SSgap update 4-2

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

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

Hi All,

Using IF-x96 fiber optics I finally have good drive signals from the signal
generator, across the fiber, and to the IGBT gate.  The transmit LED vs.
receiver Logic signal is bellow:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/SSgap2001-4-3/Opti
cs.jpg

The turn on is less than 100nS and the turn off trails by maybe 300nS.
What is perhaps much more important is that the signals and delays are now
rock solid.  Thus, none of the IGBTs should be making the mistake of
turning on too early or too late ;-))

Using the IR2118 driver, I can really push the IGBT with solid signals.
Below is the transmit LED vs. IGBT gate voltage:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/SSgap2001-4-3/IGBT
Drive0.jpg

you can clearly see the IGBT gate turn on as a delay glitch at 300-400nS.
The IGBT turn on and turn off is within 1uS of the logic signal's command
back at the controller.  If I add 100 ohms to the gate drive the signal
softens significantly:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/SSgap2001-4-3/IGBT
Drive100.jpg

I guess that may be a good thing since the really fast turn ons and offs
may cause spikes and such that would be harmful.  The times are still well
within what is required as long as heating does not start to be an issue.

I have a picture off the prototype single IGBT and driver:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/SolidStateCoil/SSgap2001-4-3/IGBT
%2BDrive.jpg

The drain on the batteries is less than 10mA.  Note the small heat sink
that has always remained stone cold so far.

I have now run at 900volts and up to 40 amps with no problems.  I did blow
one IGBT while fiddling with the scope buttons and trying to figure out if
the collector voltage was 200 or 2000 volts...  It was 2000 ;-))  I also
popped another while turning up the variac too fast and probably with poor
drive signal.  In both cases it looks like the anti-parallel diode was
blown short.  I will have to wait till I get back to work to decapsulate
the die and see for sure.  There is a chance the diode is not taking the
powerful signals well.  It would not be hard to use an IGBT only device
(half the cost) and maybe use a more conventional but hefty reverse diode.
It is rather hard getting a lot of current through the IGBT for testing.
Even a small inductance in wiring will limit the current significantly.  I
may just resort to directly sorting the primary cap for testing.

Now that the obnoxious fiber optic and signaling problems are solved, I can
concentrate on getting the power modules woking which is the true meat of
the project and where the real challenge lies.  Everything else is
basically tested out and any further problems with the signalling and
control will be tiny.  

Cheers,

	Terry