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Registered Member #1940
Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34
Hi
I have question about my plasma speaker. I have built my third plasma speaker a few weeks ago. This third plasma speaker is a frequency modulated plasma speaker designed by Jan Martis. This is the following schematic.
I’m very impressed by its performance and quality. But the spark length is a bit too small. This is because the input voltage I use is 34V. The fly back sees only the half of the input voltage, causing a small spark. Somebody told me that it was a better idea to use a full-bridge output stage. A full-bridge output stage should be more powerful and the fly back should see the full input voltage. So I did some researche and drew the following schematic (it is a bit messy) Is this going to work? Or am I making a mistake somewhere?
Registered Member #1875
Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635
Looks conceptually sound, but you may also want to place a film capacitor in series with the flyback primary like you did with the gdt. You can also remove the gap from the flyback transformer with this topology.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Hello, yes ysou should put the film cap in series with primary (~1-2 uF). That is the old design of my plasma speaker which uses frequency modulation, my new design goes back to pulse width modulation.
Registered Member #1940
Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34
Thanks you both for the answers! This should be the improved schematic.
I still have some remaining questions. Why do you want to place a capacitor in series with the flyback? I have been thinking about this. The only explanation I came up with is the following. In case of a pulse that is way to long, you create a short-circuit if you don’t use a capacitor in series with the flyback. So the capacitor is a safety device. Am I right?
Then I have another question. I have been looking on the internet to find the difference between a flyback with or without a gap. I couldn’t find an answer to that question. Can you help me out? What is the gap in the flyback anyway…..
Theoretically speaking, a PWM modulation should indeed be better then a FM modulation. I love the way the output stages of the FM modulation work. But I haven’t figured out yet how to combine this output stage with a PWM modulation. I have still loads of things to learn before I can design a schematic of my own.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
The capacitor softens the load for the mosfets. Instead of a direct off to direct on, like a square wave, the capacitor "rounds the corners" for lack of a better way to say that.
Registered Member #2919
Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652
In the best case, the capacitor and leakage inductance of the flyback resonate at the frequency of the driver, soft-switching happens, and the MOSFETs are in happy land.
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Full-bridge plasma speaker
