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Using avalanche rectifiers in series for higher voltages - equalizing resistors?
cvanc:
Hi all-
Is it a valid general statement that avalanche rectifiers used in series for higher voltage do NOT need equalizing resistors? I haven't used them before in this way and I want to verify.
I'm thinking of using some version of BY228 for my project, but really it's a question about avalanche rectifiers in general. Thanks for any clarity you can provide.
Example datasheet attached.
MagicSmoker:
Technically correct, but not the best practice, really. The main advantage of avalanche rectifiers is that they don't need protection from transients (up to their max energy rating, anyway). The same mechanism of controlled avalanche enables them to self-equalize when wired in series, but that requires one or more diodes operating near their breakdown knee resulting in greater power dissipation. So, it's still a good idea to use static equalization (ie - a parallel resistor across each diode), but there is no need for dynamic equalization (ie - a parallel RC across each diode).
HighVoltage:
Depending on your project but in general it will work without any problems.
I have used the Vishay BYT62 diodes in such a way and it worked well for 3 of them in series.
David Hess:
--- Quote from: cvanc on January 03, 2020, 05:32:10 pm ---Is it a valid general statement that avalanche rectifiers used in series for higher voltage do NOT need equalizing resistors? I haven't used them before in this way and I want to verify.
--- End quote ---
What makes avalanche rectifiers different is that they are fabricated to have a very uniform junction so the entire junction breaks down at the same time instead of just selected spots which could lead to localized overheating and damage. So they can be reliably used in series without balancing but as MagicSmoker points out, thermal constraints still need to be considered. There is probably some derating rule for operating them this way but offhand I do not know it.
cvanc:
Thank you all, it's much appreciated.
OK so it should be possible to do this without resistors. But I'd like this to be robust under fault conditions so let's talk about the correct resistor value, I will probably add them.
Is 1 Meg a reasonable guess? Is there a way to calculate the optimum value? I took a quick look and didn't find much.
(Of course the voltage rating of the resistors needs to be adequate; I'm thinking Vishay VR25 or VR37. Datasheet attached.)
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