fast high-voltage diodes

It's interesting that nearly all "fast recovery" HV diodes spec Trr at

50 ns. That goes for single-junction 1KV diodes and higher-voltage stacks. And the 50 ns is either specified as typ or as max.

I guess there's some physics there, the carrier drift time across a kilovolt of "i" region or something.

I guess I'll have to make my own, a string of lots of lower-voltage diodes. There are duals and triples and even a few quads in surface-mount packages. But almost all of the 200-300 volt diodes also spec Trr at 50 ns!

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John Larkin         Highland Technology, Inc 

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John Larkin
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They're in series so only one has to turn off to meet the 50 ns time.

I wonder what that does to the rest of the stack?

Reply to
Tom Miller

The first one that recovers will avalanche as most of the reverse voltage tries to straddle it. That might be OK if the power dissipation doesn't fry it.

I suppose I could test them, and include a thermal imaging step to make sure that some diodes in the string aren't getting too hot. Nuisance.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

most of the HV recitifer stacks I've come across are either

1) strings of carefully matched diodes. Replace everything if there's a failure.

2) compensated with resistors, caps or MOVs, but this is for higher applications

3) strings of avalanch rated diodes (easiest of all 3)

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Reply to
Cydrome Leader

It gets worse with 200V Schottky diodes like we had in a thread a while ago. Often they spec no carrier lifetime. A new kid that doesn't know might assume Schottky is always infinitely fast and ... phsssss ... *PHUT*

Then they call the fast, ultra-fast, hyper-fast an so on. Like in Spain, where a hole in the wall grocery was called supermercado and a store the size of an average Trader Joe's was called hypermercado. Couldn't believe it.

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Reply to
Joerg

Yeah, like this:

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The next category should be ACTUALLY FAST.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

Den torsdag den 21. august 2014 19.05.41 UTC+2 skrev John Larkin:

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-Lasse

Reply to
Lasse Langwadt Christensen

A friend from church once had a car that was labeled "super-ultra low emission vehicle". Maybe something like that would work :-)

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Reply to
Joerg

I have one of those. One of these days I will get it running.

Regards, tm

Reply to
Tom Miller

A car up on blocks is nearly a zero-pollution vehicle.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

Yep, Typical string of fast diodes. What recovery time are you looking for?

Cheers

Reply to
Martin Riddle

Trr=30ns @25c

Cheers

Reply to
Martin Riddle

Interesting, thanks, but I need smaller, lower current things, 25 mA sort of range. Maybe I could put a string of surface-mount duals/triples/quads on a baby board, make my own sip package.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

10 ns or less would be nice. It's a shame to pump kilovolts into a capacitor and immediately take some of it back.

Interesting data sheet. There are two series that differ only in (max? typ?) Trr. Then there's a typ Trr graph that doesn't specify which series it applies to. At 75C, we're back to.... 50 ns!

I guess we'll have to buy a lot of diodes and test them.

Where are the Data Sheet Police when you need them?

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

You could try DeanTechnology too. I only see 35ns but you should call and see if they have anything.

Cheers

Reply to
Martin Riddle

sure, we use ~320 200v diodes for a 50kv string. You still need all the small caps and R's , etc.

Jamie

Reply to
Maynard A. Philbrook Jr.

Thanks. Their RSUF6 (formerly HVCA?) specs 35 ns max, which is about the best thing around.

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

HVCA is part of Dean. I think Dean grew out of Collimer Semi and started buying small HV related companies. They've been around some time.

Cheers

Reply to
Martin Riddle

Unless you can convince someone to make SiC schottky in a 25mA size, you're SOL.

Well, almost; you might find some of these laying around yet. As a small quantity company, it's not actually a bit cut into your manufacturability:

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Technically, you still have the reverse recovery of space charge, but gee, it's just whatever's floating in a vacuum, not soaked into a semiconductor junction. Frequency response is limited by geometry, which will be better on dampers than the HV types with those bell shaped anodes.

There may be smaller ones out there, this is the first smallest in this class (damper) I've seen. Older ones like 2X2A are a bit too weak (andb bulky) though.

Tim

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Reply to
Tim Williams

There were those tiny pencil tube rectifiers that Tektronix soldered into their CRT HV supplies. One of those would not be totally absurd to use on a modern PCB. Likely not good for 25 mA.

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Reply to
John Larkin

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