[TCML] SISG heating at high freqencies
bartb at classictesla.com
Thu Apr 17 19:10:40 MDT 2008
Sounds like the SIDAC's are not turning off, but rather sharing the
current path even after the IGBT turns on. Did you make any
modifications to the circuit such as the anti-parallel diodes? Were all
4 segments of SIDAC's scorching hot or just on the segment with the that
particular hot IGBT?
Peter Terren wrote:
> I was playing with a 4 segment SISG with a 4 inch coil about 8 inches
> tall and 0.06 uF cap.
> Primary of 2 turns from a ballasted MOT (half wave rectified) and no
> toroid. Frequency would have been quite high >2-300kHz or even more.
> I was just messing around with the threshold voltages for curiosity
> and was using 3 of the 4 segments to get 1 inch sparks.
> I was quite surprised to find that the SIDAC's were scorching hot and
> the IGBT's were uncomfortably hot, particularly one of them after a
> very short run. Considering that these have been used by others on a
> pole pig with only mild heating, that surprised me.
> It sounds like they had some frequency dependent problem because the
> SISG works OK (ie cold) with more primary inductance/capacitance.
> Beats me why the SIDAC's were getting hot though. Perhaps the IGBT's
> weren't turning on fast or fully so the SIDAC's spend more of the time
> conducting throughout the cycle relatively. Perhaps a lower gate
> resistor may have helped (I was using 100 ohms).
> I was planning to use a smaller 4 stage SISG for a demo mini coil but
> would have to sort out the frequency issues first.
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