audio recording on IC -help wanted

[Joerg]

Lostgallifreyan wrote:

George Herold <ggherold@gmail.com> wrote in news:379c1689-21a2-456e-9d3b-
bf5874b7feb6@2g2000prl.googlegroups.com:

I love laser diode's.. K. Libbrecht and Jan Hall's RSI article circa
'93? is the classic current robbing circuit. I'd been trying to
modulate a LD current driver at high speed. I read the abstract to
the above article and said.. "no way". Then I read it and learned
something.


Here's something to consider: I think many posts here are assuming a
switching modulator wheras I am after a continuously proportional and DC
coupled type. I can hybridise with a PWM control, and eventually will go to
that, probably, but for now, what do you do if you want linear control? Never
mind that diode light output isn't at all linear, we might as well start with
what we CAN control... So do we really use a Darlington? I understand that
those are made to switch fast, they're not chosen for a long linear operating
region... So that leaves some fast single stage transistor, and a sense
resistor, and a controller, likely an op-amp.....


Is this getting through? The LM317 in data sheet approved constant
current mode IS just that, though not a shunt mod. But it does the opamp, the
sense resistor, and the hefty transistor to drive up to 1.5A. It's not as
daft as it looks, and it performs better than anyone ever told me it could.

Risque if you want to do 500kHz as you mentioned in another post.

Anyway, assuming I do shunt part of a constant current from the diode, what
might be the simplest way to do it? As far as I know, something like Robin
Bowden's 'Die4drive' circuit might have a basis for this with its MOSFET,
opamp amd sense resistor, but that's not a shunt mod either...

In a DC application (well, sort of, low kHz stuff) I did it the same way
as fast applications: A top current source that makes sure the DC
current never ever goes above xxx milliamps. Can be built around a LM317
if you wish. Then an opamp-controlled current sink from the LD anode to
ground (the LD cathode is also on ground). This current sink then
"wastes" x amount of the current from the upper source by sinking it
into ground, depending on the control signal on the IN+ of the opamp.
What you control is in essence how much of the top source current goes
through the LD and how much is wasted.

The super-prudent approach is a high voltage and resistors. The sum of
the resistors makes sure the LD can never get too much current. Then
current-rob like above. Resistors can't go unstable on you

Getting back to the topic, whatever we do, it would REALLY help if we all had
access to some reasonable semblance (electrically) of a single mode laser
diode in spice. It's long overdue. It would save students and schools and
hobbyists a lot of money if it was there. Linear Technology have given us
LTspice to use for free, now we need things like this to put it to use.

Don't hold your breath. For many people (like me) a LD model would only
make sense if the optical side is in it as well and that makes one heck
of a complicated model. Otherwise it isn't terribly useful.

In other news, I seem to have dropped alt.lasers from the cross-post list.
Annoying.

I think that's ok. Those guys know all this stuff I suppose.

--
Regards, Joerg

http://www.analogconsultants.com/

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

 

[Joel Koltner]

That's a great explanation (and I appreciate the connection to LDOs) Phil;
thanks!

I suppose that purposely adding resistance in series between the output of the
LM317 (emitter of its drive transistor) and whatever it is you're trying to
(current) regulate ought to help, but that's considered a rather ugly hack
when it's no harder to do it the "right" way?

---Joel

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7dduinF2bpdd5U1@mid.individual.net:

You can build a current drive out of a LM317, I've even used it as an AM
modulator. But 500kHz, nope, it ain't going to go quite that far.

Want to bet? > I grant that it won't go further, I tried the model at 1 MHz
and it degraded to crude sine waves, but 500 KHz is ok. As far as I can tell,
the main weakness seems to be a small range of acceptable capacitance on my
controlling op-amp's feedback loop so parasitic capacitances alone may, or
may NOT, make it work well. And it's very dependent on the diode too which is
why I want an LD model. But when I built my first real circuit for this
design a few months back the LD showed characteristics similar to the 1N4148
model which are much more favourable to damping high frequency ringing than
if it had been a 'hard' diode like a 1N4005 that barely responds with Vf
changes to current changes and forces. I think LD's do vary Vf a lot with
current so they damp the ringing well enough.

But I'll know more when I've ate the pudding.

