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Registered Member #855
Joined: Sat Jun 23 2007, 05:25PM
Location:
Posts: 8
EasternVoltageResearch wrote ...
Actually, if you are looking for SSTC audio modulation - were you referring to a plasma speaker type reproduction (full bandwidth audio) or the buzzing audio tones commonly seen in DRSSTC audio modulation? If its the latter, then thats the zero cross circuit.
If its full-bandwidth audio modulation you need, then simple PWM of the gate drive is all you need. This can be done as simply with a single 555 timer IC or similar IC such as TL494.
I don't think the SSTC that I linked can handle full bandwidth (that would mean %100 duty cycle right?). If I can get some good heat sinks, and the circuit can handle plasma production, then I might try and change the schematic for full bandwidth audio, but for now im going to try and do the buzzing audio.
Registered Member #4104
Joined: Fri Sept 23 2011, 06:54PM
Location: Uk .
Posts: 122
I used a 4046 PLL for a audio SSTC , Due to the CW running i warped my acrylic secondary from the heat :D these are the results i got with the 4046 based SSTC - :)
My SSTCs (based on Ward's Mini SSTC5) have been running solid with no problems other than primary heating for quite some time now, yet audio modulation always seems to be out of reach.
I've been using a SG3525 to deliver audio PWM to the UCC gate drive chips' enable pins, but have not found a suitable switching frequency for the PWM.
The SG3525 maxes out at 100KHz, so I can't go up to the coil's resonant frequency of 185KHz. However, I have tried everything from 25KHz to 99KHz and still no suitable results have been attained. The output power of the coil seems inversely proportionate to the switching frequency of the audio pwm. Likewise the sound volume produced is also inversely proportionate to the switching frequency. At 99KHz I get a very quiet, almost inaudible modulation, and coil output is reduced to nearly 4% of normal. The sound is clean though with no distortion other than an incredibly high high-pass roll off effect, with audio freq below about 1KHz completely lost. At 25KHz audio pwm switching the coil's output is up to about 7% of normal, and the audio modulation is definitely audible, but not by any means loud. There is decent bass response but there is also significant distortion... in fact the audio sounds quite horrid!
So, what would you suggest I use, or what means to determine, for the proper switching frequency?
Registered Member #7267
Joined: Tue Oct 16 2012, 12:16AM
Location: Detroit, Michigan
Posts: 407
Sigurthr, in your case I would just try to come up with new secondary (optional toroid) dimensions to be more in the frequency range of your PWM. That way, any changes to your PWM design would be minimal to none. I'm not positive that would solve the problem, it might. This is just an estimate, but maybe a secondary that is 4.5" diameter x 18" tall with something like 30awg, with a small toroid would bring the frequency closer to your PWM switching frequency
So the audio PWM switching frequency has to be close to the fres of the TC? Well that would explain a lot if so. I'd rather just build a simple 555 audio PWM in that case. Oh and my secondary is 4.3 x 18 with 30ga and a 12 x 3 Toroid, haha!
Would phase mismatch of the audio PWM and the drive signal cause any problems?
Registered Member #9925
Joined: Wed Jan 30 2013, 08:07PM
Location: Rochester MN
Posts: 7
My PWM uses the sg3525. I use a cheap MP3 player to audio modulate the 55khz the chip is set at. This signal then goes through ucc driver chips, GDTs, and full bridge. My secondary is around 300mH. It is 33awg wound on a 7.8" form (sono) aproximately 15" long. If you decide to stick with your PWM, you might have the option of using pin 3 of the sg3525 to sychronize a primary feedback
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Singing Tesla Coil
