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I'm currently trying to build a 4MHz Tesla Coil powered by a Class-E amplifier. I've managed to design and simulate such amplifiers with a load consisting of a resistor and a coil or a capacitor using this paper from Sokal. But the load I actually want to drive looks like this:

and has impedance completely dependent on the frequency:

(The resonant frequency isn't exactly 4MHz, because I didn't use exact values)

My approach was to find an equivalent circuit only consisting of a resistor and a coil or capacitor. But this is very hard, because at the point where I want to operate it, the impedance is very sensitive to changes.

Additionally to that, since I don't have infinite QL, the output signal contains a lot of harmonics, so I can't even make an equivalent circuit for a single frequency.

If anyone has in idea how I could design my amplifier to work with this load, any help would be appreciated.

PS: It is certainly possible to do this, as this and this project shows. They just don't go into much detail and I wasn't able to contact the authors.

ismxy
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  • The point is that the load impedance is varying so rapidly that you don't want to build an amplifier, but an oscillator with a class-E output stage whose frequency is controlled by the impedance slope of the coil. Bear in mind that arc loading of the coil will significantly change its effective C1, so you have to let the operating frequency be dictated by the instantaneous C. – Neil_UK Nov 03 '21 at 15:07
  • Thanks, but class-E has a very narrow range of operating frequencies, right? If I design it for 4MHz, it will only work for 4MHz. Also, the two projects I mentioned above didn't do that, but used a signal with constant frequency. – ismxy Nov 03 '21 at 15:27
  • Am unsure of **720u9** value for L2 (perhaps 720 uH?). If so, the Q of the transformer secondary when treated alone is over 1000: that's suspiciously high. – glen_geek Nov 03 '21 at 18:30
  • It's 720.9μH. The Q factor is probably that high, because the secondary side is just a coil with it's wire resistance and parasitic capacitance. – ismxy Nov 03 '21 at 19:29

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