Re: Spice models of laser diodes?
Lostgallifreyan
news:Xns9C50420FC1...@216.196.109.145:
> Does anyone have any spice models of DVD writer type laser diodes?
> Possibly anything will do, I just want to explore whether there's much
> point to modelling with them, or whether it's enough to set soem basic
> parameters. I'm totally new to spice so I have no idea. But I know that
> many laser diodes are very sparsely documented, so the idea alone that
> someone might have spice- modelled one is entertaining, if nothing else.
>
In case anyone's following this (and I opened it from alt.lasers to two
electronics newsgroups), I'm still after laser diode spice models...
And I found this:
http://www.freeda.org/doc/elements/dhld.html
I'm still very new to spice, so if anyone is feeling very helpful and can
write a conversion of this I can use in LTspice, please do.
Also, a quote of my earlier posts so people in the electronics groups can see
them:
"I've seen a few lines specifying diode models last night and gathered some
for general use, and I'll look into what the parameters mean, so even a few
known ones in spice format will help me, even without a full model. But I do
want to know what parameters are important to laser diodes, and what values
they ought to have for a DVD writer diode. I suspect they will be similar for
most if not all DVD diodes.."
And:
"Does anyone have access to the Journal of Lightwave Technology vol.15, no.4,
april 1997, page 717? I read that there's a spice model there, but I have no
access to this."
In short, I want electrical models of DVD writer type diodes. I don't need
extreme accuracy, or the optical details, (didn't think spice went there
anyway). They just have to be realistic electrically, and I'd like some
simple direct guidance on what parameters I need to change in an LTspice
model of a diode, as that's the context I'm using.
Lostgallifreyan
Lostgallifreyan
http://www.avtechpulse.com/faq.html/IV.33/
I'm studying that as best I can but it's fairly heavyweight, can anyone help
me understand how to use it?
They mention terms like TT (apparently in microseconds, for 'transit time')
but they don't say where they get it from. I don't see it in the two diode
data sheets I tried to find it in, only reverse recovery time, and if it were
the same thing, surely the notation would be same, and it's not. The deeper I
look, the thicker looks the plot.
I'll be patient now and lay off the posting because this looks more complex
than I thought, and might take time to answer. Please do though, if you know
how. I don't mind doing the work but I need to be shown what must be done,
and where to get the data I need to start with. Right now I don't even know
if it IS possible to translate from data sheet to spice model, and it looks
like it isn't.
Time for the serious boffins to duke it out in this thread, if they're
interested. :)
o...@uakron.edu
> Time for the serious boffins to duke it out in this thread, if they're
> interested. :)
ask over on sci.optics.fiber
Steve
Lostgallifreyan
0549e4...@k1g2000yqf.googlegroups.com:
> ask over on sci.optics.fiber
>
For an electrical model? Fibre is specifically optical... The people who I
think can answer this hang out in the groups I posted to anyway.
John Larkin
<no-...@nowhere.net> wrote:
>Progress...?
>http://www.avtechpulse.com/faq.html/IV.33/
>
>I'm studying that as best I can but it's fairly heavyweight, can anyone help
>me understand how to use it?
>
>They mention terms like TT (apparently in microseconds, for 'transit time')
>but they don't say where they get it from. I don't see it in the two diode
>data sheets I tried to find it in, only reverse recovery time, and if it were
>the same thing, surely the notation would be same, and it's not. The deeper I
>look, the thicker looks the plot.
>
We bought some 850 nm fiber-type laser diodes that acted as if they
had a microseconds-response PIN diode built into them, in series with
the actual laser. If you applied current suddenly, the voltage would
overshoot almost 2:1, as if there were an inductor in series. As long
as the current wasn't cut off for too many nanoseconds, it behaved
like a diode. Fine for telecom and maybe for burning CDs, but terrible
for sending baseband on/off digital stuff.
John
Hal Murray
John Larkin <jjla...@highNOTlandTHIStechnologyPART.com> writes:
>We bought some 850 nm fiber-type laser diodes that acted as if they
>had a microseconds-response PIN diode built into them, in series with
>the actual laser. If you applied current suddenly, the voltage would
>overshoot almost 2:1, as if there were an inductor in series. As long
>as the current wasn't cut off for too many nanoseconds, it behaved
>like a diode. Fine for telecom and maybe for burning CDs, but terrible
>for sending baseband on/off digital stuff.
The telcom guys are using baseband. They use scramblers to ensure
that there are enough transitions to do clock recovery. There isn't
much low freqency energy.
What sort of data were you sending? Were there long strings of
1s or 0s?
I seem to remember something about not turning something all the
way off. I have forgotten the context and reasoning.
I think the idea was to modulate it from 10% to 100% rather
than turn it all the way off in order to avoid transients/problems
like you described.
It might have been incandescent lamps, but I don't think so. Reminds me
of the time I went into a dark machine room many many years ago.
(I was sleeping on the couch, babysitting for an all night run.)
All the red lights on the disks were on. Wow were we in trouble!
After a few seconds I figured out that it was just the keep-warm
current to avoid the turn-on transient. Nothing was visible in
normal room light.
--
These are my opinions, not necessarily my employer's. I hate spam.
Lostgallifreyan
sure it's electro-optical in nature..
Lostgallifreyan
news:Xns9C512D9705D...@216.196.109.145:
> Definitely a communications breakdown spreading here but I'm not entirely
> sure it's electro-optical in nature..
>
Does anyone here know how to adapt a diode model for a laser diode?
Lostgallifreyan
I now have (thanks Marco) two models that look like detailed internal models
(the other being one I mentioned finding earlier), but still no answer at all
on the basic diode modelling. It's likely I'll mostly need a minimal
behavioural model so adapting an existing diode model to mimic a moderately
powerful GaAlAs based single mode laser diode might be enough at times. How?
Please tell me. I'll continue to hunt but I want help if I can get it. Data
sheets specs seem to bear no clear relation to spice model data. There
doesn't seem to be any way in a standard diode spice model to set the Vf, for
example. What do I do?
Here's a datasheet for one I'll most likely start with:
http://www.datasheetarchive.com/RLD65PZB5-datasheet.html
Please tell me how I convert the important specs in that to a basic diode
model that behaves well enough to design simple modulated drivers for.
Lostgallifreyan
all of it.
Ok, I tried this, and I don't think it's going to work.
