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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I have some of these IGBT's STGW30NC60WD (200Amp pulsed), they have fast <50ns rise and fall times but what concerns me most is the turn-off delay time which is over 100ns.
Would these be suitable in a SSTC? I've never seen a sstc with IGBTs and I wonder if there is a good reason for it. What is interesting to me is the gate capacitance which is about 2-3x times less than in a similarly rated MOSFET, which allows for more efficient gate drive.
I know these would be good for a DRSSTC but I don't have the knowledge/materials/money/patience to build it.
So would these work for a medium size (~300-500khz) SSTC?
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
I did some experiments with early generation STGW30NB60WD IGBTs at 350kHz in a SSTC about 6 years ago and they experienced a lot of heating when running CW at only a kw or so.
Modern IGBTs with minority carrier lifetime control are much faster and can be used in CW SSTCs but they should be tuned in a different way to how you tune a SSTC with MOSFETs. The most favourable operating condition for a MOSFET bridge is a slightly inductive load so that the load current lags the applied voltage. This gives ZVS, prevents turn-on losses due to Cds and also prevents forced reverse recovery of the MOSFET's slow body diodes. All of this is achieved by tuning the inverter to a frequency slightly higher than the resonant frequency of the Tesla Coil - The MOSFET inverter has a long and happy life when operated like this.
For IGBTs the situation is turned on its head. IGBTs have either internal or external fast diodes and much smaller device capacitances, but they don't like interrupting high currents and experience tail current losses. For an IGBT bridge driving a resonant network the most favourable operating condition is with a slightly capacitive load so that the load current leads the applied voltage slightly. This causes the load current to change direction just before each IGBT is told to switch off. It means that current through the IGBT channel naturally falls to zero and commutates smoothly to the diode with no tail current before the IGBT gate drive is actually removed. The downside is that free-wheel diodes see forced reverse recovery but fast diodes used here are well suited to this compared to slow MOSFET body-drain diodes. All this is achieved by operating the inverter at a frequency below the resonant frequency of the Tesla Coil, as is often done with CT feedback from the inverter output current.
Hopefully this will clarify some of the advantages and disadvantages of these two semiconductor technologies for SSTCs.
-Richie,
BTW Jan, I like your Trance tune - you can probably tell from my Avatar I'm also into electronic music.
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SSTC with IGBT's?
