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Micro Solid State Spark Gap Results



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

List

I posted this information to Terry Fritz earlier, thought I
should post, if for no other reason to stimulate the
imagination...
--------------------------------------------------------
Had to share work I did this week, if of interest will take
more readings and post to population on the net...

We test a proximity inductor in a proprietary system we
are building.  Rather then test statically (with a LCR meter,
ohmmeter, etc.) I suggested building an impulse tester to
ping the coil, and look at decrement wave.  It is exactly
the same as a CDI discharging through a SS switch.  We
were using a manual switch.  So what I cooked up is a
555 monostable (250ms ON time) capacitive coupled
from a I/O line to trigger it.  The output drives the base
of a 2n3906 PNP transistor across a Toshiba
TLP250 high speed optocoupler.  It is powered by (2)
9VDC floating power supplies.  The charging cap is a
100V pulse rated polypropylene, 100nF (0.1uF);
inductor is 4-5uH nominal, so ring frequency is in the
200-250kHz range.  Switch is a pair of IR IRL3803
30V, 120A, 0.006 ohm logic drive FET's wired S to S,
G to G (drive between G to S; +/- 9VDC) and switch side
is one drain to - of charging supply (ground) and opposite
drain to node of charging cap and charging resistor.  Input
charging VDC is 12V, charging resistor is 1k ohm.
Inductor is wired to opposite side of capacitor to ground,
through a test fixture, to allow manual now, possibly ATE
testing later.

To operate, FET gates are normally -9V, trigger 555,
optocoupler turns on for 250ms, which turns 2n3906
off, which allows TLP250 to turn on.  When TLP turns,
on GS voltages shifts to +9V, biasing both FET's ON for
250 millisecs.  I did this so oscillation passes through a
anti parallel diode and series FET with each half alternation
for symmetry and unified losses.  This was very successful,
ring wave was absolutely classic with no distortions or
offsets, and repeatable frequency (max.deviation was
<2kHz max. to min. on 20 repetitive operations).

Peak voltage on decrement wave is ~11.9V, Vdrop peak
across switch is approximately 0.35V, that's a voltage drop
of only 3% (power loss of less then 0.1%!!!), Zo ~7 ohms,
peak current about 1.5A.  Ring wave oscillates about 30-40
cycles can remeasure to get typical info.  Turn on / ring up
time is less then 1/4cycle.  Even put bi-directional LED on
gate of FET's, green OFF, red ON-- confirming bipolar
operation of optocoupler..

I know this is very preliminary, but I've simultaneously:
1. Validated isolated driver for SS Variac
2. Validated basic concept for SSSG (ibeit at very small
     powers ~20W peak)
3.  Only mild warming after popping unit manually 40-50
     times in about 45 minutes was observed; but note, the
     TO220 FET's are mounted to the PCB with NO HEAT
     SINK.
4.  Power loss for a first PCB looks absolutely impressive!!!

What a Friday at work (and they pay me
to do this; WINK WINK)!

Regards
Dave Sharpe, TCBOR
Chesterfield, VA. USA