Re: Hvguy-dot-com Feedback SSTC and New Stuff!!!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi Ken and All,

Ken, thank you for the compliments. We've worked very hard to
document our projects, so that others might look and say "cool!". We
always enjoy it.

 > Justin & Aron, you might look into my notion for using the
 > secondary's return current as the source of feedback
 > in your self-tuned systems.

Hm. So, perhaps use a current-sense resistor, opamp, and comparator?
I like the idea. The electostatic-pickup method we're using now
requires a wire, sticking up out of a box. If this "antenna" wire is
fooled with, it can cause un-healthy waveforms to go into the MOSFET
gates from the driver, so it's a little exposed.

 > And another thing: be wary of having both FETs in each half of the
H
 > being on at the same time!  You might want a bit of crossover-
 > control in the circuit to avoid that.

We keep this in the back of our mind, for sure! A commercial design
would never use a single gate transformer to directly control four
(or two) MOSFET's in a bridge, and we realize that. But, at the same
time, it works! I imagine there is some degree of shoot-through
current (we should measure it) but it just isn't hurting anything. I
made a dead-time circuit one time, it used a variable-frequency
triangle wave, fed into the non-inverting inputs of two comparators.
The inverting inputs were biased with a DC voltage...one a little
higher than the other...so the comparator outputs were two square
waves with an adjustable amount of dead time. This worked OK and I
got 10" arcs from a coil, but it was inefficient and extremely noisy.
This was probably due to the comparators being LM311...they're slow,
and oscillate when given slow (rise/falltime...like triangle waves)
input signals. For those who aren't aware, beware of old-generation
comparators! Use MAX913 from www.maxim-ic-dot-com, these things FLY.

BTW: Sparklength with our feedback SSTC is up to 12" now, with
semi-filtered (130uF) 1/2 wave rectified DC input. We're working on
making the circuit run with raw (no filter cap) 1/2 wave input, so it
can arc an estimated 20" or more. Although 8" crackling flames are
awesome too ; )

Thanks again Ken, and take care All.

Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com

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