I corrected some typos (very few, Marco did a good job given that the
original makes it very hard to see what is or is not a space), one of which
is definitely in the original text, a + beginning a line without which SPICE
can't run because it needs that to indicate continuation. It's safe to say
there might be more errors given the results of running it. First, my typo-
edited copy, which runs in LTspice:
ibias 0 p 10m
xlaser p 0 pf ltest1
rout pf 0 1e9
************************************************************************
.subckt ltest1 p n pf
D1 p nt1 d1mod_ltest1
Ic1 p nt1 3.6641713e-14
Vt1 nt1 n 0
D2 p n d2mod_ltest1
Ic2 p n 3.6641713e-14
Br1 p n i=0*i(Vt1) +20701.692*i(Vt1) *i(Vt1)+28862208
*i(Vt1)*i(Vt1)*i(Vt1)
Bs1 p n i=1.3785977*v(m) *v(m)*ln(1e-60 +5220.1829*i(Vt1)+
+ 54033309*i(Vt1) *i(Vt1)+7.5333001e +10*i(Vt1)*i(Vt1)*i(Vt1))/
+ (1+0.95928574
+ *v(m)*v(m))
Rph m 0 1
Cph m 0 5.518e-12
Br2 0 m i=(0*i(Vt1) +1.0120369*i(Vt1) *i(Vt1)+0*i(Vt1)
*i(Vt1)*I(Vt1))/v(m)
Bs2 0 m i=0.67395059 *v(m)*ln(1e-60 +5220.1829*i(Vt1)
+54033309*i(Vt1)*i(Vt1)+
+ 7.5333001e +10*i(Vt1)*i(Vt1) *i(Vt1))/(1+0.95928574 *v(m)*v(m))
Bpf pf 0 v=v(m)*v(m)
.ends ltest1
.model d1mod_ltest1 D Is=3.6641713e-14 n=2
.model d2mod_ltest1 D Is=3.6641713e-14 n=2 tt=1.8181818e-08
************************************************************************
.dc ibias 0 50m 0.25m
.end
Third of three vertically aligned + signs was absent from original, and is
vital unless you merge that line to the end of the previous one.) I made a
symbol file for LTspice to use this model:
Version 4
SymbolType CELL
LINE Normal -12 -40 -12 -24
LINE Normal -20 -32 -4 -32
LINE Normal -20 32 -4 32
LINE Normal -28 32 -48 32
LINE Normal -28 -32 -48 -32
LINE Normal 76 0 96 0
LINE Normal 48 -16 -16 -16
LINE Normal 16 16 48 -16
LINE Normal -16 -16 16 16
LINE Normal 48 16 -16 16
SYMATTR Value ltest1
SYMATTR Prefix X
SYMATTR ModelFile LD_TEST.sub
SYMATTR Value2 ltest1
SYMATTR Description Unknown laser diode model.
PIN -48 -32 NONE 0
PINATTR PinName PIN+
PINATTR SpiceOrder 1
PIN -48 32 NONE 0
PINATTR PinName PIN-
PINATTR SpiceOrder 2
PIN 96 0 NONE 0
PINATTR PinName OUT
PINATTR SpiceOrder 3
Ignore the terrible graphic if you try this, it was a rough edit of one of my
op-amp symbols, it was the fastest way to make something useable...
Anyway, it's an odd result! If I make a simple LM317 based constant current
driver circuit (I have a good LM317 model now) and set the current for 152 mA
using an 8R2 resistor, the current is steady but at more current than it
should be! The model appears to be generating virtual energy. :) Worse, a
voltage plot of the anode end shows a rediculous curve, a relaxation
oscillator type sawtooth varying once every 50 microseconds, and between 0V
(Ground) and MINUS 12 KILOVOLTS! That can NOT be right...
I really don't think I'm going to use this. And I suspect we wouldn't have to
be bombed back to the stone age, or even to the technical levels current when
the Alexandria Library was burned, to render that document as arcane as one
of Harry Potter's spells. It's obviously not meant for the purpose I'm trying
to put it to even if by a wild fluke I can figure out how to make it work
right, and I don't think I even have leave to SEE it, technically, so I ask
yet again, please can someone help me to find how to adapt a standard diode
model to emulate a laser diode, electrically, well enough to design simple
drivers for? I need to see if learning SPICE is going to be useful. So far I
notive very different behaviour depending on whether I use 4 series 1N4005's
or 4 series 1N4148's, so clearly I do need something better than plugging in
the first diodes I can find.
Kai-Martin Knaak
> So far I
> notive very different behaviour depending on whether I use 4 series
> 1N4005's or 4 series 1N4148's, so clearly I do need something better
> than plugging in the first diodes I can find.
Whatever circuit you are going to use, it shouldn't be that sensitive to
the properties of the diode. Unless you intend to do some very high
bandwidth modulation, any diode should do in the simulation.
There's no need to reinvent the wheel here. Did you check the collection
of laser diode drivers in sam's laserfaq?
---<(kaimartin)>---
--
Kai-Martin Knaak
Öffentlicher PGP-Schlüssel:
http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x6C0B9F53
Lostgallifreyan
news:pan.2009.07...@lilalaser.de:
> On Mon, 27 Jul 2009 19:09:42 -0500, Lostgallifreyan wrote:
>
>> So far I
>> notive very different behaviour depending on whether I use 4 series
>> 1N4005's or 4 series 1N4148's, so clearly I do need something better
>> than plugging in the first diodes I can find.
>
> Whatever circuit you are going to use, it shouldn't be that sensitive to
> the properties of the diode. Unless you intend to do some very high
> bandwidth modulation, any diode should do in the simulation.
>
> There's no need to reinvent the wheel here. Did you check the collection
> of laser diode drivers in sam's laserfaq?
>
> ---<(kaimartin)>---
Several times. :) I'm after trying something very specific, something I was
often told wouldn't work well but has often exceeded expectations so I want
to see how far it goes.. I'm modulating up to 500 MHz, DC coupled, with
constant regulated current held in linear proportion to an input control
voltage between 0 and 5 volts, with independent control of threshold level.
I have no illusions about spice. I've always preferred to model ideas as
parts on boards, but having seen LTspice mentioned a lot, I started looking
at it, and decided to learn something new because like SketchUp for basic
aid in visualising hardware constructions, this should save a lot of time
eventually.
I found that my FIRST attempt to model my driver showed me details I saw on a
100 MHz scope many months ago, so it's obviously damn close to the mark. I
was modulating at just 100 KHz then, trying to see if I could out-do Robin
Bowden's Die4drive. :) (Does 200 KHz with no overshoot but with wave peaks
far less flat than I want over their duration at that speed). The spice model
showed that some resistor changes were enough to increase stability to allow
500 KHz modulation with sharp transitions, flat peaks, AND no overshoot, (and
well over 1 MHz if I don't mind blunting the sharp edges and rounding the
peaks a bit), and at those frequencies you can bet it DOES matter what diode
properties there are if you're trying to keep sharp edges... in general I
notice from models that those diodes which do not vary their Vf much with
sharp changes from 0 drive to full drive are also those most prone to ringing
and overshoot on the rising edge.
Right now I'm about 24 hours overdue for sleep and past feeling tired but I'm
going to try to get some. I've started trying some LED models that are as
close as anything yet. They have forward voltage similar to a laser diode,
similar average currents, and they produce roughly the expected kinds of
waveforms. Maybe this is enough closeness, so if during my sleep people
shower my posts liberally with spice models of high-brightness red GaAlAs
LED's as well as laser diodes, I'll be very happy to see them in how ever
many hours it takes me to be fit to look at them.
And as a hint, my diode driver is a modification of one I posted here often,
in turn based on an idea in the LaserFAQ, posted originally by Winfield Hill.
His wouldn't have accepted a control voltage though, that bit was mine.
Lostgallifreyan
found what might be a way.
Intusoft make a tool called SpiceMod which is part of a package they call
ICAP4 though it seems the demo setup doesn't have that tool, just some very
good noted on it, and modelling in general:
The file WkwModels.pdf from the demo install answers a lot fo the questions I
had about modelling diodes, which parameters to tweak, and extraction from
data sheets.
I don't know if the lack of response to me is because of a thousand experts
silently screming RTFM at me, or because it's actually asomething they DON'T
KNOW. Given that Intusoft explain that this is a serious challenge for
experts too, I'm assuming maybe they really don't know, so they might benefit
from that file as much as I will.
