HV Generator

[T3sl4co1l]

Going to be doing some highish voltage experiments soon, so I'm going to need something like this:



Linear controlled Royer oscillator, typically runs around 60kHz.  Adjustable 220-2070V output.  Seems to be fairly low ripple, but there may be some instability under certain operating conditions (~half scale voltage, half to full load?), which I think has to do with either parasitic instability in the oscillator itself, or RFI pickup by the poor LM358.

Don'cha just love how professional it makes things look, just having that damned yellow tape handy?



Efficiency ranges from 10-20% at low voltages up to 60, maybe 70% at full voltage.  Good for 5-10mA (varies by voltage), so yes, watch your fingers ladies and gentlemen!

At full output, I can draw a pretty reasonable "medium temperature" arc, using a 50k 5W (wirewound) resistor for current limiting.

Tim

[mathias]

Nice! Very interesting to see how you've done it.

If I'm reading your schematic right, it's linearly regulated, but limiting the current. Have you tried anything new with this converter, like switch mode regulation?

[SeanB]

Even more professional if you use varnish to hold the tape down. Very nice build there.

[T3sl4co1l]

Thanks!

Haven't screwed with it, no.  It would be possible to drive from a buck, using a sufficiently large inductance (and a frequency either orthogonal to the oscillator's, or directly locked to an even harmonic -- dunno which would be better), in which case the circuit overall is exactly the same (including the regulator section), except you have a pulse width modulator and driver replacing the follower.

The oscillator isn't the best approach for wide range; it gets squirrely at low settings and light loads, since even if the supply goes to cutoff, the gate bias remains (which is sufficient to develop a few hundred volts on its own).

The Jim Williams solution might be to run it at full power, and pass or shunt filter with an Eimac 25T -- at even more cost to efficiency, but it sure would be simple and robust.

Tim