You mean for the snubber? I've already got:
Hmm, offhand I'm not seeing anything of interest.
Tim
-- Deep Fryer: A very philosophical monk. Website @
...
Yes. You were talking about 10A RMS / 0.1uF / 1000VDC for the snubber. The items at electronicsurplus are several times that capacitance which (from what little I know about snubbers) is ok. My thought is that physically-larger caps like these will hold up better. (However, I don't know what ringing frequency you need to suppress, hence whether they will be in spec.)
-jiw
Well, big capacitance eats into dV/dt. I need to slow dV/dt, because big dV/dt apparently blows transistors and sprays gangbusters RFI. But I can't slow it too far, I need a minimum of, oh, let's say 150V/us to get a reasonable squarewave at 20kHz. 300V/us is pretty good up to 50kHz, which is the highest frequency I want to cover. So I really can't afford much capacitance, and that concerns me because all the beefy capacitors (like the Cornell Dubilier 935's Mouser and Allied sell) seem to be 1uF or more.
One of those big bastards, like I think it was on the Nebraska site I saw an IGBT snubber capacitor module, made to bolt directly onto buss bars- rated something like 1200V and 40uF. That's going to be perfect for like, traction control IGBTs, or something relatively slow like that. Probably a good couple hundred amps, and switching under 1kHz. Hundreds of kVA, a little out of my scope -- although if I were building an induction heater that size, it would go about that frequency.
Tim
-- Deep Fryer: A very philosophical monk. Website @
At the power levels you are using i hope that you did nor forget an ohm or so of series resistance.
On the snubber capacitor? I tried one initially (0.47 ohm), but it wasn't rated for enough power and started stinking. ;-) That was at 100V. I don't have any resistors small enough in value, low inductance and large enough in power to serve.
Without a resistor seems to work okay (at least after the first half cycle), why?
Tim
-- Deep Fryer: A very philosophical monk. Website @
Hmmm. Do you know / can you measure the ESR and ESL of the capacitor.
Specs:
Sounds like you are on a better track now. I might have been late to the game, but maybe i asked you a worthwhile question.
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