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Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
I thought of an idea;
Looking around at Steve's QCW little coil, and the way it operates, perhaps there could be some thought into a buck regulated tesla coil.
Feedback would be taken from the primary resonant circuit, charging a cap through a low pass filter and a voltage divider of some sort to allow feedback via Op amps. Then all you would need to do to change the spark length would be to change the voltage reference of the op amp!
Plus, it could possibly give the "ramp" that the QCW requires, if you use a small enough filter cap on the buck converter.
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Yes, I want to say it is, but I would like to try it with an actual circuit...
Mains Buck converters haven't exactly worked well for me, (probably due to poor regulation, and/or no minimum load...) and I'm wondering if there's any alternative, or perhaps some other design that could give a ramp? (I don't think forward converters give ramps, do they?
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
what about regulating the bridge with PWM? There would be a problem with feedback though, either you would need to run fixed frequency, or make some kind of a voltage controlled "pulse shortener" (shouldnt be that hard to implement though)
Registered Member #3637
Joined: Fri Jan 21 2011, 11:07PM
Location: Buffalo, NY
Posts: 1068
Dr. Kilovolt wrote ...
what about regulating the bridge with PWM? There would be a problem with feedback though, either you would need to run fixed frequency, or make some kind of a voltage controlled "pulse shrotener" (shouldnt be that hard to implement though)
It sounds like it could be done with a 4046 and an op amp...
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
Inducktion wrote ...
Dr. Kilovolt wrote ...
what about regulating the bridge with PWM? There would be a problem with feedback though, either you would need to run fixed frequency, or make some kind of a voltage controlled "pulse shrotener" (shouldnt be that hard to implement though)
It sounds like it could be done with a 4046 and an op amp...
More voltage on the VCO, etc etc
PWM'ing the bridge has been talked about (see e.g. "PSQCW DRSSTC" in the projects section; also, I think Steve Conner was talking about delta-sigma modulation on the bridge a while back). However, no one has done it yet, so your mileage may vary.
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Dr. Kilovolt wrote ...
what about regulating the bridge with PWM? There would be a problem with feedback though, either you would need to run fixed frequency, or make some kind of a voltage controlled "pulse shortener" (shouldnt be that hard to implement though)
Well, for lower frequencies that go along with IGBT's resonant modulation technique is far superior over PWM (and curiously easy to implement as it appears!)
For very high frequencies, I think the modulation of choice would be phase shift control. This way two half bridges could be used to regulate power while still keeping perfect class DE operation.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
I started building something like this last year, but never finished it. This was before I noticed that other people had already thought of it, under the name of 'QCW' coils, etc.
My (unfinished) setup simply consists of rectified mains to form a DC link with a high capacitance (with power factor correction!) , and then a PWM'd chopper circuit, with the PWM coming from the CAPCOM of an AVR microcontroller that contains a waveform look-up-table. There's no feedback currently, it's just a microcontroller controlled voltage source - so if my look-up-table was of a half wave rectified sine, and I played it back with a LUT advance rate of 20mS per cycle through the LUT, then my TC would behave as if it were running from halfwave rectified (50Hz) mains.
I know what you mean about the TC losing feedback during zero output portions - my method of getting around this is to apply a small DC offset to the TC's H-bridge - of say 20V. If your TC's feedback signal is good, then it should be already clipping anyway at this low power, and will continue to clip just the same as the power is increased.
The purpose of this project was to eventually try different input waveforms to the bridge to see how they effect spark length and pattern (a sort of continuation of an article on Richie's site if anyone has seen it) and a bonus feature of this unit is that it can be modulated with an audio input I think heat is going to be the biggest problem, I was aiming for around about 1kVA but I'm also trying to cram it all into a small ex-power supply case, the sort used for those 13.8V 3A CB radio supply units...
Registered Member #2292
Joined: Fri Aug 14 2009, 05:33PM
Location: The Wild West AKA Arizona
Posts: 795
Avalanche wrote ...
I started building something like this last year, but never finished it. This was before I noticed that other people had already thought of it, under the name of 'QCW' coils, etc.
My (unfinished) setup simply consists of rectified mains to form a DC link with a high capacitance (with power factor correction!) , and then a PWM'd chopper circuit, with the PWM coming from the CAPCOM of an AVR microcontroller that contains a waveform look-up-table. There's no feedback currently, it's just a microcontroller controlled voltage source - so if my look-up-table was of a half wave rectified sine, and I played it back with a LUT advance rate of 20mS per cycle through the LUT, then my TC would behave as if it were running from halfwave rectified (50Hz) mains.
I know what you mean about the TC losing feedback during zero output portions - my method of getting around this is to apply a small DC offset to the TC's H-bridge - of say 20V. If your TC's feedback signal is good, then it should be already clipping anyway at this low power, and will continue to clip just the same as the power is increased.
The purpose of this project was to eventually try different input waveforms to the bridge to see how they effect spark length and pattern (a sort of continuation of an article on Richie's site if anyone has seen it) and a bonus feature of this unit is that it can be modulated with an audio input I think heat is going to be the biggest problem, I was aiming for around about 1kVA but I'm also trying to cram it all into a small ex-power supply case, the sort used for those 13.8V 3A CB radio supply units...
This is basically how the QCW operates. I use a regulated delta modulator. Not so much PWM but frequency modulation. The reference on it can also be any signal from 0 to 5 volts. Including audio
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Buck Regulated Tesla Coil
I think heat is going to be the biggest problem, I was aiming for around about 1kVA but I'm also trying to cram it all into a small ex-power supply case, the sort used for those 13.8V 3A CB radio supply units...
