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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
radhoo wrote ...
Dr.Kilovolt, I would need more details for the self-biasing gate circuit .
Here is my concept schematic. The problem I came to was that the circuit would need less than 1 turn on the feedback, so my idea is to use a "dropper" capacitor which forms a capacitive divider with the gate (so something in the nf range to set the peak-to-peak gate voltage to some 20 volts or even less). Becuase the gate capacitance is not constant, it might need a parallel capacitor. The upper zener diode limits the positive peak gate voltage, it might be something like few to several volts, and together with gate voltage amplitude and gate threshold voltage sets the conduction angle.
But this is just a concept and I have no idea if this will work, so try at your own risk
Registered Member #195
Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111
It looks to me that the diode prevents reversal on the fet. If a inductor was placed in series with R-start it would present a higher impedance to your feadback side of the circuit. if you could take the V+ to five or six hundred volts I think it would work well. it is basicaly the same armstong oscillator as a VTTC.
Registered Member #1779
Joined: Sat Oct 25 2008, 11:05AM
Location:
Posts: 32
Absolutely Fantastic work there. I love its simplicity and am seriously considering building one. I just have one question. How were you able to obtain the 50-100v DC required to operate the circuit? Also what is the minimum amperage required? Please help!
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Mates wrote ...
Hi Jan, what is the reason for the diode in your scheme?
Mates, the MOSFET drives a parallel resonant load at its resonant frequency so it switches a sine wave. It is quite likely that after it starts conducting each cycle, the sine wave "undershoots" the ground and goes negative for a while. If there was no diode, it would be clamped by the MOSFET diode, the energy recycled to the filter capacitor, the sinewave would get distorted and efficiency would go down.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Dr. Kilovolt wrote ...
Here is my concept schematic.
While this concept seemed like an easy victory, for some reason my first tests where unable to produce a self sustainable oscillation. In my setup everything was built in an empirical way and probably so were the results. But I hope to get another try and re-think the setup in more detail.
Meanwhile, I plan to use the secondary I've built with a different approach: a single mosfet or a half bridge, triggered by a little Atmel ATTINY45 with a pot to adjust frequency 0..20MHz.
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High Frequency Solid State Tesla Coil
