Hi!
Through last year I've done some experiments with plasma speakers, so i decided to make a stereo version for my high school project. I've made the schematic based on this plasma speaker.
I have serious problems with the modulation section. At first i would like that the flip-flops on IO1 and IO2 are working asynchronously as shown on attached image. I'm using the flip-flops to limit duty cycle to 50%. When i turn on the modulation section it's random whether the flip-flops are running synchronous or asynchronous! This fact is making serious problem for the power section, the transformers in synchro will make huge peaks. I don't know if TL494 is capable for doing this, but i hope it can.
The second problem is if the T3 and T4 are switching load (even a dummy 15Ohm resistance load!) it sometimes disables the flip-flop function! So it doubles the frequency, the GDT cannot handle such high duty-cycle and the power section blows. I haven't found any rule when it occurs but it depends on the duty-cycle and frequency. However it's also random on which TL494 this occurs. I've detected one frequency when it doesn't depend on the duty cycle and everything works OK.
ΔV ripple of 12V source on switching single 15ohms is about 0,8V, maybe the problem is in source, but when I've changed C41 (100uF filter) to 1mF or 10mF it didn't fix the problem
I've looked on gate drivers which can stop DC coupling on GDT, but there are hard to obtain in shops here.
Although the modulation section works poorly, the sound from tweeter is great!
Thank you for help
Through last year I've done some experiments with plasma speakers, so i decided to make a stereo version for my high school project. I've made the schematic based on this plasma speaker.
I have serious problems with the modulation section. At first i would like that the flip-flops on IO1 and IO2 are working asynchronously as shown on attached image. I'm using the flip-flops to limit duty cycle to 50%. When i turn on the modulation section it's random whether the flip-flops are running synchronous or asynchronous! This fact is making serious problem for the power section, the transformers in synchro will make huge peaks. I don't know if TL494 is capable for doing this, but i hope it can.
The second problem is if the T3 and T4 are switching load (even a dummy 15Ohm resistance load!) it sometimes disables the flip-flop function! So it doubles the frequency, the GDT cannot handle such high duty-cycle and the power section blows. I haven't found any rule when it occurs but it depends on the duty-cycle and frequency. However it's also random on which TL494 this occurs. I've detected one frequency when it doesn't depend on the duty cycle and everything works OK.
ΔV ripple of 12V source on switching single 15ohms is about 0,8V, maybe the problem is in source, but when I've changed C41 (100uF filter) to 1mF or 10mF it didn't fix the problem
I've looked on gate drivers which can stop DC coupling on GDT, but there are hard to obtain in shops here.
Although the modulation section works poorly, the sound from tweeter is great!
Thank you for help
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