 

[Lostgallifreyan]

"Tim Williams" <tmoranwms@charter.net> wrote in
news:Ticcm.95224$Qg6.25743@newsfe14.iad:

Can I get a modern definition for "snivets"?

Seconded. All I can think of is that little sniffle that people do when
they're trying to work out whether they've got a cold or not.

 

[Lostgallifreyan]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:qe6dnQAVoMdevOzXnZ2dnUVZ_vBi4p2d@supernews.com:

Lostgallifreyan wrote:
Vladimir Vassilevsky <nospam@nowhere.com> wrote in
news:8_2dnS4nlv14f-3XnZ2dnUVZ_g2dnZ2d@giganews.com:


Lostgallifreyan wrote:

Vladimir Vassilevsky <nospam@nowhere.com> wrote in
news:IMWdnYD_roXLQ- 3XnZ2dnUVZ_rqdnZ2d@giganews.com:


This type of circuit can easily modulate the LD at the rates of up
to several GHz; the limits are set by the RF parasitics.

But what would you do if you were asked to do 'analog' proportional
DC coupled modulations that tracked a continuously varying signal,
instead of high speed switched signalling? And how fast would it go
then?
The LDs are VERY nonlinear (light vs current), so I would use voltage
to frequency conversion, PWM, delta sigma or some other pulse
modulation technique. A lot depends on your requirements, however
tracking at the speed of the 1/10 of the pulse rate ballpark should
not be a big problem.


I like that idea. I've considered it but I think it could be more
complex than the simple modulator based on an LM317. I like the real
visual linearity that could result from very fast PWM though. It's
another idea I want to try once I get this LM317 lark worked out of my
system.

LDs' output powers are pretty linear with bias current once you're above
threshold, so if Class A bias is OK, you're in pretty good shape. You
can run a power feedback loop using the monitor photodiode if you really
need to, but you usually won't.

Good stuff. I thoughyt they were fairly linear too, above threshold (and my
design sets the low peak to just sub-threshold too. They can mode hop though,
which doesn't help, but if they're going to do that they'll do it anyway and
impair the effect of a clean drawn line in graphics.

The PWM idea isn't great for graphics either, but it depends how fast the
main cycle is, if it's possible to modulate on a 10 MHz carrier without
awkward exotic precautions, it isn't going to show up as a dashed line using
any scanner currently available. That makes it an attractive idea for other
types of laser too, and also AOM's too, which is cool because proportional
PCAOM's cost more. (Not that I've even had the money and availaibility of
such to try those).

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7dduinF2bpdd5U1@mid.individual.net:

You can build a current drive out of a LM317, I've even used it as an AM
modulator. But 500kHz, nope, it ain't going to go quite that far.


Want to bet? > I grant that it won't go further, I tried the model at 1 MHz
and it degraded to crude sine waves, but 500 KHz is ok. As far as I can tell,
the main weakness seems to be a small range of acceptable capacitance on my
controlling op-amp's feedback loop so parasitic capacitances alone may, or
may NOT, make it work well. And it's very dependent on the diode too which is
why I want an LD model. But when I built my first real circuit for this
design a few months back the LD showed characteristics similar to the 1N4148
model which are much more favourable to damping high frequency ringing than
if it had been a 'hard' diode like a 1N4005 that barely responds with Vf
changes to current changes and forces. I think LD's do vary Vf a lot with
current so they damp the ringing well enough.

It can work but as Phil had mentioned the LM317's stability becomes iffy
beyond a certain frequency when operated as a current source. It's like
taking a small car past 120mph.

But I'll know more when I've ate the pudding.

Remember, laser diodes die quietly. There is no tchk ... *phut* but
there is that painful hit in the bank account.

--
Regards, Joerg

http://www.analogconsultants.com/

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

 

[Joerg]

Lostgallifreyan wrote:

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:qe6dnQAVoMdevOzXnZ2dnUVZ_vBi4p2d@supernews.com:

Lostgallifreyan wrote:
Vladimir Vassilevsky <nospam@nowhere.com> wrote in
news:8_2dnS4nlv14f-3XnZ2dnUVZ_g2dnZ2d@giganews.com:

Lostgallifreyan wrote:

Vladimir Vassilevsky <nospam@nowhere.com> wrote in
news:IMWdnYD_roXLQ- 3XnZ2dnUVZ_rqdnZ2d@giganews.com:


This type of circuit can easily modulate the LD at the rates of up
to several GHz; the limits are set by the RF parasitics.
But what would you do if you were asked to do 'analog' proportional
DC coupled modulations that tracked a continuously varying signal,
instead of high speed switched signalling? And how fast would it go
then?
The LDs are VERY nonlinear (light vs current), so I would use voltage
to frequency conversion, PWM, delta sigma or some other pulse
modulation technique. A lot depends on your requirements, however
tracking at the speed of the 1/10 of the pulse rate ballpark should
not be a big problem.

