OLTC update

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi All,

I think I figured out a super simple, easy, and cheap way to control the
firing timing of my OLTC project.  In this diagram:

	http://hot-streamer-dot-com/temp/OLTC-08-07.gif

I simply put a 0.1 ohm resistor (Rsense) inline with the charging circuit.
When the current across the resistor goes negative it happens to be the
perfect time to fire the IGBT array.  The cap, resistors and diode (a 555
timer in real life) will control the ~130uS pulse width to give first notch
quenching and all.  

Here are the major waveforms:

	http://hot-streamer-dot-com/temp/OLTC-08-07-1.gif

The timing circuit automatically seeks the most powerful mode and is very
stable and reliable (at least on the computer ;-))  More importantly, such
a circuit reacts very well to odd faults like this:

	http://hot-streamer-dot-com/temp/OLTC-08-07-2.gif

I was thinking of all kinds of fancy things and ways to run the coil's
rather critical IGBT timing but they all had their problems, especially if
things we not going just right.  This new circuit is only a 0.1 ohm
resistor, an op-amp, a 555 timer, and a driver chip to run the TLP250 IGBT
drivers.

What I thought would be the most messy part of the project to figure out,
suddenly appears to be all done :-))  If this circuit and method work, it
is a major breakthrough!!

No more major technical stuff to figure out now.  Just have to build it and
see if it really works...

Cheers,

	Terry