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From: palmer@tallis.enet.dec.com (Colonel Mode)
Newsgroups: sci.electronics
Subject: high voltage high frequency resonant air core transformer
Message-ID: <14786@shlump.nac.dec.com>
Date: 21 Aug 90 20:37:24 GMT
Sender: newsdaemon@shlump.nac.dec.com
Organization: Digital Equipment Corporation
Lines: 22


I've had a HVHF resonant air core transformer project on the back burner for
several years now and would like to revive it. If you're familiar with Tesla
coils, this is not one, but it's output is similar.

A high current MOSFET RF oscillator drives and is tuned to/by an LC tank
composed of 3-10 turns of 1/2 inch copper tubing and a .01-.1uF capacitor. The
secondary is several hundred turns of 20-24 gauge wire whose electrical length
is 1/4 wavelength of the LC tank frequency.

The difficulty I've been having is in the design of the RF oscillator. How can I
prevent HV kickback from the secondary from burning out the MOSFETs and/or the
rest of the oscillator? Kickback can occur whenever the load on the secondary
changes suddenly, or if the secondary is not tuned to the LC tank. I don't want
to use vacuum tubes. Someone suggested using a PWM chopper instead of a
sinusoidal oscillator, but I fear that that would only make the kickback worse.
Any suggestions?

*****
Chris Palmer
palmer@tallis.enet.dec.com
phone (508)486-6667 dtn 226-6667