On Sun, 18 Dec 2005 21:33:52 +0100, Rolf_B
wrote:

John Larkin wrote:

A 1N4007 can also be used as a drift step-recovery diode and as a
plasma avalanche diode. Together, two can generate a kilovolt edge
with a 100 ps risetime.

Very interesting. The 1N4007 seem to be very versatile devices.
They are available with a SOD-57 glass envelope, too (1N4007G?).
These are fairly well photoconductive. When illuminated by
a high efficiency IR LED (HSDL-4230 or so) current transfer
ratios of 0.001 can be achieved. Not too much, but with
two LEDs 100uA of photocurrent is obtainable. This is OK for
a pass element in an "electrostatic" power supply for e.g.
electron or ion lens systems.

A high-voltage optocoupler; cool.

I've posted a schematic for a hv opamp (400 v p-p) that uses two
optoisolators as the output push-pull stage... it's very cheap and
simple. A higher-voltage photodetector, like a glass power diode,
sounds useful, too.

I worked once with a company in Southern California that had a neat
gadget: it was a truncated cone of silicon with gold contacts on the
base and the flattened apex. It would stand off something like 5KV
until you whacked it from above with a laser, illuminating all the
sides of the cone, whence it would conduct hard. I think they went out
of business, though; it was pretty obscure.

John