Made a test circuit to measure IGBT turn-off characteristics at relatively high current as is needed for phase-shift QCW use.  Made with copper foil on both sides of 1mm plastic (polycarbonate) to minimize interconnect inductance.  IGBT leads are held against copper with a spring clamp and rubber pad to allow for replacing parts.  Thermocouple taped and clamped to IGBT top, also clamping IGBT to a small piece of aluminum sheet metal to simulate heat sink.  Having that heat sink metal adjacent and parallel to circuit board helps reduce inductance.  IGBT body is against edge of circuit board (foil/plastic) for almost zero (<1mm) external lead length.  Still some lead length inside package epoxy.  This testing is at 320Vbus, switching from 140A to 0A.

Schematic:



Picture with spring clamp holding IGBT leads.  Only connection between left emitter lead carrying 140A and right emitter lead for gate drive is inside IGBT package.  Isolated on board.  Gate drive is from GDT through buffer, so circuitry is isolated too.



Spring clamp removed for visibility:



Even with all the measures to minimize parasitic inductance, voltage spikes are high.  These are fast IGBTs, chosen intentionally for phase-shift QCW, to minimize turn-off energy.  First scope plot (left image) shows Vge with ~12ns fall time and Vee (voltage from one emitter lead to the other).  Emitter spike is ~55V and around 12ns wide, indicating roughly 12ns current fall time.  Shows value of Kelvin connection (of not adding that 55V signal to internal gate voltage).  Also shows how spike exists just across internal-package lead inductance.  Right plot shows Vce, measured on board foil and again on IGBT package back-side (on heat sink aluminum).  About 50V difference.  Combined emitter and collector spikes add 105V to internal IGBT Vce due to just inductance of leads inside package.
Red is Vge and blue is Vee on left plot.  Green is measuring current.  Ignore that one for turn-off.  Inductance in current-sense resistors causes large spike compared to the 28V drop at 140A.  Right plot, red is Vce measured on IGBT package back (heat sink).  Blue is Vce measured on board foil.



Next scope plot shows Vge with ~12ns fall time, and again at ~30ns fall time in the hopes that current fall time might increase a bit.  Delays Vce spike (measured on foil), but doesn't reduce amplitude significantly:



Tried 50ns Vge fall time.  Still no reduction in spikes.  Current fall is enough delayed from Vge fall that Vge timing doesn't seem to matter.



Tried even slower, 120ns Vge fall time.  Still same spike amplitude.  (Horizontal scale is now 25ns/div, so spike looks narrower.  Really about the same.)  Blue is Vge.  Red is Vce measured on board foil.



Fast switching is good for low Eoff.  Was hoping to slow it slightly.  Looks like I'll need some R+C snubbers instead to keep Vce below 650V specification.  BTW, I fried first test part testing at 200A before realizing how high spikes were.  Even at 140A, considering combined emitter and collector spikes, peak voltage is about 700V, so slightly above spec limit.  LTSpice simulations appear to show R+C snubbing will be effective.  Adds significant power dissipation.  However, at least that power is in resistors, so not adding to thermal stress of IGBT die.

Yes. Even at these low powers the boro does get hot quickly. If I could see any use for this little trick I'd search out some quartz but...

I build up a little ramped DRSSTC coil using labcoats circuit board. It made things super easy and the resulting coil is very fun. ~300kHz operating.
I was measuring the length of the sparks using a piece of glass tubing and got the silly idea of putting the glass tubing over the breakout.

Instant perfect sword sparks. And a funny hollow blowing down a glass tube noise.

I hadn't seen any other idiot try this so here you go. I'm the idiot in this case...

https://www.flickr.com/photos/8763834@N02/52958940125/in/dateposted/

The sparks are about 15 inches. No real tuning yet except for calculations. Running at ~5mS and 200 volts.

Cheers.

Well, I am back on this forum again after several years...

Anyways, I found the guts of this Spellman high voltage power supply in the garbage, and it seems like everything should work. All the power components test fine with a multimeter. The only problem is that the front panel (with all the controls) is missing and someone took all the screws holding the power components together.

Does anyone have any ideas on how to get it working again? There seems to be some interface on the back for connecting to a computer. I might have to just bite the bullet and design my own controller. From looking at their manuals it seems like something similar to an SLR inverter is used.

What is hypervoice?