Re: SISG Quench Circuit

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Terry,

I've ordered some IGBT's and heatsinks (just getting started 
collecting parts). Observing the schematic, I was looking at the 
"basic scheme" of the SISG. In a nutshell, the scheme is simply to 
use the collective sidad transient level to fire the IGBT gap! How 
cool is that! I'm impressed with a transient device being used as switch!

The IGBT's I'm getting are the ones mentioned on the list a day or 
two ago (150 kHz). I found Mouser sold them individually where all 
the other suppliers were bulk (450!). Mouser was a dollar more, but 
sold low quantity. I bought 4 and will likely do something a bit 
different with them. I kind of want to vary pulse rep to the gates 
and parallel the gates for current, so maybe I'll do something else. 
I don't know yet, just thinking.

With IGBT's gaining on switch times, there is a great deal of fun to 
be had with SSTC's!

Take care,
Bart

Tesla list wrote:

> Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
>
> Hi All,
>
> There has been work going on behind the scenes on an SISG circuit 
> that can do quenching.  All "pie-in-the sky" and nothing is 
> "actually tested".  The circuit of the "moment" looks like this:
>
> http://drsstc.com/~sisg/files/SISG-Quench-02.gif
>
> Basically, the standard SISG circuit (same reference designators now 
> too!) with the following changes:
>
> 1.  R4 is just 2.2k now.  This is sort of a "last resort" resistor 
> that will shut the SISG down incase something does not go right.
> Normally, the quench circuit will shut it down far earlier.  Without 
> it, the drive voltage could be at say 7 volts "forever"!  Like when 
> it is off and on the shelf...
>
> 2.  R5 is variable now from the SISG turn on timing thing...  This 
> might turn into a fixed resistor if a perfect fixed value can be 
> found.  Prolly could be 50 ohms...
>
> 3.  R6 and C2  form a voltage ramp that slowly charges C2.  At 12V 
> plus the 0.55 volt SCR threshold, The SCR will fire and force the 
> gate circuit drive voltage down to ground, turning everything 
> off.  D2 was added to give a "nice" mid range voltage trigger 
> level.  The quench time is 7.12e-9 x R6.
>
> 4.  R7 provides the "override" function.  If the "mess screws up" 
> and there again is more than 900V across the SISG, The SIDACS will 
> re-fire and the IGBT gate will turn "right back on" even if the SCR 
> is firing.  "Nothing can go wrong" :o))  Useful in an "emergency" 
> :D  But in this state, the quench will still react "fast" once the 
> current/voltage drop, so the quench should "still work".  Sort of 
> cool!!  C2 is a 1% timing cap that DK sells cheap ;-))  But there is 
> no guarantee that multi sections will decide to shut down at 
> "exactly" the same time.
>
> 5.  It is a two terminal add-on thing, for testing at least.  It is 
> a simple added mod.  If it sucks, it can be easily removed too :o))
>
> 6.  There is a tiny danger that if you set R6 to zero ohms that you 
> will blow the SCR.  But the SCR is a dumb 40 cent part and not worth 
> adding another resistor to protect it.  If you set R6 to zero ohms, 
> "you is bad" ;-))
>
> Quenching will probably not make a great spark length difference 
> (but maybe a little) it might cut the IGBT heating in half (not a 
> big deal though).  But It seems a "popular" thing that seems fairly 
> easy to add.  I think this circuit will do it without breaking anything.
>
> If it is "cool", it would be simple to add to my new SISG timing 
> program too. :o)
>
> Cheers,
>
> Terry