I like that idea. I've considered it but I think it could be more
complex than the simple modulator based on an LM317. I like the real
visual linearity that could result from very fast PWM though. It's
another idea I want to try once I get this LM317 lark worked out of my
system.
LDs' output powers are pretty linear with bias current once you're above
threshold, so if Class A bias is OK, you're in pretty good shape. You
can run a power feedback loop using the monitor photodiode if you really
need to, but you usually won't.


Good stuff. I thoughyt they were fairly linear too, above threshold (and my
design sets the low peak to just sub-threshold too. They can mode hop though,
which doesn't help, but if they're going to do that they'll do it anyway and
impair the effect of a clean drawn line in graphics.

The PWM idea isn't great for graphics either, but it depends how fast the
main cycle is, if it's possible to modulate on a 10 MHz carrier without
awkward exotic precautions, it isn't going to show up as a dashed line using
any scanner currently available. That makes it an attractive idea for other
types of laser too, and also AOM's too, which is cool because proportional
PCAOM's cost more. (Not that I've even had the money and availaibility of
such to try those).

10MHz is sluggishly slow for a decent laser diode.

--
Regards, Joerg

http://www.analogconsultants.com/

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

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7ddv8fF2b3uqiU1@mid.individual.net:

Risque if you want to do 500kHz as you mentioned in another post.

I'm all for pushing the envelope, there's no hide at stake here.
It sure looks like it will work. It's 'competing' with systems that can do
100 or 200 KHz at best generally, and none of these devices are needed to go
further. They work alongside laser systems incapable of more that 10 K, often
as not.

The main point is to see what's possible, and to establish the safe operating
area so when I really want to use this thing I can have a very good idea how
to make it right, at more reasonable figures. And I'll know it will draw a
very clean line, which is what the people most likely to use it would want it
to do.

But I still want a good laser diode electrical model..

 

[Lostgallifreyan]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:zamdnaOrPvgQguzXnZ2dnUVZ_tCdnZ2d@supernews.com:

Lostgallifreyan wrote:
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:xoidnU2- iIbBSu3XnZ2dnUVZ_r6dnZ2d@supernews.com:
As Joerg
said, you're way better off using current drive. It isn't difficult,
just an op amp and a Darlington. Use the Darlington's collector as
the output, and sense the current in its emitter. Adding an outboard
current limit is easy then too.


That's what I intend to try too, though I'll try a MOSFET rather than a
darlington. I take it the darlington is to avoid the gate capacitance
of a MOSFET? I can see that it will work because its total Vf will be
less than the laser diode's own. (A quirk my own circuit is exploiting,
in a different way).

I really like Darlingtons for that job, because they have a lot of
transconductance. That makes the current source stiffer, especially at
low V_CE where MOSFETs start to crap out. Their capacitance is much
lower, which is helpful with massively nonlinear loads like laser
diodes. Also, the V_BE of a Darlington is much better controlled and
less drifty than the V_GS of your average MOSFET. Their betas are
usually around 10,000, which means that they're as accurate as the sense
resistor anyway. Quiet, stable, and predictable--just the ticket for
diode laser drivers, I think.

I've not used them often enough. Always liked the idea though, and I agree
that predictable base current and voltage helps a lot. But unless I'm missing
something, they make great switched but lousy proportional controllers, no?

 

[Joerg]

John Larkin wrote:

On Wed, 29 Jul 2009 12:32:03 -0700, Joerg <invalid@invalid.invalid
wrote:

Lostgallifreyan wrote:

[...]

