, but because they are switching and none of them is fully On, that current through the indcutor causes a small voltage peak to both drains that also blocks both UF4007, that's why there is a bit of noise and that's why I put those two 100ohm resistors before the diodes, they delay just a bit the turning off process of one of the Mosfet so the other one has time to turn On, and the current through the 100uH inductor is not reduced so much and that voltage peak & noise are lower.

This only happens at switching Mosfets, because the reason above, but the driver will work fine.
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