Joerg
Most of us just use a regular diode to simulate because all one
(usually) wants to know is that there definitely won't be any ever so
slight spike in diode current because LDs can go poof in microseconds.
Simulating the optics part would be a major challenge, I think.
--
Regards, Joerg
http://www.analogconsultants.com/
"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Lostgallifreyan
news:7dbdd3F...@mid.individual.net:
> Lostgallifreyan wrote:
>> If anyone is following this and wants to try modelling their own stuff,
>> I found what might be a way.
>> Intusoft make a tool called SpiceMod which is part of a package they
>> call ICAP4 though it seems the demo setup doesn't have that tool, just
>> some very good noted on it, and modelling in general:
>> The file WkwModels.pdf from the demo install answers a lot fo the
>> questions I had about modelling diodes, which parameters to tweak, and
>> extraction from data sheets.
>>
>> I don't know if the lack of response to me is because of a thousand
>> experts silently screming RTFM at me, or because it's actually
>> asomething they DON'T KNOW. Given that Intusoft explain that this is a
>> serious challenge for experts too, I'm assuming maybe they really don't
>> know, so they might benefit from that file as much as I will.
>
>
> Most of us just use a regular diode to simulate because all one
> (usually) wants to know is that there definitely won't be any ever so
> slight spike in diode current because LDs can go poof in microseconds.
> Simulating the optics part would be a major challenge, I think.
>
Thought that might provoke an expert. :) I agree, same here, that's all I
usually need too, though like that EDN manual says, a more detailed model
that allows models to give warning of imminent demise is useful. Modelling
for ESD is likely daft, better that we just take care and put in TVS's and
such, but when it comes to fast modulation, a model definitely helps. Surely
you'd have a use for that, no?
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).
If anyone can help by making that into asy and sub files for LTspice it will
help me a lot, and probably a lot of other people too. Four days of searching
have found lots of other people askign questions, and very few answers, and
NONE complete and verified. Someone could get well known for solving this so
other people can have an easier time of it.
Lostgallifreyan
checked it carefully, so this can save you a bit of time:
Vlas 100 50 1
Dlas 50 200 diode1
F1 0 1 Vlas 1
Rs 1 0 {Sm*sps}
I1 2 0 {Sm*sps*Ith*exp((T/25)-1)}
G1 0 2 1 0 1
Rlim 2 0 1Meg
Ds 2 3 diode
Vm 3 0 0
F2 300 400 Vm 1
Dmon 300 400 diode
Cmon 300 400 Cmon
.model diode d
.model diode d rs=5
.ENDS
But it obviously needs more than that to build a subcircuit file. I don't
know how yet, or even if the 'figure 1' in that PDF has all the required
detail to make it possible.
Joerg
I have designed LD circuitry but I am not an expert. Senor Hobbs would
be one. TVS don't work well. Their cutoff isn't terribly well defined
and they have too much capacitance for this. Just handle the things with
care. I've never killed one with ESD, knock on wood ;-)
> 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.
> If anyone can help by making that into asy and sub files for LTspice it will
> help me a lot, and probably a lot of other people too. Four days of searching
> have found lots of other people askign questions, and very few answers, and
> NONE complete and verified. Someone could get well known for solving this so
> other people can have an easier time of it.
It's going to be lots of work. You'll need to get into behavioral models
and while people have modeled large chunks of jet engines with that it
was a ton of work.
Lostgallifreyan
news:7dbmdvF...@mid.individual.net:
Sorry, right file, wrong location. Try this:
http://www.edn.com/archives/1998/071698/pdf/15di.pdf
> Some of the 4000 series behave more like PIN diodes.
>
>
>> If anyone can help by making that into asy and sub files for LTspice it
>> will help me a lot, and probably a lot of other people too. Four days
>> of searching have found lots of other people askign questions, and very
>> few answers, and NONE complete and verified. Someone could get well
>> known for solving this so other people can have an easier time of it.
>
>
> It's going to be lots of work. You'll need to get into behavioral models
> and while people have modeled large chunks of jet engines with that it
> was a ton of work.
>
I've been finding (and been sent) spice models that are in various stages of
completion and complexity. Ignoring the rest for now, I'm focussing on that
EDN one because it looks like it's meant to be complete. But it's NOT in a
single subcircuit file that can be adapted to LTspice, or anything else. I
don't think it needs modelling, just translation.
For modelling, I'll look into that too, as equations are given in that PDF
file I mentioned earlier, from Intusoft. In their descriptions of how to use
SpiceMod (which I learned costs 600 bucks(!) and is therefore the most
expensive few tens of kilobytes I've ever heard of) they show a screen that
neatly prioritises the data sheet specs for pluging into the equations. While
the details for transisotrs (bar a MOSFET) are not similarly revealed, there
ought to be enough there in their diode explanations to model a laser diode,
electrically. But again, all I'm asking for here right now is for someone who
knows how, to translate that EDN article to a subcircuit ready to plug into
LTspice. (I can make my own symbol file).
Lostgallifreyan
news:7dbmdvF...@mid.individual.net:
> I have designed LD circuitry but I am not an expert. Senor Hobbs would
> be one. TVS don't work well. Their cutoff isn't terribly well defined
> and they have too much capacitance for this. Just handle the things with
> care. I've never killed one with ESD, knock on wood ;-)
>
Interesting. Robin Bowden didn't make strong recommendations for them either.
Just a resistor/capacitor network, and a zener. I concur, though at the time
I was all for varistors too as I'd found a LOT fo them cheaply on eBay at the
time.. But they apparently change characteristics rapidly over time fi they
see anything like the conditions they have to limit, so I'm not too keen now.
> Some of the 4000 series behave more like PIN diodes.
>
Trying not to get away from the focus of the thread because I really do want
direct help with model translation as it's unlikely I can do it alone, but
this IS interesting to me.. PIN are those fast photodiodes, right? Often used
for detecting very short laser pulses and such? When I modelled my driver
using the 1N4005 model I found, I got a lot of ringing. I also saw a
correlation with the changing of Vf with hard changes between zero and full
drive. I analogised it with the hitting of a hard object as opposed to a
softer one that inherently damps the impact. If a PIN diode is to respond
fast it seems reasonable to think that it is capable of hard brittle
responses, otherwise it could not hope to react in time to register a very
short laser pulse. Is this a reasonable way to view it? And if so, why so
with rectifiers and not signal diodes? Or LED's which I imagine are similar
to laser diodes, being usually GaAs based.
Lostgallifreyan
news:Xns9C57D85EDFF...@216.196.109.145:
> I also saw a
> correlation with the changing of Vf with hard changes between zero and
> full drive.
Meaning: Diode models with little change in Vf with current at 500 KHz square
wave drive were also those which rang the most.
Joerg
> Joerg <inv...@invalid.invalid> wrote in
>
>> 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" :-(
>>
>
> Sorry, right file, wrong location. Try this:
> http://www.edn.com/archives/1998/071698/pdf/15di.pdf
>
Well, laser diodes are a lot more complicated that this simple model.
Onset of lasing which happens sort of digital at xx percent of max
current, non-linear relationship between output and input power,
overload behavior, wavelength drift with heat and so on.
>> Some of the 4000 series behave more like PIN diodes.
>>
>>
>>> If anyone can help by making that into asy and sub files for LTspice it
>>> will help me a lot, and probably a lot of other people too. Four days
>>> of searching have found lots of other people askign questions, and very
>>> few answers, and NONE complete and verified. Someone could get well
>>> known for solving this so other people can have an easier time of it.