While I found that a string of four 1N4148's produced a modelled overshoot
almost exactly like what I saw on an oscilloscope months before I considered
looking at spice, I got a very different result when trying four 1N4001's so
it really does need something better than reaching for a standard diode, in a
model OR as a dummy diode in a real circuit (where a optically dead laser
diode is best anyway). So it really comes down to trying to get something
usefully close! EDN's model seems ideal, aimed at solving this problem for
general use, as opposed to the elaborate models in private university
publications. EDN's is probably tested too, proofread and verified before
publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).

"File not found" :-(

Some of the 4000 series behave more like PIN diodes.

The higher-voltage ones ARE pin diodes. They can make excellent drift
step-recovery diodes and impact avalanche diodes. Need 1000 volts in
100 picoseconds?

Do you have some examples and pics? That would be interesting, I have
use the 1N4007 as a RF PIN diode but never as SRD.

One of my next projects needs the opposite, briefly and automatically
disconnecting an RF amp from a several kV pulse path so it doesn't go up
in smoke. The kind of stuff where people often say "you can't do that".
I love it when a project like this comes along.

--
Regards, Joerg

http://www.analogconsultants.com/

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

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7ddv8fF2b3uqiU1@mid.individual.net:

Risque if you want to do 500kHz as you mentioned in another post.


I'm all for pushing the envelope, there's no hide at stake here.
It sure looks like it will work. It's 'competing' with systems that can do
100 or 200 KHz at best generally, and none of these devices are needed to go
further. They work alongside laser systems incapable of more that 10 K, often
as not.

The main point is to see what's possible, and to establish the safe operating
area so when I really want to use this thing I can have a very good idea how
to make it right, at more reasonable figures. And I'll know it will draw a
very clean line, which is what the people most likely to use it would want it
to do.

You can only try that on a breadboard, not SPICE. And then you find out
that it can do 250kHz but after switching to a different manufacturer's
LM317 ... *POOF*

But I still want a good laser diode electrical model..

I'd rather prefer a nice bottle of Chateau d'Yquem

--
Regards, Joerg

http://www.analogconsultants.com/

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

 

[Lostgallifreyan]

Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:AY-dnczxb411gOzXnZ2dnUVZ_r6dnZ2d@supernews.com:

The LM317 has an inductive output characteristic, which resonates with
the bypass cap. The reason for the inductive characteristic is that
there's a feedback loop inside. The output of the 317 is an emitter,
which is naturally low impedance--it's a good voltage source, and the
feedback just makes it a better one. Outside the feedback bandwidth,
it's still a low impedance because it's an emitter.

Collectors make good current sources naturally--a bit of feedback makes
them stiffer and more accurate, but outside the loop bandwidth they're
still current sources. Using an emitter as a current source gives you
problems, because the feedback is fighting the natural tendency of the
device--the output crosses over from a high impedance at low frequency
where feedback dominates, to a low impedance at high frequency where the
feedback is unimportant.

It's a bit like a LDO, where a collector is forced to act like a voltage
source, by wrapping feedback around it, leading to similar sorts of
stability problems.

The usual 317 fixed current source circuit uses a resistor in series
with the output lead, and the feedback lead connected to the other end
of the resistor. That works great for fixed current applications, where
there's nothing to excite the resonance, but if you're using the 317 as
a modulator, you're bound to have trouble with the resonant peak.

Once I'd never have considered it because it has other troubles to overcome
too, I'd used it solely as a fixed constant current drive in every laser I'd
built in the previous 7 years..

One problem is that the series resistor must be on the high side of the load,
most designs using sense resistors put it on the low side. Another is that
1.5V is dropped across that resistor, other designs use far less, so are more
efficient. And another, as you say, is that to damp the feedback for an ideal
response to changes in a supply or load, they fixed conditions that may or
may not be troublesome to us tinkerers who do weird things with it.

The large voltage drop on the sense resistor is actually a boon, it's far
easier to dupe the LM317 accurately when you have that 1.25V to use. I have
modified the idea to drop 1V across the voltage control network leaving just
0.25V on the resistor, saving one watt per amp, pretty cool if you're doing
this with an LM338. > It sucks for fast mod though, stability and solidity
is dire, but it's great for a dimmable low-volt light though, a string of
LED's and that trick, and the efficiency approaches that of a decent switched
power converter.

The high-side sensing seems at first awkward, but it's not that bad, just
feed it to the normal input of a differential amp and do the modulation on
the inverting input. A second stage is needed to set input protections and an
agreeable polarity for response to signals but it's still just one 8 pin
chip.

