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Registered Member #7362
Joined: Fri Oct 19 2012, 06:10AM
Location:
Posts: 3
Hi, I am trying to build a singing class E tesla coil. I want to modulate the high voltage(around 150v) based on an audio signal, so that the power supply is varied based on audio signal. Is there a method where I can achieve this without burning much power across transistors. I was just thinking of turning on-off a transistor based on Audio Input.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
When you say transistors, are you referring to the modulation side of things (i.e. modulating the drain voltage to the Class-E) or the entire circuit.
The Class-E switching is pretty efficient, however, you can go one step further and use Class-H modulation. This is similar to Class-E except that the supply rail is also modulated vs. the audio input level.
Richie Burnett has posted links to articles on Class-H topology before. If you search the archives, you could probably find something.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I think that he wants to modulate the bus, using another amplifier.
The easiest thing would be to buy a beefy audio amp, one designed for 200w or so into 16 ohms should work. You also need to figure out a way to deal with the DC bias issue, since allmost all audio amps are AC coupled, so you can't drive a bridge from them! You should be able to just add a big honking inductor in series with the DC supply (something like the secondary of a MOT would probably work decently well, it is just a choke so core losses at high frequencies shouldn't be a problem), and then connect the amplifier output across the coil. If you put 80v DC into the coil and then have an amp which puts out +/-80v (400w pk specified into 16 ohms, or 800w pk specified into 8 ohms) you can get a 100% modulation depth 0-160v. You can probably get away with a much power power amp, even 100w or so should be plenty. Just be extremely careful with the grounding, there are no promises made that the decoupling cap is on the + terminal or that the - terminal is at ground.
If you want to build your own, class AB or B isn't all that bad and fairly simple, but you will need to go to class D or H if you want to get into the <80% efficiency range. If you want to go all out you can simplify the situation quite a bit and go single ended, although that that point the only way to help your efficiency is going to class D or H since you have to pass all of the coils current anyway.
Registered Member #7362
Joined: Fri Oct 19 2012, 06:10AM
Location:
Posts: 3
Yes you are right, I am looking forward to modulate the 150V Bus. Also if I am looking to build my own amplifier, is class D or H the only method to do that, or are there any other simpler methods.
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Modulate 150V at Audio Frequency