>>
>> It's going to be lots of work. You'll need to get into behavioral models
>> and while people have modeled large chunks of jet engines with that it
>> was a ton of work.
>>
>
> I've been finding (and been sent) spice models that are in various stages of
> completion and complexity. Ignoring the rest for now, I'm focussing on that
> EDN one because it looks like it's meant to be complete. But it's NOT in a
> single subcircuit file that can be adapted to LTspice, or anything else. I
> don't think it needs modelling, just translation.
>
> For modelling, I'll look into that too, as equations are given in that PDF
> file I mentioned earlier, from Intusoft. In their descriptions of how to use
> SpiceMod (which I learned costs 600 bucks(!) and is therefore the most
> expensive few tens of kilobytes I've ever heard of) they show a screen that
> neatly prioritises the data sheet specs for pluging into the equations. While
> the details for transisotrs (bar a MOSFET) are not similarly revealed, there
> ought to be enough there in their diode explanations to model a laser diode,
> electrically. But again, all I'm asking for here right now is for someone who
> knows how, to translate that EDN article to a subcircuit ready to plug into
> LTspice. (I can make my own symbol file).
Seriously, it's a lot more intricate than that. Just to give you an
example from the non-LD world: One of the transistor models of an
amplifier I recently ran is about two dozen lines of SPICE entries.
Those are the sims where the fans come on hard and the office temp
creeps up another 3F or so.
I don't think you'll get around behavioral models here.
Joerg
> Joerg <inv...@invalid.invalid> wrote in
> news:7dbmdvF...@mid.individual.net:
>
>> I have designed LD circuitry but I am not an expert. Senor Hobbs would
>> be one. TVS don't work well. Their cutoff isn't terribly well defined
>> and they have too much capacitance for this. Just handle the things with
>> care. I've never killed one with ESD, knock on wood ;-)
>>
>
> Interesting. Robin Bowden didn't make strong recommendations for them either.
> Just a resistor/capacitor network, and a zener. I concur, though at the time
> I was all for varistors too as I'd found a LOT fo them cheaply on eBay at the
> time.. But they apparently change characteristics rapidly over time fi they
> see anything like the conditions they have to limit, so I'm not too keen now.
>
How do you want to protect a laser diode with any of these?
>> Some of the 4000 series behave more like PIN diodes.
>>
>
> Trying not to get away from the focus of the thread because I really do want
> direct help with model translation as it's unlikely I can do it alone, but
> this IS interesting to me.. PIN are those fast photodiodes, right? Often used
> for detecting very short laser pulses and such? When I modelled my driver
> using the 1N4005 model I found, I got a lot of ringing. I also saw a
> correlation with the changing of Vf with hard changes between zero and full
> drive. I analogised it with the hitting of a hard object as opposed to a
> softer one that inherently damps the impact. If a PIN diode is to respond
> fast it seems reasonable to think that it is capable of hard brittle
> responses, otherwise it could not hope to react in time to register a very
> short laser pulse. Is this a reasonable way to view it? And if so, why so
> with rectifiers and not signal diodes? Or LED's which I imagine are similar
> to laser diodes, being usually GaAs based.
Photodiodes are reverse biased if you need speed while PIN diodes used
as controlled RF resistors are forward biased and the current sets the
resistance. But that works only if the carrier lifetime is sufficient
for the frequencies it has to work at.
For more data regarding LD models I'd get in contact with a few
university research labs. It is not a trivial task at all.
Phil Hobbs
> Lostgallifreyan wrote:
<snip>
>> Thought that might provoke an expert. :) I agree, same here, that's
>> all I usually need too, though like that EDN manual says, a more
>> detailed model that allows models to give warning of imminent demise
>> is useful. Modelling for ESD is likely daft, better that we just take
>> care and put in TVS's and such, but when it comes to fast modulation,
>> a model definitely helps. Surely you'd have a use for that, no?
>>
>
> I have designed LD circuitry but I am not an expert. Senor Hobbs would
> be one. TVS don't work well. Their cutoff isn't terribly well defined
> and they have too much capacitance for this. Just handle the things with
> care. I've never killed one with ESD, knock on wood ;-)
>
>
>> 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" :-(
Try:
http://preview.tinyurl.com/mfg8g8
> Some of the 4000 series behave more like PIN diodes.
>
>
Yeah, they can take _forever_ to turn on. Not much use for protection
diodes in most cases.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Joerg
Thanks, by now I've seen it. But the model presented ain't much to write
home about, IMHO.
>> Some of the 4000 series behave more like PIN diodes.
>>
>>
> Yeah, they can take _forever_ to turn on. Not much use for protection
> diodes in most cases.
>
OTOH, for the RF guy their are very close to the definition of a free
lunch :-)
Lostgallifreyan
news:7dbqhaF...@mid.individual.net:
> For more data regarding LD models I'd get in contact with a few
> university research labs. It is not a trivial task at all.
>
EDN (who I trust quite deeply on matters of useful working ideas) seem to
think that a moderately simple diode model can be enough when making basic
driver models. All I'm asking for is translation of that model to a
subcircuit file I can use in LTspice. I'm new to spice but it's already clear
to me that it is UNWISE to model more detail than is strictly needed. So I
think EDN have the right idea. I'm after something that other people can
also easily use and benefit from, I'm not after a perfect detailed model I
can win prizes with.
Lostgallifreyan
news:xq6dneoJYJOZK-3X...@supernews.com:
> Yeah, they can take _forever_ to turn on. Not much use for protection
> diodes in most cases.
>
I'm not after protection diodes. I knew I should NOT have digressed into that
point. All I'm asking for is a translation to LTspice, for that EDN idea. I
typed out the net list to help, but that's all I know how to do right now.
Lostgallifreyan
news:7dbrk7F...@mid.individual.net:
> Thanks, by now I've seen it. But the model presented ain't much to write
> home about, IMHO.
>
>
I read somewhere that it was a better version of an earlier one in a Pspice
library. How good does it have to be? No point in modelling more detail than
needed as a starting point. We don't even HAVE that much, any of us hobbyists
and small scale designers. If experts raise their hands in horror saying
there's no point in simple modelling rather than too much detail (with which
Intusoft, who really know this stuff, would solidly disagree), then we'll all
continue to have nothing to go on except dead laser diodes! Surely someone
who knows how might change this?
Phil Hobbs
Wow, for you a free lunch must be _really_ free!
Joerg
You'll have to do that piece by piece. LTSpice's preferred method is
graphics entry. For example, instead of writing out the netlist line for
G you place a voltage dependent current source via point and click and
connect it up in the schematic editor.
If you are new to SPICE I strongly suggest not to start with a project
like this but first use some of the supplied "jigs" or example circuits
and play around with those. Unless you really understand the program it
is very easy to reach wrong sim results.
Phil Hobbs
I know, it's just an interesting point.
<Obligatory on-topic content>
I rather suspect you're barking up the wrong tree with a SPICE model of
a diode laser...it isn't the terminal voltage you care about, it's the
light output, and that depends on a whole lot of optical and thermal
things that SPICE is never, ever going to get right. They have widely
differing timescales, for one thing, which SPICE is horrible at, and for
another thing, small amounts of optical feedback have a _huge_ effect on
DL performance, including feeding back to the terminal voltage.
