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Re: ISSTC Components

Original poster: David Sharpe <sccr4us-at-erols-dot-com> 

Hi Steve, Dan, Malcolm


>Then a kind person
>> > the States gave me a copy of Sargent and Dollinger's "High Power
>> > Electronics" and I saw "my" wonderfully innovative scheme described
>> > in graphic detail and written up long before I hit upon the idea.
>Yeah... thats starting to happen here as well.  Dan McCauley has been 
>looking for SSTC history and indeed others have done similar to what i have.
>> > That's not to belittle your achievement in any way but just to make
>> > known that an exhaustive search for prior art is not a bad thing
>> > before making claims of originality.
>Agreed.  but...
>IF people had done such things in the past, why is it that people are 
>amazed when these new SSTCs are more efficient at making long sparks that 
>spark gap coils???  I mean... SOMETHING is different here ;).
>Did the technology exist 10 years ago but somehow was forgotten?

The key point is as I have stated some years ago (2 or 3 at least) , that 
circa 1990-95 there
was NO _solid state_  power devices commercially available (salvage, used 
industrial, new)
that could handle pulse MEGAwatts of power that was within the reasonable 
realm of
ACADEMIA (read big science), must less us "poor, dumpster diving 
(and I do include myself in that list...   :-)  ), without "massive" 
parallelism, N+1 redundancy,
and associated mechanical problems (voltage hold off, mounting labor, 
minimal inductance
wiring, etc.).  There were darlington transistors of perhaps 1-1.2kV but 5 
to 10X slower
then standard available IGBT's currently being supplied, with maximum 
currents in the
500-600A range.  I'd like to see the fireball if someone tried to use a 
darlington in an
OLTC application (behind a lexan blast shield).   Duane Bylund did build 
the first
documented half and full bridge SSTC working off AC power line in Popular 
(and his follow on book Modern Tesla Coil Theory) using 600V bipolar 
and proportional drive with a Baker clamping system between the collector 
and base.
A high power full bridge unit was also documented (~1kW power processed) 
but had
a much lower MTBF due to shoot through, dead-time issues.  This work was in the
1993,94 time frame I believe; I have a copy of his book around here 
somewhere and
can provide a publish date/ISBN if needed.

First and second generation IGBT's available back then also had an ugly 
habit of latchup
with gate overdrive (don't even dream of +/-30V drive).  One device that I 
thought was an
excellent potential (no pun) pulse power candidate; but died on the vine 
was the MOS
Commutated Thyristor (MCT).  High pulse powers of an SCR, can be gated off 
with a
negative pulse, but a voltage controlled device similar to an IGBT, quite 
different then a
Gate Turn Off Thyristor (GTO) that has low cathode gain (i.e. you need to 
divert ~1/5
conducting cathode current to turn device off).

If you think I jest, consider Greg Leyh's heroic exploits in Z transform 
pulse power at SLAC
in trying to replace 30yr + vintage thyratrons with IGBT's.  At least with 
a OLTC, you are
starting from a current 0 versus a hellish di/dt in conjunction with a 
simultaneous dV/dT
application  in the klystron drive network.

There has been continuous (nearly exponential) improvement in all metrics 
of power
devices since the mid 1990's.  As a tip of the iceberg example, show me a 
schottky diode capable of Vrr ratings above say 200V (don't exist!). Now SiC
(silicon carbide) devices from Cree are becoming available with Vrr of 
600V, 1-1.2kV
in development with 10's to 100's of amp capability!!!  And can handle junction
temperatures way beyond that of silicon devices.

>> >
>> > Malcolm
>> >
>> >
Best Regards
Dave Sharpe, TCBOR/ HEAS
Chesterfield, VA. USA