That internal componentry for response to line.load changes was the thing I
thought would make the concept useless, but that's why reaching 500 KHz with
respectable square waves is so nice a surprise.

Viva the LM317. If I can have 100 of those to do entertaining stuff with it
beats having to agonise over Mouser's lists and paying big tax on many small
boxes. I really aim to do things with a minimal range of parts types, it's a
kind of thing I have..

 

[John Larkin]

On Thu, 30 Jul 2009 10:10:50 -0700, Joerg <invalid@invalid.invalid>
wrote:

John Larkin wrote:
On Wed, 29 Jul 2009 12:32:03 -0700, Joerg <invalid@invalid.invalid
wrote:

Lostgallifreyan wrote:

[...]

While I found that a string of four 1N4148's produced a modelled overshoot
almost exactly like what I saw on an oscilloscope months before I considered
looking at spice, I got a very different result when trying four 1N4001's so
it really does need something better than reaching for a standard diode, in a
model OR as a dummy diode in a real circuit (where a optically dead laser
diode is best anyway). So it really comes down to trying to get something
usefully close! EDN's model seems ideal, aimed at solving this problem for
general use, as opposed to the elaborate models in private university
publications. EDN's is probably tested too, proofread and verified before
publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).

"File not found" :-(

Some of the 4000 series behave more like PIN diodes.

The higher-voltage ones ARE pin diodes. They can make excellent drift
step-recovery diodes and impact avalanche diodes. Need 1000 volts in
100 picoseconds?


Do you have some examples and pics? That would be interesting, I have
use the 1N4007 as a RF PIN diode but never as SRD.

Google "Grehkov diode". He's a Russian guy who discovered the DSRD and
impact avalanche effects in cheap power diodes.

Also look for papers and patents by Thomas E. McEwan.

We did one water-cooled DSRD pulser that makes -2KV pulses, about 2 ns
wide, at 500 KHz. We forward-bias a secret diode at +48 volts for
about 80 ns, to let the current build up to 50 amps or so, then
reverse-bias it from a 400 volt supply and wait for it to snap.

Here's the pulser head...

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

with the serious parts bolted to a gold-plated copper block. A
water-flow cold plate gets bolted to the bottom.

I can show you innards privately. The HV, high power PIN diode turned
out to be unusual.

John

 

[Lostgallifreyan]

"Joel Koltner" <zapwireDASHgroups@yahoo.com> wrote in
news:M3kcm.493202$6p1.228731@en-nntp-02.dc1.easynews.com:

when it's no harder to do it the "right" way?

If you always do everything the 'right' way, how are you going to learn
anything for yourself?

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7de22pF2b171tU1@mid.individual.net:

Remember, laser diodes die quietly. There is no tchk ... *phut* but
there is that painful hit in the bank account.

Ithink I posted enough about that to make it clear I know about that pain.
I'll try it on cheap diodes and take it from there.

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7de27aF2b171tU2@mid.individual.net:

10MHz is sluggishly slow for a decent laser diode.

Not the diode that bothers me. The laser's fast ability is what makes the
idea easier. The question is whether the complexity of other parts of the
system is worth it, and whether in practise a fast graphic scanner shows a
dashed line. That sets limits on ranges for carrier speed. No need to go
faster than is required to avoid that.

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7de2obF2bttf7U2@mid.individual.net:

You can only try that on a breadboard, not SPICE. And then you find out
that it can do 250kHz but after switching to a different manufacturer's
LM317 ... *POOF*

Sure, but again, that's part of the appeal of making widgets that all use a
single device or small number of parts. Means such adjustments don't have to
be made that often. And again, this is as much as exercise in establishing
safe operating areas, as much as anything else...

But I still want a good laser diode electrical model..


I'd rather prefer a nice bottle of Chateau d'Yquem

Does it talk? (Python joke

 

[Joerg]

Lostgallifreyan wrote:

Joerg <invalid@invalid.invalid> wrote in
news:7de2obF2bttf7U2@mid.individual.net:

You can only try that on a breadboard, not SPICE. And then you find out
that it can do 250kHz but after switching to a different manufacturer's
LM317 ... *POOF*


Sure, but again, that's part of the appeal of making widgets that all use a
single device or small number of parts. Means such adjustments don't have to
be made that often. And again, this is as much as exercise in establishing
safe operating areas, as much as anything else...