</Obligatory on-topic content>
Joerg
> Joerg <inv...@invalid.invalid> wrote in
> news:7dbrk7F...@mid.individual.net:
>
>> Thanks, by now I've seen it. But the model presented ain't much to write
>> home about, IMHO.
>>
>>
>
> I read somewhere that it was a better version of an earlier one in a Pspice
That depends on you. If you want the sims to model all the way to
failure modes I'd really be surprised if PSPICE had something in a
library that would even come close. My PSPICE license is too old so I
wouldn't know. But that would be one tough job.
Again, a laser diode is not a linear device when you look at lasing
output. Not at all.
> ... No point in modelling more detail than
> needed as a starting point. We don't even HAVE that much, any of us hobbyists
> and small scale designers. If experts raise their hands in horror saying
> there's no point in simple modelling rather than too much detail (with which
> Intusoft, who really know this stuff, would solidly disagree), ...
Let them disagree. Will they pay for your dead laser diodes?
> ... then we'll all
> continue to have nothing to go on except dead laser diodes! Surely someone
> who knows how might change this?
All I am saying is that I believe it is impossible to correctly model a
laser diode by trying to find electrical equivalents for all its
behaviors. You need a behavioral model in addition. All it takes for a
LD to die is optical overload inside the cavity. A brief wiggle of a
fiber connector, a spike of a few usec ... poof. The EDN model isn't
helping you with that.
Lostgallifreyan
news:7dbt02F...@mid.individual.net:
> You'll have to do that piece by piece. LTSpice's preferred method is
> graphics entry. For example, instead of writing out the netlist line for
> G you place a voltage dependent current source via point and click and
> connect it up in the schematic editor.
>
I suspected as much. :) Actually my guess is that their equivalent circuit
needs to be constructed then turned into a subcircuit. There's no doubt it
CAN ultimately be written as a single subcircuit file, I don't know why EDN's
contributor didn't go all the way.
> If you are new to SPICE I strongly suggest not to start with a project
> like this but first use some of the supplied "jigs" or example circuits
> and play around with those. Unless you really understand the program it
> is very easy to reach wrong sim results.
>
I always reality-check things. I only intend to use LTspice the way I do my
case designs and other physical models in SketchUp. Sure, a posh CAD tool can
design me a proper screw thread while SketchUp hasn't a chance of this (at
least, not the version 4 I choose to stay with), but the idea is to quickly
aid visualisation, not to substitute for reality.
Lostgallifreyan
news:7dbtfqF...@mid.individual.net:
> Lostgallifreyan wrote:
>> Joerg <inv...@invalid.invalid> wrote in
>> news:7dbrk7F...@mid.individual.net:
>>
>>> Thanks, by now I've seen it. But the model presented ain't much to
>>> write home about, IMHO.
>>>
>>>
>>
>> I read somewhere that it was a better version of an earlier one in a
>> Pspice library. How good does it have to be? ...
>
>
> That depends on you. If you want the sims to model all the way to
> failure modes I'd really be surprised if PSPICE had something in a
> library that would even come close. My PSPICE license is too old so I
> wouldn't know. But that would be one tough job.
>
> Again, a laser diode is not a linear device when you look at lasing
> output. Not at all.
No, but I'm looking at electrical INput..
>
>
>> ... No point in modelling more detail than
>> needed as a starting point. We don't even HAVE that much, any of us
>> hobbyists and small scale designers. If experts raise their hands in
>> horror saying there's no point in simple modelling rather than too much
>> detail (with which Intusoft, who really know this stuff, would solidly
>> disagree), ...
>
>
> Let them disagree. Will they pay for your dead laser diodes?
>
No, but they DO take my point when I tell them that SpiceMod shouldn't cost a
personal user more than a very few of them. :)
>
>> ... then we'll all
>> continue to have nothing to go on except dead laser diodes! Surely
>> someone who knows how might change this?
>
>
> All I am saying is that I believe it is impossible to correctly model a
> laser diode by trying to find electrical equivalents for all its
> behaviors. You need a behavioral model in addition. All it takes for a
> LD to die is optical overload inside the cavity. A brief wiggle of a
> fiber connector, a spike of a few usec ... poof. The EDN model isn't
> helping you with that.
>
Well, Tim G at Intusoft kindly said if I sent him some model numbers, he'd
see what he can do. I sent him 5 data sheets. :) Got to try my luck, no?
Besides, they might give a workable average for the kinds of high power red
single mode diodes hobbyists are using.
From what I've seen of my dead diodes, they are still electrically very
similar to live ones so I'm not concerned with advanced optical modelling.
Lostgallifreyan
5ZRI-3XnZ2d...@supernews.com:
> I rather suspect you're barking up the wrong tree with a SPICE model of
> a diode laser...it isn't the terminal voltage you care about, it's the
> light output, and that depends on a whole lot of optical and thermal
> things that SPICE is never, ever going to get right. They have widely
> differing timescales, for one thing, which SPICE is horrible at, and for
> another thing, small amounts of optical feedback have a _huge_ effect on
> DL performance, including feeding back to the terminal voltage.
>
During the transitions, perhaps, but in steady state operation there seems to
be a remarkable electrical similarity between a dead diode and a live one.
What matters is the way the diode responds to hard electrical changes on the
input, as that's what makes the ringing and damaging overshoots. This is true
with NO consideration of optical nature, and just modelling that alone,
realistically for real laser diodes, is a lot more than we currently have.
And likely not that big an ask, it's just not been done much, it seems.
Joerg
> Joerg <inv...@invalid.invalid> wrote in
> news:7dbt02F...@mid.individual.net:
>
>> You'll have to do that piece by piece. LTSpice's preferred method is
>> graphics entry. For example, instead of writing out the netlist line for
>> G you place a voltage dependent current source via point and click and
>> connect it up in the schematic editor.
>>
>
> I suspected as much. :) Actually my guess is that their equivalent circuit
> needs to be constructed then turned into a subcircuit. There's no doubt it
> CAN ultimately be written as a single subcircuit file, I don't know why EDN's
> contributor didn't go all the way.
>
Yes, it should be feasible to place it in a subcircuit. However, since
you said you just started out with LTSpice I suggest not to do that (yet).
>> If you are new to SPICE I strongly suggest not to start with a project
>> like this but first use some of the supplied "jigs" or example circuits
>> and play around with those. Unless you really understand the program it
>> is very easy to reach wrong sim results.
>>
>
> I always reality-check things. I only intend to use LTspice the way I do my
> case designs and other physical models in SketchUp. Sure, a posh CAD tool can
> design me a proper screw thread while SketchUp hasn't a chance of this (at
> least, not the version 4 I choose to stay with), but the idea is to quickly
> aid visualisation, not to substitute for reality.
>
I use DesignCAD 3D for that. Ten bucks at a liquidator. Mostly because
it can read in AutoCAD files.
Lostgallifreyan
news:7dbvjkF...@mid.individual.net:
> I use DesignCAD 3D for that. Ten bucks at a liquidator. Mostly because
> it can read in AutoCAD files.
>
Ah, but Ghost lets me retain a known working OS config, recalled at will, and
an INTENSELY useful side effect of this is infinitely renewable demo periods.
:)
Joerg
> Joerg <inv...@invalid.invalid> wrote in
> news:7dbtfqF...@mid.individual.net:
>
>> Lostgallifreyan wrote:
>>> Joerg <inv...@invalid.invalid> wrote in
>>> news:7dbrk7F...@mid.individual.net:
>>>
>>>> Thanks, by now I've seen it. But the model presented ain't much to
>>>> write home about, IMHO.
