This is a SIDAC IGBT Spark Gap (SISG) module. SIDAC’s are used here as the triggers for IGBT’s to simulate a DC spark gap developed by Terry Fritz here.
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Each driver fires at 900 V to be within the IGBT 1200 V rating. It is a 2 terminal polarised device and multiple drivers are simply daisy chained to reach the desired firing voltage eg 12 kV NST requires 16 stages which adds to cost. However it does open the way for using lower voltages in the 2 kV MOT range where real spark gaps don’t work well. Terry has reached 30 inch sparks with these and Mark has reached 40 inches.
Here is underneath of my SIDAC IGBT driver and the schematic. No I don’t have a PCB and yes some of those components are vertical. I have built it on part of a multi kV strip of SIDAC’s that I have cut off.
Nevertheless the fast components have very short paths and should have low inductance and reasonable current rating. The IGBT fits nicely into a terminal block to allow changing IGBT’s as I want to try some big IGBT’s later. The heatsink was chosen for it’s extra holes rather than need for size. An extra aluminium plate allows the IGBT to be secured.
The black wire allows selection of the number of SIDAC’s to use.
This shows a very rough setup with (almost) 2 turns on the primary and an SISG running at 900 V with 120 nF resulting in a 1 inch spark. Works great on higher inductance coils though such as ignition coils.
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Photo Date: July 21, 2006