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SISG Quench Circuit

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:


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)