Thyratrons? Alternatives?

IGBT? IIRC, 1-1.5kV is available. Best regards, Spehro Pefhany

A thyratron is a switch as I recall. How about two or three cascaded FETs ? The circuit is called Marx stack I believe and achieves few ns out of ordinary FETs by avalanching them. 50 Amps are hefty though.

Rene

How slow is "too freaking"? The Russians still make some nice hydrogen thyratrons; Los Alamos used to buy them on the sly, maybe still do.

You can get 1KV from one or two mosfets, tens of amps in a few ns. A string of maybe 3 avalanche transistors, like the Zetex SOT-23's, will output 30 amps or so at 1KV, for short pulses.

I did one gadget that puts 1200 volt pulses into 50 ohms, 2400 volts into a small capacitive load, with 3 ns pulse width, at up to 500 KHz. It uses a drift step-recovery diode (another Russian invention) driven by a couple of 400 volt mosfets.

It was fun, but we didn't sell many.

John

Those are great but even the "HiperFast" are still >250nsec turn-off time. However, I'll go through the latest offerings again. Thanks.

Supertex has one that can do this current but the problem would be the lifetime. I believe they quoted 4e11 avalanches. That's high but not infinite and I'd blow through a set within days.

I need to switch within 100nsec or so. Do you remember the Russian company? Svetlana or Sovtek? Boutique prices? A thyratron would be cool but it'll have to be something that can still be bought a few years from now.

In my case a FET would work, that's what I am trying right now. But it ain't ideal because it should turn off when a certain resonance has run its course, not when a gate driver tells it to. In a pinch I can try some nifty feedback for that, and maybe I have to.

Sure looks high-tech but we'd need a good order of magnitude higher PRF. Do you think it can be spiffed up some more?

Beefier than this starts to get slow.

. . .

Aha! Thanks, John. They even sell a RoHS version which is encouraging.

Well, pretty much. Can't reveal details though.

Thanks, Jeff. If I decide to go the FET route those look like good candidates. 100A pulse sound just like the ticket.

How about:

Don't know what the prices run (damned priceless websites), but Perkin Elmer claims they still make them, and the baby of the bunch (HY-2) would exceed your ratings. The one source one distributor setup probably won't sit well with you, and the price may not be low enough either.

I used to use something similar to the HY-3192 on Nitrogen lasers, but I think it was an EG&G part. Suppose it's possible one bought the other in the couple of decades I haven't been doing that.

Google spits up two websites from China, not my idea of a good source, especially if your hush-hush application is in your typical medical field.

And a thyratron won't be cheap. 1000 volt fets and transistors are cheap. At 100 ns, I'd thik that a horizontal output transistor might work.

The Zetex avalanche things would certainly turn off, a lot like an scr or a tyratron.

PRF of 5 MHz? That excludes most devices, including thyratrons.

John

How much forward drop can you tolerate while it's on?

What kind of pulse, magnitude and duration will trigger it on?

"Joerg" skrev i en meddelelse news:NgKTj.8556$ snipped-for-privacy@nlpi069.nbdc.sbc.com...

How about a Cascode with a high-voltage bipolar transistor "on top" and a low-voltage MOSFET driving the Emitter of the bipolar?

Just remember that while the Bipolar storage time runs, the full collector current is diverted to the Base so you have to have somewhere to put the charge. After storage time the whole contraption blocks in about 10-20 ns so, again, there will be transients. The MOSFET only need to be able to hold the maximum B-E voltage so it will be cheap and efficient; the Bipolar does not have to be particularly fast and since the Emitter is cut at turnoff it's SOA becomes square, right to the VCEmax limit.

Hope that helps.

Somehow I don't think you'll manage to run a thyratron at 1.5MHz, Joerg. Check your numbers...!?

(Conservative estimate, 4e11 / (7 days = 0.6M seconds) = 1.5MHz.)

Tim

-- Deep Fryer: A very philosophical monk. Website @

There are other permutations of those but the problem is that many are (most likely) still under export restriction so you can't use them in designs that are to be sold worldwide.

Not that high but this one can't contain such "disposable" parts. :-(