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Thread: Stan_Ham diode driver (analog)

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    Quote Originally Posted by Pangolin View Post
    Yes, I can confirm that this is the case. It is quite amazing that you can "see it" since ESD events last only a tiny amount of time. Even once the laser diode has been destroyed by a first strike of ESD which causes a dead short across the terminals, further ESD evens will still give light output (remember we are talking about 50 amps here...)
    50 amps? Say what? I though ESD was high voltage / low current.

  3. #43

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    Volts push current through resistance. So HV can push lots of amps for a short time through a low resistance. Static is usually considered as a low current form because it's usually found associated with insulators and other conditions of high resistance. Once it collects on any plate of metal, the current can be huge when it discharges.

    Bill, I agree, zeners don't seem right to me, but that's what he said when I wanted to use varistors. He made something work right, whatever he did with zeners. (I don't know what his background is but he's in full time work, I think as an electronics designer).

    Re balls to zap diodes, I do it every time I test a new design. Not always the diode directly, but any part of the case and diode mount that can be touched by a finger will be zapped by a 6 to 10 cm spark because I don't trust it till I know it can take it. "The proof of the pudding..."

    Re short flashes, apparently a human eye can resolve a single photon. I don't remember where I read that, or know if it's true, but it wasn't some flip remark on the Interweb, it was part of something erudite. So if several of them arrive at once, we'll see them (maybe more amazing is that a multiplexed camera CCD also saw them, I'd have thought there was a good chance it wasn't picking up signals at the instant of the flash, though I think what actually happened is his filtering broadened what was left of a clipped peak, so the flash duration might be a few microseconds or more). Robin's diode wasn't crippled, it worked normally when powered up later, collimated beam at same strength as before. I think Dave's right, the mod input was zapped rather than the diode itself.


    EDIT: Bill, got to play devil's advocate on this for a moment.. you mention a 5 mm shorting braid only having 50/50 chance of protecting a diode, so with the Lasorb, the limiting factor might be the wired connection to the diode circuit. I never looked into details of solder's resistance, but I have to wonder if special precautions are needed to prevent a joint from being inadequate even if it looks perfect and even tests perfect on any meter we ordinary mortals can afford.
    Last edited by The_Doctor; 01-20-2009 at 06:51.

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    Quote Originally Posted by The_Doctor View Post
    Re short flashes, apparently a human eye can resolve a single photon. I don't remember where I read that, or know if it's true, but it wasn't some flip remark on the Interweb, it was part of something erudite.
    There is a paragraph or two about this in the Laser FAQ. Evidently the rods in the eye can respond to a single photon, but it takes more than one rod firing to trigger the sensation of light in the brain. So it might be that you need 2 or 3 photons to actually "see" a flash, even though the eye could in principle detect a single photon.

    Adam

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    Human body model is 100 pF discharged through 1500 ohms non inductive , charged to x Kv, usually 7 or so. The spec says the test instrument can discharge in 25 nanosconds or less.

    There is also the machine model and the charged device model (nasty) for handling parts on conveyor lines etc

    http://www.esda.org/basics/part5.cfm

    I want to try lasorb asap, I just touched a Maxys module case day before yesterday and popped the diode with static. The video of of the wave lumia is now a 250$ video, for the spare Maxys used for filming ran for a whole 10 minutes since it got here.

    Steve
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    The paper in question calls it 7 photons per second per retinal cell, with several cells firing. I'd say that is down in the noise, even in a so called totally dark room. Very optimistic number.

    Steve

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    Quote Originally Posted by buffo View Post
    There is a paragraph or two about this in the Laser FAQ.
    There you go! I knew it was something erudite. Re multiple photons, I guess the brain could have picked up a one-photon trigger from an eye, but as Steve says, it's right into noise floor levels so why bother? It probably developed on the same basis that a venus fly trap can only close on the second hair trigger within a certain time and with strength consistent with the first. It's expensive to respond to false positives..

    Steve, ouch. Static wasn't the worst for me though, I was paying 50 a throw for Opnext/Hitachi 80 mW diodes at one point (and that was a set of ten at once to economise) and at said point discovered that they died WAY too easily. I discovered retroreflection death. And I do mean discovered. At the time I had no precedent for it, the seller, and even the maker, admitted nothing, and I didn't know what to look for online or who to ask then. The seller was helpful actually, took it up with the maker on his next visit to Japan, but no liability was accepted, or even an admission given that the phenomenon exists. As repeatability is GOD in science, I killed 5 diodes just proving beyond doubt that my static precautions were good, and not responsible (this was when I started zapping sparks at the mountings), and that even a crude dirty bathroom mirror can kill a diode every time, let alone a clean 99.99% broadband dielectric. Funny how violet diodes are immune. Got to be something the makers of reds can learn from there...

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    Its been my experience that everything blue and uv led have a more SCR like structure in their behavior, and and a very fast response to changes in bias.

    Steve

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    Quote Originally Posted by dave View Post

    AHA. Shocking external to the driver is not the same as shocking the laser diode itself!

    One thing to remember. It wasn't our sole intention -- going into this -- to invent and ESD protector for laser diodes. It was our intention to create a really great laser diode driver. Up until now, I haven't seen even so much as a single one I liked... So for us, "step 1" in creating a great driver was to see how to protect the laser diode. We reviewed everything that everyone had done up until now and, surprisingly, nobody else even got past what we defined as "step 1" successfully! So we created something that successfully achieves "step 1". Instead of hoarding the technology, we decided to share it (although I am sure people will bemoan us selling it). But at around $1 profit per device, I hope people see that if we sell one of these to every single Pangolin user, we will have only made $10,000...

    Just wait 'til you see what we do for "step 2" .



    Quote Originally Posted by The_Doctor View Post
    Bill, I agree, zeners don't seem right to me, but that's what he said when I wanted to use varistors. He made something work right, whatever he did with zeners.
    For mere "external signal" protection, it could very well be that the system would survive with no protection what so ever. The ESD only lasts for a few tens of nanoseconds -- not enough to propagate very far into a circuit that has relatively low bandwidth. But unlike the op amps, filter circuits and, for that matter, power transistor that drives the diode, which could not possibly react within one nanosecond let alone tens of nanoseconds, a laser diode actually can react that fast. That's where the challenge lies.

    Quote Originally Posted by The_Doctor View Post
    Re balls to zap diodes, I do it every time I test a new design.
    Diodes?


    Quote Originally Posted by The_Doctor View Post
    Not always the diode directly
    Hehe. Didn't think so .



    Quote Originally Posted by The_Doctor View Post
    EDIT: Bill, got to play devil's advocate on this for a moment.. you mention a 5 mm shorting braid only having 50/50 chance of protecting a diode, so with the Lasorb, the limiting factor might be the wired connection to the diode circuit.
    I am pretty sure that, on the web site, we mention that LASORB should be placed as close as possible to the laser diode, and that ANY ESD protection means must be closer than 5cm round trip, from the laser diode.

    In any event, the 5cm copper braid experiment has nothing to do with solder. Again, it's all just simple math. (I find myself saying that a lot lately...) In order for an ESD protection scheme to be successful, the impedance must be less than 50 milliohms from 20 MHz through 1GHz. The inductance of the copper braid is the killer... Also, we used copper braid instead of just a piece of copper wire to prove that it we have given "skin effect" every possible chance of having the benefit.

    LASORB is better -- much better in fact, than a 5cm copper braid.

    Bill

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    So when are you going to give us a hint, on how this widget works, I note your application is not showing at the patent server yet. That in and of itself is s not unusual, I know it can take years for application to show up on the server.

    Steve

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