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Re: Terry's DRSSTC - First light ;-))
Original poster: Terry Fritz <teslalist@xxxxxxxxxxxxxxxxxxxxxxx>
At 10:41 AM 3/6/2005, you wrote:
............
It still seems to be somewhat of a mystery as to why primary strikes
are so catastrophic to a DRSSTC. Some of my coils have survived many
primary strikes, other times just a hint of a streamer forming on the
primary will kill the thing. ...........
I modeled a secondary strike to the primary. It gave this messy event:
http://drsstc.com/~terrell/pictures/PrimaryHitModel.gif
I(Ct) is the secondary current that was at say 4 amps but it suddenly loops
down to -70A!! That is why the streamer had a bright flash to it. That
current runs back through the driver and causes the following messy things
to happen:
The antiparallel diode on IGBT3 goes in and out of conduction at 20 and 35
amps in like 40 nS pulses.
IGBT3 follows the reverse of that.
IGBT2 follows a slower current crossing path.
Not sure what IGBT1 is doing...
But all this happens in less than 100nS!! So something goofs up and it
cross conducts and blows. The high current pulse simply messes up the
timing and cross conduction in the bridge and she blows... Our little high
speed IGBT high speed current dance just goes haywire... The model quickly
crashes at this point...
Depending on the coil and exactly when the streamer hits probably has all
kinds of good and bad results... If the primary current were say 300 amps,
it would not reverse bias anything and all would be fine. But much of the
time the current pulse will drive the silicon backwards and then it is all
over... So it looks like a high current pulse from the stored charge in
the top load goes back and reverse biases the silicon at super high speed
and it looses control.
I just got my new strike rail installed ;-))
http://drsstc.com/~terrell/pictures/StrikeRail.JPG
Cheers,
Terry