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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I have been experimenting with single MOSFET flyback driver (tl494+mosfet). I could get about 30kv from a small flyback with frequency below 15khz. That was nice, but my ears did really hurt from the horrible whistling sound. When I upped the frequency above audible range, the output voltage decreased (logically). I wanted it to be the same as previously, so I removed some turns from the primary in hope to increase the output voltage. However, whatever I did (vary duty cycle, change primary turns), I did not bring the output voltage even close to as with lower frequency. So the question is, WHY I cannot get so high voltage with higher frequency? Is there something I can do to increase the voltage (change core airgap maybe?) thanks, J.M.
Registered Member #540
Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
Probibly the flyback's resonant freq was near 15KHz so when you increased the freq then it went out of resononce. Yeah making the airgap larger in the flyback core will decrease the inductance thus raising the resonant freq.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Wow, I'm now getting maybe 50kv from a small poor ac flyback! What I did was to increase the airgap maybe 3 times and I also put a resonant capacitor on the primary, it's resonating above audible range, but the problem is now that whenewer I connect anything to the output, it drifts out of resonance and the voltage drops.
Has anyone have an idea how to make this circuit self-resonant? Feedback winding? Secondary return feedback? Antenna? I seem now to have a Tesla coil-like problems
Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
Nice, I didn't know that about the air gap, I'll have to try it sometime.
Concerning making the circuit self-resonant, I made this on Friday. Its not done yet, as there is still an issue with the high side mosfet floating, but the concept should work. It is supposed to act like a SGTC, except solid state. When circuit starts the top mosfet will conduct until capacitor C is full, at which point it will close and the bottom mosfet will open. That allows the LC oscillation to go, which the flyback primary being L. When capacitor C voltage sinks to a certain point, the process repeats itself. Or at least that is what I meant for it to do.
Registered Member #549
Joined: Sun Feb 25 2007, 02:49AM
Location:
Posts: 11
In ZVS Driver, how much bigger number it of turns in the primario of flyback, and greater the value of the capacitor, greater goes to be the chain and lesser it goes to be the frequency in output high-voltage?
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Flyback output voltage vs. frequency
What I did was to increase the airgap maybe 3 times and I also put a resonant capacitor on the primary, it's resonating above audible range, but the problem is now that whenewer I connect anything to the output, it drifts out of resonance and the voltage drops.
