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Why are 900V semiconductors not common? When 1200 are.
Miyuki:
Hi. Just little thought.
Why are almost no semiconductors with a 900V rating?
It might be my Eurocentric view where 400V AC mains is industry standard.
But it looks wastefully to me to use 1200V rated ones on 600V DC
With SiC it is not a huge issue, but all Si parts have way worse parameters, IGBTs and Diodes are slow, MOSFETS tend to have variants about that voltage because 1200V is unreachable for them
600V rating makes clear sense, it is nice for 230V AC mains
But why they came with 1200V? Other than it is double the 600V.
Because then 1700V is also relatively common and not directly to 2400V.
PartialDischarge:
This paper explains why you need a 1200V rated semiconductor for a 400vac line and so on.
https://library.e.abb.com/public/6f03cdd0f2264ff48f2992e62497dd5a/Voltage%20ratings%20of%20high%20power%20_%205SYA%202051NLay.pdf
To give you another data point, for a 6.6kVrms line, a standard medium voltage distribution voltage, semiconductors, stacked, that can handle up to 20kVpk are needed
Alti:
--- Quote from: Miyuki on September 22, 2021, 11:27:47 am ---600V rating makes clear sense, it is nice for 230V AC mains
--- End quote ---
For 230VAC and 600V rated semiconductors won't last too long. It is close to impossible to limit mains incoming voltage to 600V during 8us/20us surge test. The least stringent surge test is 1500V via 2R (category I installation) IIRC. You could filter 230VAC low pass RLC and make a ~400VDC, then 600V semiconductors (transistors) should suffice under some conditions, but not directly at AC mains.
I am writing this just to make sure people are not putting 600V mosfets at 230VAC mains.
T3sl4co1l:
I've seen plenty of 500 and 550V MOSFETs in 240V products...
Note that most things use a big chunky capacitor before or at the MOSFETs, absorbing the surge. This does depend on the value, and relative to other things like the CMC's leakage and resistance, and NTC if applicable (which can be helpful in smaller converters, but is too little resistance to help much over say 100W, but capacitance might not be enough until 500W+).
900V Si MOSFETs are common enough, perhaps more common back in the day because conventional VDMOS had specific Rds(on) going as Vds^2 -- so the performance at 900V was already about half that of an equivalent geometry 600V part, and half again at 1200V, making the latter particularly unfavorable. I spec'd such a part back in 2011 or so, for exactly that reason. SuperJunction types have quickly taken over since then (they were already rising at that time, alas just not available in the size and voltage needed for that project), and offer linear performance at all ratings -- that is, constant switching area (Id * Vds) per die area, no nasty quadratic penalty. So higher voltage devices aren't unusually poor, and 600-700V and 1200V parts are very common now.
And we have SiC now too, with an even more aggressive performance curve (the dies are TEENY!). I forget if they're doing SJ in them now, but even without, they offer great performance at 1200V and up. At 600 and 900V, you might simply not need the performance edge and Si is fine; or at 600V and below, power GaN is available if you need even higher performance.
Tim
Alti:
Typically thyristors and triacs intended for 230VAC applications have 900V rated Vdsm/Vrsm (non-repetitive). For example popular BTA16-800 from ST.
Unless some serious RLC is capable of attenuating surges, but that is limited to low-ish powers to be practical.
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