>>>>
>>>>
>>> I read somewhere that it was a better version of an earlier one in a
>>> Pspice library. How good does it have to be? ...
>>
>> That depends on you. If you want the sims to model all the way to
>> failure modes I'd really be surprised if PSPICE had something in a
>> library that would even come close. My PSPICE license is too old so I
>> wouldn't know. But that would be one tough job.
>>
>> Again, a laser diode is not a linear device when you look at lasing
>> output. Not at all.
>
> No, but I'm looking at electrical INput..
>
That's the easy part :-)
BTW, I do not understand why EDN placed the SPICE list as a graphic.
Somehow that doesn't leave a very professional taste.
>>
>>> ... No point in modelling more detail than
>>> needed as a starting point. We don't even HAVE that much, any of us
>>> hobbyists and small scale designers. If experts raise their hands in
>>> horror saying there's no point in simple modelling rather than too much
>>> detail (with which Intusoft, who really know this stuff, would solidly
>>> disagree), ...
>>
>> Let them disagree. Will they pay for your dead laser diodes?
>>
>
> No, but they DO take my point when I tell them that SpiceMod shouldn't cost a
> personal user more than a very few of them. :)
>
The ones I dealt with last were about $1200 a pop. Lots of them. The
client would have been very p....d if I had blown some.
>>> ... then we'll all
>>> continue to have nothing to go on except dead laser diodes! Surely
>>> someone who knows how might change this?
>>
>> All I am saying is that I believe it is impossible to correctly model a
>> laser diode by trying to find electrical equivalents for all its
>> behaviors. You need a behavioral model in addition. All it takes for a
>> LD to die is optical overload inside the cavity. A brief wiggle of a
>> fiber connector, a spike of a few usec ... poof. The EDN model isn't
>> helping you with that.
>>
>
> Well, Tim G at Intusoft kindly said if I sent him some model numbers, he'd
> see what he can do. I sent him 5 data sheets. :) Got to try my luck, no?
> Besides, they might give a workable average for the kinds of high power red
> single mode diodes hobbyists are using.
>
> From what I've seen of my dead diodes, they are still electrically very
> similar to live ones so I'm not concerned with advanced optical modelling.
Often you can still use them as LEDs :-)
What killed them?
Joerg
:-)
I don't do that. IMHO it's quite borderline from an ethics POV to fool
demo SW into a fresh time period. Then I either buy it or move on.
Lostgallifreyan
news:7dc01uF...@mid.individual.net:
> Lostgallifreyan wrote:
>> Joerg <inv...@invalid.invalid> wrote in
>> news:7dbvjkF...@mid.individual.net:
>>
>>> I use DesignCAD 3D for that. Ten bucks at a liquidator. Mostly because
>>> it can read in AutoCAD files.
>>>
>>
>> Ah, but Ghost lets me retain a known working OS config, recalled at
>> will, and an INTENSELY useful side effect of this is infinitely
>> renewable demo periods.
>> :)
>
>
>:-)
>
> I don't do that. IMHO it's quite borderline from an ethics POV to fool
> demo SW into a fresh time period. Then I either buy it or move on.
>
That's what I usually do (and I make a poing of buying from small firms or
good individual programmers rather than big firms, with special emphasis on
paying for tools written by coders who value writing for ALL of Win32).
The only reason I don't use the freeware Sketchup version 5 is it won't run
on W9X like the old demo v4 does. I really dislike Windows XP.
Joerg
Ringing? I never had that. Don't drive them through a built-in inductor :-)
LDs are usually current driven. The prudent way is to impose a constant
DC current, very well stabilized and equipped with belts, suspenders,
cushions, airbags. Then the fast signals are fed in via a current
"robbing" shunt circuit to ground. That pretty much makes sure you can't
fry it.
Lostgallifreyan
news:7dbvr6F...@mid.individual.net:
>>> Again, a laser diode is not a linear device when you look at lasing
>>> output. Not at all.
>>
>> No, but I'm looking at electrical INput..
>>
>
> That's the easy part :-)
>
Precisely. I hope. If a decent electrical model isn't enough then we all have
to think further, but most of us haven't even got that much yet. We'd save a
LOT of resources if we did.
> BTW, I do not understand why EDN placed the SPICE list as a graphic.
> Somehow that doesn't leave a very professional taste.
>
I wondered about that too. They let registered users on their site download a
text list for free though. I think maybe they just want to lead the horse to
enough water to improve the chances it will drink theirs. Anyway, I copied it
out by hand and posted it earlier..
>>> Let them disagree. Will they pay for your dead laser diodes?
>>>
>>
>> No, but they DO take my point when I tell them that SpiceMod shouldn't
>> cost a personal user more than a very few of them. :)
>>
>
> The ones I dealt with last were about $1200 a pop. Lots of them. The
> client would have been very p....d if I had blown some.
>
I bet it would still hurt them less than the ten diodes I bought for �520
when my weekly income was about �75, when I killed four of them just trying
to prove to people the existence of death by retroflection (and not by ESD as
was claimed) when the sellers and makers refused to accept what is now
generally KNOWN. And no, they did NOT reimburse!
>> From what I've seen of my dead diodes, they are still electrically very
>> similar to live ones so I'm not concerned with advanced optical
>> modelling.
>
>
> Often you can still use them as LEDs :-)
>
Exactly. That weird fact is why I think it's valid to consider meaningful
separation between their full behaviour and their electrical behaviour.
> What killed them?
>
Mostly retroreflection as described above, and also deliberate brinksmanship
when trying to find the optimum compromise between a short blazing fun life,
and a long boring stable one. :)
Lostgallifreyan
news:7dc0a0F...@mid.individual.net:
> Ringing? I never had that. Don't drive them through a built-in inductor :-)
>
Not intentional.. I'm using an LM317. Yes, I know it's not the approved way.
It WORKS, far better than expected, and most people who explore weird tricks
with an LM317 are mightily impressed with it, from the guy who built a class
A headphone amp, or the radio ham who built a transmitter round one...
My physical circuit build, AND the later spice modelling, both indicate that
an LM317 for a cheap way to get up to an amp-amd-a-half of DC coupled
proportional laser drive at up to 500 KHz is very likely to work well. Maybe
the inductance is in the LM317 model, I don't know where else it can be in my
simple circuit models. What's crucial is that it is the SAME overshoot I saw
in the real circuit so spice is already telling me good things, and I've
already improved the driver on the strength of that spice model.
> LDs are usually current driven. The prudent way is to impose a constant
> DC current, very well stabilized and equipped with belts, suspenders,
> cushions, airbags. Then the fast signals are fed in via a current
> "robbing" shunt circuit to ground. That pretty much makes sure you can't
> fry it.
>
Definitely true. Shunting is my favourite method, and I might return to it
with this current indea. But half the fun is trying to see how well I can
push this LM317 idea. I've seen circuits that are 'better' that don't seem
either much better or worse than mine, which also happens to be very polite
at startup, no spikes at that moment at all..
Phil Hobbs
resistors required.)
Phil Hobbs
> Joerg <inv...@invalid.invalid> wrote in
> news:7dc0a0F...@mid.individual.net:
>
>> Ringing? I never had that. Don't drive them through a built-in inductor :-)
>>
>
> Not intentional.. I'm using an LM317. Yes, I know it's not the approved way.
