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SISG firing timing program

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Russ and All,

I made a program to look at the SISG firing timing. With this program, the Gate resistor (100 ohm R5) can be adjusted for faster firing if needed. For my next coil, I am dropping it to 50 ohms so the IGBT kicks in faster. The old value of 100 ohms was a wild guess...

The file is at:


There is a PDF file in the zip with the instructions and source code.

In general, one should try to have the IGBT TakeOver Time twice the Main Capacitor Charge Time. That way the main timing cap is 'sure' to be fully charged before the IGBT takes its charging current away. The Primary TakeOver Current should be less than 100 amps too so the SIDACs don't get too beaten up.

The SIDACs take about 124nS to get going and that time is not significant since no real current flows, so it is ignored. The 24V TVS has a pretty nice overshoot too (28V) that could be set in the input file if you want. In the real world, there will be resonances, propagation times, impedances, Emitter inductance, etc. but the program matches the scope stuff pretty good where it counts.

It might be possible to come up with a resistor value for R5 that would do every situation. Perhaps setting up a little Monty Carlo thing... It is easy to mess with the program to do things like that know. It is just the free LCC C language compiler:


In general, I think having the gate resistor at 50 ohms is fine for most stuff. 100 ohms might be a little too slow and the primary current might get sort of high through the SIDACs.

There are more scope pics at:


if you like scope pics ;-)