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Mazzilli ZVS Driver driven from more than 40V (how many times has this come up?)

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Dr. Shark

Wed Apr 25 2007, 12:03PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

For some reason I missed this thread, so I have to revive it now.
Sulaiman, how did you come up with the .2-.3T maximum field for ferrite? I usually regarded it to be more like 1T for ferrite and close to 2T for iron in my calculations. My line of reasoning is that most transformers do not go anywhere close saturation, because hysteresis losses would become significant. For our hobbyist designs however, loosing a few Watts does not matter, so we can actually go right up to 99% saturation.

Sulaiman wrote ...

From my little experience with this kind of circuit;

1)When using separate supplies for power and gate-drive
the gate-drive supply should be connected first, then the main power.

2)The ferrite core must not saturate, how to calculate that?
2.1) Integral of V.dt = Vpk.(PI/8.F) = Vdc.PI.PI/8.F (V.s)
2.2) Peak magnetic flux = Phi = B.Ac (Wb)
2.3) (Integral of V.dt)/N = Phi = B.Ac
Vdc.PI.PI/8.N.F = B.Ac
so
N= (Vdc.PI.PI)/(8.F.B.Ac)

e.g. Vdc=50V, F= 20 kHz, B= 0.2T, Ac= 200x10-6 (core area, 200sq.mm)
so N= 77 turns! (38.5+38.5 turns)
you could push it to 0.3T peak flux density for 26+26 turns
or operate at a higher frequency, 50kHz= 30 turns.
or use a larger core...etc.etc.

If you use less turns than calculated using the above, then the core will saturate
for very little extra output.

Marko

Wed Apr 25 2007, 12:09PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hm, 0.3T is what is mostly considered as a max for ferrite...

But I just recently pushed some of my cores in royer to some 0,5T and I couldn't see much of difference, but the core did get warm.
I think calculation for 0.2-0.3T is right ballpark.

Dr. Dark Current

Wed Apr 25 2007, 02:13PM

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

joe wrote ...

Sulaiman, how did you come up with the .2-.3T maximum field for ferrite? I usually regarded it to be more like 1T for ferrite and close to 2T for iron in my calculations. My line of reasoning is that most transformers do not go anywhere close saturation, because hysteresis losses would become significant.

I don't know how this represents "most" ferrite transformers, but core of the flyback in my old TV would operate EXTREMELY hot, probably as hot as 150Â°C or more. Once when the TV was switched off for about a minute, and when adjusting something I accidentaly touched the core and got burnt.

r3d

Tue May 01 2007, 09:14AM

Registered Member #532 Joined: Sat Feb 17 2007, 05:00PM
Location:
Posts: 11

Back on topic: I tried 56V on my Mazzilli and didn't get much longer sparks than on 40V!

Ocean Waves

Tue Nov 22 2011, 08:07PM

Registered Member #4181 Joined: Thu Nov 03 2011, 02:39PM
Location:
Posts: 42

your 56 volt psu may have been bogged down to 40 v by the load so unless you really masured 56 volts while it was operating we will never know, but I think you should have gained arc from 40 to 56 noticable unless you where pushing maximum power transfer than you are only really going to notice the gain in the distance it takes to strike an arc, each flyback has its limits of how much power it can pass with a partucular tank circuit, you will like have to change the tank circuit to a value closer to that of the core to get any more proformance

it is best to have your cap soldered right to the inductor on the core, all of the designs that have it soldered to a pcb are in error this way and it causes a lot of fets to emit fire from the drain when the circuit is stressed..........

it makes a huge differance where the cap is placed, with the cap directly on the core with less then 12 mm of leads you get huge proformance. With the cap on the pcb with say 10 cm or more of wire connecting the core and the cap significent current limiting takes place through detuning, while this makes for lesser proformance it does have the advantage of making a less stable cooler running driver, for say making Ozone on your desk and burning stuff casualy???

however this lesser proformance comes with the risk of blowing mosfets seems that the furthur away the cap is the more often, the circuit stops osclating when a load change accures that effects the tuning, like say from flaming arcs to a large corona area and it becomes nessassary to have a power supply that cannot shoot the fets......... such as one that can only supply a peak of 10A and you better be there to bounce the power to keep from melting down from dissipation.........

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