For a one-off prototype you could be ok.

But I still want a good laser diode electrical model..

I'd rather prefer a nice bottle of Chateau d'Yquem


Does it talk? (Python joke

No, but it can make you talk

--
Regards, Joerg

http://www.analogconsultants.com/

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

 

[Lostgallifreyan]

Joerg <invalid@invalid.invalid> wrote in
news:7de4n6F2cbgsqU1@mid.individual.net:

Lostgallifreyan wrote:
Joerg <invalid@invalid.invalid> wrote in
news:7de2obF2bttf7U2@mid.individual.net:

You can only try that on a breadboard, not SPICE. And then you find
out that it can do 250kHz but after switching to a different
manufacturer's LM317 ... *POOF*


Sure, but again, that's part of the appeal of making widgets that all
use a single device or small number of parts. Means such adjustments
don't have to be made that often. And again, this is as much as
exercise in establishing safe operating areas, as much as anything
else...


For a one-off prototype you could be ok.

Or any number of one-offs. That's actually the idea. Where labour is the
biggest obstacle (lack of automation, and a desire to do as much of it here
as possible), it pays to make a few widgets for a small demand, as one-offs,
and test them individually too. And an LM317 is very convenient, a lot of
function hiding behind three pins, and enough heft to do serious work of its
own. It's a very attractive device and saves a LOT of board layout work.

But I still want a good laser diode electrical model..

I'd rather prefer a nice bottle of Chateau d'Yquem


Does it talk? (Python joke


No, but it can make you talk

Careful what you wish for! > I have a hair trigger as this thread shows..

 

[Joerg]

John Larkin wrote:

On Thu, 30 Jul 2009 10:10:50 -0700, Joerg <invalid@invalid.invalid
wrote:

John Larkin wrote:
On Wed, 29 Jul 2009 12:32:03 -0700, Joerg <invalid@invalid.invalid
wrote:

Lostgallifreyan wrote:
[...]

While I found that a string of four 1N4148's produced a modelled overshoot
almost exactly like what I saw on an oscilloscope months before I considered
looking at spice, I got a very different result when trying four 1N4001's so
it really does need something better than reaching for a standard diode, in a
model OR as a dummy diode in a real circuit (where a optically dead laser
diode is best anyway). So it really comes down to trying to get something
usefully close! EDN's model seems ideal, aimed at solving this problem for
general use, as opposed to the elaborate models in private university
publications. EDN's is probably tested too, proofread and verified before
publishing.

http://www.e-insite.net/ednmag/archives/1998/071698/pdf/15di.pdf
(Halfway through file).

"File not found" :-(

Some of the 4000 series behave more like PIN diodes.
The higher-voltage ones ARE pin diodes. They can make excellent drift
step-recovery diodes and impact avalanche diodes. Need 1000 volts in
100 picoseconds?

Do you have some examples and pics? That would be interesting, I have
use the 1N4007 as a RF PIN diode but never as SRD.

Google "Grehkov diode". He's a Russian guy who discovered the DSRD and
impact avalanche effects in cheap power diodes.

Also look for papers and patents by Thomas E. McEwan.

Thanks, I will check that out.

We did one water-cooled DSRD pulser that makes -2KV pulses, about 2 ns
wide, at 500 KHz. We forward-bias a secret diode at +48 volts for
about 80 ns, to let the current build up to 50 amps or so, then
reverse-bias it from a 400 volt supply and wait for it to snap.

Here's the pulser head...

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

with the serious parts bolted to a gold-plated copper block. A
water-flow cold plate gets bolted to the bottom.

I can show you innards privately. The HV, high power PIN diode turned
out to be unusual.

That would be nice. My "Reply to" address is valid as is and lands in my
biz inbox. But only if you feel comfortable doing that.

Was this the project from several years ago that started with the FR804?
Take a look at this puppy, fresh out of the gate:

http://www.nxp.com/acrobat_download/datasheets/BYV29FX-600_1.pdf

In the project coming up I need a lot more volts though (10kV range) and
it has to be small.

--
Regards, Joerg

http://www.analogconsultants.com/

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