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fast risetime hv circuit

J

Joerg

Jan 1, 1970
0
amdx said:
I'm looking for a circuit that will give me risetimes similar to this,
or even two or three times longer. Any ideas?

http://www.photonicstech.com/hv_generators.htm

Thanks, Mike

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.
 
A

amdx

Jan 1, 1970
0
John Larkin said:
Spark gap! Or exotic avalanche semiconductors, much more work.

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

John Larkin

Jan 1, 1970
0
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
 
J

John Larkin

Jan 1, 1970
0
http://www.zetex.com/3.0/appnotes/apps/an8.pdf

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:

http://margo.student.utwente.nl/el/componen/diodefaq.html


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

John
 
J

Joerg

Jan 1, 1970
0
John said:
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.

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 ;-)

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

Some interesting stuff and links:

http://margo.student.utwente.nl/el/componen/diodefaq.html

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

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:
http://msc.eldoc.ub.rug.nl/FILES/root/WiersmaDA/1978/OptCommdeBree/1978OptCommdeBree.pdf
 
J

John Larkin

Jan 1, 1970
0
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:
http://msc.eldoc.ub.rug.nl/FILES/root/WiersmaDA/1978/OptCommdeBree/1978OptCommdeBree.pdf


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
 
A

amdx

Jan 1, 1970
0
John Larkin said:
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
10kv, Risetime? not sure yet but sub nanosecond. Working on drive for a
TEA laser.
Mike
 
J

Joerg

Jan 1, 1970
0
Jeroen said:
The 2n2369 avalanches nicely, in under 300ps. Of course, it's ancient..

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.
 
T

Tim Williams

Jan 1, 1970
0
Joerg said:
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.

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

2N3904s avalanche, too -- I have a batch of Fairchilds that go off in the
110V range, with less than a couple nanosecond rise time (probably limited
by my scope's bandwidth).

Tim
 
J

JosephKK

Jan 1, 1970
0
Joerg said:
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 bet a gotcha that all the sot parts don't avalanche worth snot.
 
E

Ecnerwal

Jan 1, 1970
0
amdx said:
Have seen any information about sharpening the risetime of sparkgaps?

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:

http://www.electricstuff.co.uk/pulse.html

....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?
 
J

Joerg

Jan 1, 1970
0
Tim said:
I don't know about that. *Useful* range no, but as far as avalanche, they
go at like, 80V.

Wow, I didn't know they avalanched this high. Cool.

2N3904s avalanche, too -- I have a batch of Fairchilds that go off in the
110V range, with less than a couple nanosecond rise time (probably limited
by my scope's bandwidth).

You might beat that by using the SOT23 version MMBT3904 and RF-style
trace layout.
 
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