Re: OHVM II - Success!

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

Original poster: "David Sharpe by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sccr4us-at-erols-dot-com>

All

First successful operation of OHVM based on an analog
optocoupler!  Type I'm using is a TIL300A from TAOS
(previously TI Optoelectronics).  I  _can_not_  measure
any difference between full wave rectified signal in input
from HV (simulated with a 120/240 x 12/24 V buck/boost
transformer) and buffered optocoupled output.  Frequency
response is sufficiently fast that a line glitch from my
APC1400VA UPS can be clearly seen on signal side of
optocoupler.

Basic circuit premise is a current limiter of 5000:1 consisting
of 14.1MegOhm each side (30 x 470k, 2W, RCD CF) into
a 1N4148 bridge with 12V TVSS protection, backed-up
by two NE2 bulbs, backed up by a V130LA10A varistor.
Output of bridge feeds two low level resistors (2.82K, 1%
series referenced to ground), the developed differential
voltage across these two HV gnd referenced resistors is
routed to a differential amplifier with offset / gain adjust
(1/2 LF412).  This feeds a buffered transconductance
photovoltaic amplifier, with transconductance amplifier
to restore output on low level side.  Circuit is designed for
50kV peak +/- input (35kV rms), actual max input will be
~20kV to allow headroom to monitor voltage excursion(s)
when gap fires.  No major difficulties or design issues to date.
Only circuits left to add are:
1.  A LP filter with corner frequency of ~2kHz, to be used
      for peak detector, to prevent high frequencies from causing
      error terms in monitoring.
2.  A peak detector for displaying voltage to an analog meter
      (scaled output for a digital meter as well).
3.  Zero cross detectors for RSG firing and utility 0 crossing.
4.  Timers for (3) to guarantee proper display on RSG
      synchroscope logic.

These 4 circuits are much simpler and have consistently simulated
where the opto circuits were problematic to get a good simulation.
Estimating an analog optocoupler with two current controlled
current sources are close but no cigar, you have to build it to
confirm it.

TAOS optocoupler available from Future Electronics,
Infineon/Vishay IL300 is a suitable cross, cost for singles are
<$5.00 ea.  They have a voltage standoff of 3.5kV to 5kV
(dependent on manufacturer), which is much better then
NONE.  A very good design application note is listed on
the web at:

  http://www.vishay-dot-com/docs/83708/app50.pdf

The TAOS TIL300 info can be found at:

  http://www.taosinc-dot-com/products.htm

Now to finish circuits above, build-test isolated power supply, and
put a wrap on circuit work and start on PCB layout.  Will post to
Terry a VGA image of input and output signals being passed through
optocoupler, and breadboard stuff...

Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA