Thyratrons? Alternatives?

[Joerg]

The Phantom wrote:

On Mon, 05 May 2008 13:40:11 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Hey guys,

Seems like thyratrons have become quite rare these days and SCRs or GTOs
are just too freaking slow. Is there a readily available alternative
that doesn't cost an arm and a leg, meaning under $100? A kilovolt would
be nice and >50A.

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

It doesn't really matter. 5-10V would be fine. The less the better, not
because of function but because of dissipation.

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

It must be able to turn on within 100nsec and retriggerable after a
couple usec or so.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
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[Joerg]

Frithiof Andreas Jensen wrote:

"Joerg" <notthisjoergsch@removethispacbell.net> skrev i en meddelelse
news:NgKTj.8556$iK6.2263@nlpi069.nbdc.sbc.com...
Hey guys,

Seems like thyratrons have become quite rare these days and SCRs or GTOs
are just too freaking slow. Is there a readily available alternative that
doesn't cost an arm and a leg, meaning under $100? A kilovolt would be
nice and >50A.

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.

I'll have to check that idea, thanks. The current diversion could be an
issue. It'll be tens of amps.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

 

[JosephKK]

On Mon, 05 May 2008 16:45:33 -0700, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

John Larkin wrote:
On Mon, 05 May 2008 13:40:11 -0700, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Hey guys,

Seems like thyratrons have become quite rare these days and SCRs or GTOs
are just too freaking slow. Is there a readily available alternative
that doesn't cost an arm and a leg, meaning under $100? A kilovolt would
be nice and >50A.

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.


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.


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.


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.

In that case maybe what you want is a spark gap or a field emission
device.

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.

http://www.highlandtechnology.com/DSS/T220DS.html

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


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?