> It WORKS, far better than expected, and most people who explore weird tricks
> with an LM317 are mightily impressed with it, from the guy who built a class
> A headphone amp, or the radio ham who built a transmitter round one...
>
> My physical circuit build, AND the later spice modelling, both indicate that
> an LM317 for a cheap way to get up to an amp-amd-a-half of DC coupled
> proportional laser drive at up to 500 KHz is very likely to work well. Maybe
> the inductance is in the LM317 model, I don't know where else it can be in my
> simple circuit models. What's crucial is that it is the SAME overshoot I saw
> in the real circuit so spice is already telling me good things, and I've
> already improved the driver on the strength of that spice model.
Ohhhhhh..... You're using a voltage driver, and trying to trick it into
being a current driver. Bad, bad, bad, bad news.
Due to the rolloff in the loop gain, the output of a voltage regulator
appears inductive, which will reliably give you a big noise peak if the
output cap is too big, and some ringing if it's too small. 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.
Cheers,
Phil Hobbs
Joel Koltner
news:xoidnU2-iIbBSu3X...@supernews.com...
> Ohhhhhh..... You're using a voltage driver, and trying to trick it into
> being a current driver. Bad, bad, bad, bad news.
I tried to use an LM317 as a constant current driver for a regular old LED (a
high-power white LED -- needed a few watts; this was >5 years ago when white
LEDs were still new and spendy) and it just sat there and oscillated on me.
You do see people suggesting using LM317s (or similar) as constant current
sources all the time, though... when can it work? It sounds like you're
saying it's almost always a bad idea?
> 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.
Compared to an LM317 though, isn't the main difference that the LM317
essentially has Power->drive transistor->LED->sense resistor whereas Joerg's
approach is Power->LED->drive transistor->sense resistor? ...so you're
essentially isolating the current sensing from the load itself, to some
degree?
---Joel
Lostgallifreyan
iIbBSu3XnZ2d...@supernews.com:
> Ohhhhhh..... You're using a voltage driver, and trying to trick it into
> being a current driver. Bad, bad, bad, bad news.
>
I thought if constant current config for an LM317 is good enough for the
standard data sheet then it's good enough for me. :) (And if you look at
the LaserFAQ closely you'll also see that it's good enough for Winfield
Hill, though he wasn't trying to modulate it..) Like I said, part of the fun
is in making the LM317 do weird and wonderful things. It's fun to know that
wherever you have some, you can do some amazing things normally done with
other parts, usually exotic, more costly, with MUCH more complex board
layouts, etc..
> Due to the rolloff in the loop gain, the output of a voltage regulator
> appears inductive, which will reliably give you a big noise peak if the
> output cap is too big, and some ringing if it's too small.
That fits what I see. I've managed to tame it to something respectful. I
think an 'overshoot' that results in a minimum-to-maximum deviation of
about 3 mA along the 'flat' top of a 500 KHz square wave at 160 mA isn't bad.
People who know a lot more than I do have been content with worse.
> 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).
Lostgallifreyan
> snivet
�Qu�?
Lostgallifreyan
news:_W4cm.439882$Lo1.3...@en-nntp-04.dc1.easynews.com:
> I tried to use an LM317 as a constant current driver for a regular old
> LED (a high-power white LED -- needed a few watts; this was >5 years ago
> when white LEDs were still new and spendy) and it just sat there and
> oscillated on me.
>
Never seen that, though I know it HAS been seen, the guy who built a
transmitter round an LM317 did so to explore it. I use an LED lamp fopr my
main room light when I'm at the compiter, it uses an LM317 with a voltage
reference and a pot to dupe it to work as a dimmer. It's not very efficient
but it doesn't flicker either like most power converters do, and it's much
cheaper. Solid as a rock.
> You do see people suggesting using LM317s (or similar) as constant
> current sources all the time, though... when can it work? It sounds
> like you're saying it's almost always a bad idea?
>
I tend to trust manufacturers data sheets. It beats assuming they're useless.
:)
Vladimir Vassilevsky
Phil Hobbs wrote:
The high speed LD drivers I've seen used the differential amp topology.
The LD was the load in one of the shoulders; the max. current was set at
the tail. For the faster switching, when the LD is in the "off" state,
it was kept at the bias current little below the threshold of lasing.
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.
Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com
Lostgallifreyan
3XnZ2dnUV...@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?
Vladimir Vassilevsky
Lostgallifreyan wrote:
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.
Lostgallifreyan
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.
George Herold
> Lostgallifreyan wrote:
> > 5ZRI-3XnZ2dnUVZ_vKdn...@supernews.com:
>
> - Show quoted text -
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.
But I'm mostly interested in how the current modualtes the wavlength.
Which as Phil H. said has all sorts of different time scales. The 785
nm LD's I use have a relaxation oscillation frequency of 6+GHz!
I have no idea about spice models.
George H.
Lostgallifreyan
bf5874...@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.
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...
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.
In other news, I seem to have dropped alt.lasers from the cross-post list.
Annoying. :)
Lostgallifreyan
news:Xns9C581C5A324...@216.196.109.145:
> In other news, I seem to have dropped alt.lasers from the cross-post list.
> Annoying. :)
>
By which I mean, it should have been there too.
*sleeps*
George Herold
> George Herold <ggher...@gmail.com> wrote in news:379c1689-21a2-456e-9d3b-
> bf5874b7f...@2g2000prl.googlegroups.com:
Yeah, there are lots of copies of the H&L laser diode current driver
on the web. Start with a simple current source (opamp, pass element
(FET) and sense resistor) and then add a second 'tap' into the laser
diode. A resistor works just fine. H&L add two taps. One is op-amp
based and works up to a few MHz and then a 50 ohm resistor for HF
modulation.
George H.
George Herold
> George Herold <ggher...@gmail.com> wrote in news:379c1689-21a2-456e-9d3b-
> bf5874b7f...@2g2000prl.googlegroups.com:
>
Yeah, there are lots of copies of the H&L laser diode current driver
Phil Hobbs
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.
Phil Hobbs
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.
Phil Hobbs
That works great too, and is superior if you need to turn the lasing on
and off without going too far below threshold. The key is that there's
almost no swing at the emitters (especially if you drive them
differentially), so you don't suffer from the poor HF response of the
current source--you can put a choke in series and forget about it.
I'm usually doing something fancy with AC modulation of a CW diode, e.g.
modulation-generated carrier, so the swing is even smaller.
Phil Hobbs
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.
Tim Williams
news:Xns9C585A893...@216.196.109.145...
Wow, I didn't know people were still using that term. Last time I heard it
was in talking about tube televisions from the 1960s!
Snivets is where the sweep output tube undergoes oscillations (Barkhausen
oscillation) between the plate and screen, when plate voltage is lower than
screen (Vp(sat) typ. 30V for these types, at Vg2 = 125V). It's supposed to
make an electron-beam-driven resonant cavity, producing UHF oscillations
something like a klystron I suppose. The solution is to raise the voltage
on the beam former grid to about 30V.
Can I get a modern definition for "snivets"?
Tim
--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
John Larkin
wrote:
>Lostgallifreyan wrote:
>> Joerg <inv...@invalid.invalid> wrote in
>> news:7dbdd3F...@mid.individual.net:
>>
>>> Lostgallifreyan wrote:
>>>> If anyone is following this and wants to try modelling their own stuff,
>>>> I found what might be a way.
