RE: Terry's DRSSTC - Frequency/Pulse Width Controller

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>

>200++ amps of 100kHz is exciting, but suppose I trip the thing off at a
>current peak!

Terry,

I have been doing a fair bit of work on DRSSTC driving and I believe the
circuit I have solves this problem. It uses a PLL to lock to the resonant
frequency, and the enable/disable signal is synchronised to this with a
D-type flip-flop. So the inverter can only ever be started/stopped/tripped
out at a current zero. Of course this limits the usefulness of the
protection. The current limiting probably would only be good for dealing
with "arc to ground" type mismatches, and not a full-on primary flashover or
IGBT failure.

So I plan to avoid primary flashovers "by design" ie spacing the turns
adequately and making sure streamers can't strike it. As regards shorted
IGBTs, my aim is to use half-bridge IGBT bricks so I have to throw out both
devices if one goes anyway...

http://scopeboy.com/tesla/dw-isstc/dirty_pic.gif

(the schematic doesn't show the hand control box (circuit is the same as
Steve Ward's) or the add-on drivers and SMPS for driving big IGBTs (not
built yet))

This circuit is also highly resistant to noise because of the filtering
action of the PLL (and the fact that the feedback signal is low-pass
filtered at 6db/oct by C5, R10 to get an extra 90' phase shift to get
everything working right) I have tested it with secondary base feedback
(using current transformer L1) and primary feedback (using a CT cascade L1,
L2)

I'm working on adding current limiting to it at the moment. I guess you will
probably want to go your own way with this, but at least now you can't say
you haven't seen it ;)

BTW I see you bought drsstc.com, nice ;)