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Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
I have decided to make a super high power zvs driver for my cap charger so i built a powerful zvs driver. I am using mosfets but i cant get it to work. I am using mur860 diodes and a 942c6p68k .68uf 600v capacitor. I have probed the gates and i am not getting any oscillations. Right now the input is 12v from a atx psu. I cant figure out what is wrong because i have checked the entire circuit and tested all the components and i cant find anything wrong. Here is a pic of the setup.
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
I'm not familiar with isotop packaging, but try grounding pin 4 too. Also, is the metal tab isolated from the mosfet, or connected to drain? You might want to just double check that the drains aren't shorted together, although I doubt they are. Otherwise I can't see anything wrong.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
I'll bet your pullup resistances are way too high for the massive 550nC+ gate charge devices.
Other advice I could give, just don't build the ''zvs mazilli royer flyback driver'' with those mosfets. It will be no use at all and I'm rather afraid you'll blow up the expensive devices.
If you want to drive flybacks, use some IRFP250's instead.
If you want something else, there are far better solutions for just about anything than the royer oscillator again.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Marko wrote ...
...and I'm rather afraid you'll blow up the expensive devices.
I bet they were free (dont ask why but I have the exact same devices too )
These monsters have 26nF gate capacitance, so it would be logical to use 10x smaller pull-up resistor, i.e. 47ohms. With 50V supply (these FETs could theoretically go up to 200V supply but anyway), you're going to burn 2*50^2/47=~100W in the resistors and zeners.
Like Marko said, these are unusable for the self-oscillating zvs inverter, I'm rather building a half-bridge of them powered from doubled mains (650V).
Registered Member #1107
Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792
Dr. Kilovolt wrote ...
Marko wrote ...
...and I'm rather afraid you'll blow up the expensive devices.
I bet they were free (dont ask why but I have the exact same devices too
haha how could you have ever guessed anyway now i see why they cannot be used for a zvs. perhaps i could stick with my original plans with a boost converter. In that case i will continue replying to the thread aout building a boost converter.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Your circuit will actually run much more efficiently with a pair of irfp250s than with those fets, due to the lower Rds and Qgc, and you cannot use that topology with much more than 50v in anyway due to bad oscillations. There is one member on the board (I forget who) that said they managed to make a design that uses a seperate feedback winding and some gate drivers to run at higher voltages which would probably work with your fets. Might try searching the other zvs threads to track him down.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
... wrote ...
Your circuit will actually run much more efficiently with a pair of irfp250s than with those fets, due to the lower Rds and Qgc, and you cannot use that topology with much more than 50v in anyway due to bad oscillations. There is one member on the board (I forget who) that said they managed to make a design that uses a seperate feedback winding and some gate drivers to run at higher voltages which would probably work with your fets. Might try searching the other zvs threads to track him down.
It was me, it does indeed work up to any voltage you want, but for some reason I once killed an IGBT with my feedback circuit, that was the reason why I didn't publish it because I concluded it's not reliable. Maybe the failure wasn't related to the design and there was a different problem but I don't know.
If anyone is interested, I might post the schematics.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
What is the type of transformer core martial is the ZVS driver connected to? At what freq would it oscillate if it were to do so? How much current does it draw?
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isotop zvs troubles
(dont ask why but I have the exact same devices too 
anyway now i see why they cannot be used for a zvs. perhaps i could stick with my original plans with a boost converter. In that case i will continue replying to the thread aout building a boost converter.