>>>> Intusoft make a tool called SpiceMod which is part of a package they
>>>> call ICAP4 though it seems the demo setup doesn't have that tool, just
>>>> some very good noted on it, and modelling in general:
>>>> The file WkwModels.pdf from the demo install answers a lot fo the
>>>> questions I had about modelling diodes, which parameters to tweak, and
>>>> extraction from data sheets.
>>>>
>>>> I don't know if the lack of response to me is because of a thousand
>>>> experts silently screming RTFM at me, or because it's actually
>>>> asomething they DON'T KNOW. Given that Intusoft explain that this is a
>>>> serious challenge for experts too, I'm assuming maybe they really don't
>>>> know, so they might benefit from that file as much as I will.
>>>
>>> Most of us just use a regular diode to simulate because all one
>>> (usually) wants to know is that there definitely won't be any ever so
>>> slight spike in diode current because LDs can go poof in microseconds.
>>> Simulating the optics part would be a major challenge, I think.
>>>
>>
>> Thought that might provoke an expert. :) I agree, same here, that's all I
>> usually need too, though like that EDN manual says, a more detailed model
>> that allows models to give warning of imminent demise is useful. Modelling
>> for ESD is likely daft, better that we just take care and put in TVS's and
>> such, but when it comes to fast modulation, a model definitely helps. Surely
>> you'd have a use for that, no?
>>
>
>I have designed LD circuitry but I am not an expert. Senor Hobbs would
>be one. TVS don't work well. Their cutoff isn't terribly well defined
>and they have too much capacitance for this. Just handle the things with
>care. I've never killed one with ESD, knock on wood ;-)
>
>
>> 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?
John
Joerg
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.
Joerg
> George Herold <gghe...@gmail.com> wrote in news:379c1689-21a2-456e-9d3b-
> bf5874...@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.
Joel Koltner
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
news:7dduinF...@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
news:Ticcm.95224$Qg6....@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
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
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.
Joerg
10MHz is sluggishly slow for a decent laser diode.
Lostgallifreyan
news:7ddv8fF...@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
> Lostgallifreyan wrote:
>> Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote in
>> news:xoidnU2- iIbBSu3XnZ2d...@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
> On Wed, 29 Jul 2009 12:32:03 -0700, Joerg <inv...@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.
Joerg
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 :-)
Lostgallifreyan
> 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
wrote:
>John Larkin wrote:
>> On Wed, 29 Jul 2009 12:32:03 -0700, Joerg <inv...@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
news:M3kcm.493202$6p1.2...@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
news:7de22pF...@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
news:7de27aF...@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
news:7de2obF...@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
> Joerg <inv...@invalid.invalid> wrote in
> news:7de2obF...@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 :-)
Lostgallifreyan
news:7de4n6F...@mid.individual.net:
> Lostgallifreyan wrote:
>> Joerg <inv...@invalid.invalid> wrote in
>> news:7de2obF...@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
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.
Joel Koltner
> If you always do everything the 'right' way, how are you going to learn
> anything for yourself?
I don't really see a connection there. Certainly there's plenty to be learned
from applying ICs such as the LM317 in unorthodox ways, but there's also
plenty to be learned from studying the "right" way to solve a specific
problem. Indeed, often the "new" right way comes about from someone
experimenting with the old ways and having a flash of insight.
I'm all for people experimenting and figuring out interesting new applications
for circuits originally designed for different applications, but I'm also all
for examining the works of the likes of Phil and Joerg and Jim since they have
a demonstrated track record of building rock-solid designs.
In a hobbyist environment, one should certainly try out whatever wild ideas
pop into their heads. In a work environment, while engineerins shouldn't
generally be discouraged from trying out wild ideas :-), they need to be
prioritized based on the perceived risk, time/resources needed to experiment,
other project priorites, etc. I've seen firsthand someone's clever idea
costing lots of money because the idea turned out to have unforeseen
limitations -- any time you're proposing something wildly different from the
traditional approaches, be sure to budget for plenty of testing time. On the
other hand, you have John's company, where many of his products are completely
unique based on his ability (and his employees') to successfully incorporate a
few wild new ideas into viable products.
---Joel
John Larkin
wrote:
Yes. We did wind up with a reel of FR804's that snap nicely, maybe
decent PIN diode material, but we went to a bigger part in the end,
higher voltage and more power dissipation.
It was fun, but we only sold a few.
>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.
You should probably use real RF power PIN diodes, like
Skyworks/Microsemi/Aeroflex. They have doping profiles that give
absurdly long recovery times, so it takes very little DC to control a
lot of RF. I used exotica because I needed a huge amount of power
dissipation capability when we were running at 500 KHz.
John
Lostgallifreyan
> I don't really see a connection there. Certainly there's plenty to be
> learned from applying ICs such as the LM317 in unorthodox ways, but
> there's also plenty to be learned from studying the "right" way to solve
> a specific problem. Indeed, often the "new" right way comes about from
> someone experimenting with the old ways and having a flash of insight.
>
That's exactly how I improve code when I write it, I look at what aorks best
and always revisit to see if there;s a further improvement because there
often is. But there is also context. In several posts here I've accounted for
the context of my decision to try this LM317 wheeze. There's no reason not to
try it, and a few good ones to try it.
Michael A. Terrell
> >
> >> snivet
> >
> > �Qu�?
>
> Wow, I didn't know people were still using that term. Last time I heard it
> was in talking about tube televisions from the 1960s!
>
> Snivets is where the sweep output tube undergoes oscillations (Barkhausen
> oscillation) between the plate and screen, when plate voltage is lower than
> screen (Vp(sat) typ. 30V for these types, at Vg2 = 125V). It's supposed to
> make an electron-beam-driven resonant cavity, producing UHF oscillations
> something like a klystron I suppose. The solution is to raise the voltage
> on the beam former grid to about 30V.
>
> Can I get a modern definition for "snivets"?
"Sniveling Idiot". ;-)
--
You can't have a sense of humor, if you have no sense!
JosephKK
<no-...@nowhere.net> wrote:
>Lostgallifreyan <no-...@nowhere.net> wrote in
>news:Xns9C512D9705D...@216.196.109.145:
>
>> Definitely a communications breakdown spreading here but I'm not entirely
>> sure it's electro-optical in nature..
>>
>
>Does anyone here know how to adapt a diode model for a laser diode?
For an all but clueless first cut i think you would need a four
terminal device, to include the transport of emitted photons.
Lostgallifreyan
news:3e7o75h7m29qpd1ca...@4ax.com:
Yes, I was sent an Intusoft newsletter that contained just such an animal,
but it's based on a Hitachi 3mW IR diode, I think. But as a 'dead' diode with
facet damage from ESD or other surge usually behaves very similarly to a live
fresh one, electrically, AND most high power diodes have no monitor
photodiodes anyway, there's nothing wrong with only two terminals. What is
then critical, if it's to be driven hard, is to include temperature
monitoring in the model. In practise diodes will vary but the setting will be
a set-and-forget one based on a single measurement of power at maximum drive,
once the thermal compensator works. I did this once (before I ever looked
into spice) using an LM317 and some thermistors in the sense resistance
network. It sounds crude, but I calculated it in some detail, and it worked
well. Apart from that LM317, the entire driver was discrete passive parts.
(Wasn't modulated though, have to add stuff then.)