I guess a stack of 600V silicon carbide diodes would work well as they can have less reverse recovery losses? I guess its pretty easy to make a diode stack, just series diodes on a PCB (optionally in oil).
cheers, Jamie
when do that, you should be bridging the string of each diode with a high value R and small cap, otherwise, the recovery time error could force you to pay the price.
Jamie
Schottky diodes don't have recovery, but they DO have highly nonlinear capacitance, which behaves much the same way. Don't forget the caps!
It's too bad they don't make any 0.5 or 1A SiC schottky diodes in DO- cases. I'd love them for this sort of use. Cree and Infineon only make TO-220 and related packages, go figure.
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
ferrite
inductance
thinking
also
Inc.
Ithem.
and
Von.
Rats. You beat me to it. X-ray tube power supplies was worrying my mind as an alternate way to find a supply. Almost onto the X-ray issues of E-beam welding.
?-]
Schottky diodes are nice due to their low Vf, they seem to be kind of hard to get in large Vrb these days. I did recently see some article on schottky up in the 1200..1500 volt range but I do not know who is making them atm..
Which brings up another subject. We have at our facility the first x-linking Irradiation machine, still in operation, ever made! Yes, it's old and still has most of its original style electronics. We are in the process of making it into a capital project and updating it and one of the ideas is to maybe try out a schottky electron emitter instead of the tungsten.
Should be interesting to see what chances will be needed to the beam section.
Jamie
Hi,
thin lead sheet can block 99.9%+ of 50kV and lower x-rays afaik!
cheers, Jamie
Pretty much Cree and Infineon, and I read something about Dow and a couple others growing the SiC wafers (raw material, not the finished chips).
Note that schottky diodes suffer increased losses when constructed for higher breakdown. A 40V diode might drop 0.7V at rated current, while an
80V diode might drop 0.9V. A comparable (100V) junction diode might drop 1.0V, so the conduction savings is modest. "Super barrier" schottkies go up to 300V, using some interesting MOS structures to improve breakdown; these structures increase the voltage drop further, so that a 300V schottky has essentially identical conduction losses to a 400V junction diode.Anything beyond there (600V, 1200V and more) is SiC at this time. As far as I know, these are fabricated pretty much like a 40V Si schottky, but with accordingly higher bandgap and breakdown, the voltage drop is much higher. Resistivity is particularly high, so much so that a SiC schottky looks worse than a high speed junction diode in most uses (Vf ~ 2V at rated current, IIRC).
The main advantages to schottky are for rectification under 20V, and high frequency (over 500kHz or so), where recovery losses dominate.
When evaluating a design, also keep in mind that schottkies have tremendously higher capacitance. A low voltage (50-200V), high speed junction diode can recover faster (~50ns) than a schottky takes to recharge (could be >100ns at < half rated current); this, as well as the strong nonlinearity, can actually worsen performance.
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
=20
=20
make=20
Not normal schottky diodes then, maybe SiC versions or not schottky at all.
Wow, that should be a museum piece instead.
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