fast risetime hv circuit

Search on 'Blumlein pulse generator', is the only idea that occurs to me.

Spark gap! Or exotic avalanche semiconductors, much more work.

John

It's often done with a large stack of transistors that are avalanched. I can't find the link but there was a Dutch group that needed a pulse of over a kilovolt and they used a stash of about 20 transistors. AFAIR those were the old BC107 transistors.

Hi,

Zetex has some devices intended for avalanche use to produce high- voltage pulses. They also have an application note at:

kevin

Great link. Figure 13 shows how it's done. For sub-nsec pulse widths coax stubs are often used.

Have seen any information about sharpening the risetime of sparkgaps? Miike

There's a huge amount of literature on generating very fast HV pulses from spark gaps, avalanche semiconductors, laser-triggered switches, and even mechanical contacts.

What do you really need, in terms of voltage, risetime, pulse width, load, rep-rate? What's the application?

John

Seems a bit old but figure 13 shows how it's done. You can achieve sub-nsec transitions with proper layout and other transistors.

The Zetex parts are very repeatable, trigger beautifully, and slam on to nearly zero voltage drop when they fire. But they tend to be slow. I've not seen them get down to 1 ns risetime.

They would be good for driving a shock line or a Grekhov avalanche diode to speed up the edges.

Some interesting stuff and links:

McEwan did a fair amount of stuff on using common diodes to make fast HV edges. Some of his papers are public.

John

Yes, the challenge in this case will be to find a transistor that avalanches fast enough and also has a sufficiently long lifetime in that mode. I guess the guys at Photonicstech have, and then probably carefully dremeled away the lettering on them ;-)

Thanks! Great link.

I've finally found the Dutch paper again. They used the BC107 which is sluggish but then again this was in 1978 when everone was tooling around in VW-buses with peace stickers and flower vases:

The problem with stacking transistors like this is inductance.

The Zetex parts are made in Russia, possibly on an older fab line. My limited testing indicates that older diffused transistors avalanche usefully, but newer epitaxial ones don't.

John

Hey, here's a spark gap!

I've seen IGBTs driving saturating magnetics to get close to these speeds, in MOPA eximer lasers used in ic fab.

John

The 2n2369 avalanches nicely, in under 300ps. Of course, it's ancient..

Jeroen Belleman

It sure ain't ancient. Digikey has over 20000 of the Fairchild PN2369 in stock and they wouldn't do that if there was no demand. Of course it can't take any voltage to write home about so you'd need a boatload. OTOH they cost less than $0.03 in large quantities.

Then there are tons of STO23 versions such as ZUMT2369, PMBT2369, MMBT2369. Tens of thousands in stock at Digikey, and cheap.

I don't know about that. *Useful* range no, but as far as avalanche, they go at like, 80V.

Tim

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

I bet a gotcha that all the sot parts don't avalanche worth snot.

Whyzat? They're probably the same silicon.

John

Use a krytron or thyratron? Not sure about getting down to low hundreds of picosecond rise times, though. I worked with a lot of those, as well as funky SF6 Marx generator spark gaps several decades back, but I can't really recall specific risetimes - I was in the making the equipment work end of things, not the collecting and analyzing data end of things.

Not a bad read for 11.5 years ago:

...just whip out your high intensity laser and shoot a pulse into the spark gap - you can probably cobble that up over your lunch hour, eh?