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Thread: Stan_Ham diode driver (analog)

  1. #61
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    Quote Originally Posted by FourDee View Post
    I know this is a bit off topic, but I've been thinking about most current driver designs, and they all make it hard to use case negative diodes

    I've drawn up some quick schematics of the basic design of most diode drivers and the one I am proposing.

    Does anyone see any reason why this setup would not work or be worse than the original one

    (I basically just moved the sense resistor and implemented a difference amp ...)
    I think that could work. I used a differential amp in my first (and so far, only) test of a diode driver with proportional modulation. It controlled an LM317 though. It gets clean square waves at 50 KHz with better shapes than Robin Bowden's Die4drive does at 100 KHz (and with no overshoot), but I don't yet know if they're also better at 100 KHz, they likely won't be. But either way, your circuit and mine both have a diff amp and a current sense resistor on the high side of a negative-can diode, so I think yours will work too.

  2. #62
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    Quote Originally Posted by keeperx View Post
    Hey.. back to the original topic...
    did anyone ever post the original dual driver board?
    i think they are ontopic.,. discussing ESD protection for driver circuits

  3. #63
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    Some time ago i was looking for a simple driver for analog modulation of cheap opencan reds and bleurays.
    Rob stanwax emailed me with a driverschematic of his dualdriver he was using in his small projector.
    with some help of Rob (Laserwave.co.uk) i modified the driver and made a single anolog board out of it.
    im looking for the original driver
    Quis custodiet ipsos custodies?
    Solid State Builders Group

  4. #64
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    Quote Originally Posted by keeperx View Post
    im looking for the original driver
    contact ROB.

    i'm not at "liberty" to give out that schematic/pcb..
    Sorry

  5. #65
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    Quote Originally Posted by The_Doctor View Post
    Ok. That was what I was getting at, the lead length, as well as the solder itself. People tend not to solder parts very close to their wire entry points for fear of damage, so you'll have to have specific advice about this or people might leave leads long enough to cause bother.
    Well, in an app note or so, we will have to say "as closely as possible or practical" or use some such wording. But it doesn't mean it has to be so close that it will damage the part from heat transfer. At 5cm you are 50-50. Probably 2cm would do the trick. It doesn't have to be so close you can shave your face with it .



    Quote Originally Posted by The_Doctor View Post
    A lot of people profit without having to play the patent system every time they think they have a bright idea. Most people who make a profit probably have no idea how the patent system works, but they don't let it stop them because they spend time producing and optimising work rather than aggressively and systematically defending every new idea they have about it.
    Agreed. If you take a look at the "continual innovation" page, which of course shows only a very abbreviated version of our work, you will see that on that entire page, only three things have been patented. The rest work as you say -- optimization, etc. We only patent if a) we want to make sure that WE!! have access to a technology (along with others), or b) we have something that is realy really really unique.

    (For the things that are only really really unique, we don't patent .)




    Quote Originally Posted by The_Doctor View Post
    What did you think retroreflection testing involved, given that no-one I could reach at that time was admitting a problem existed?
    Gosh I just must have missed that one. But if you have questions about the physics of lasers (I mean semiconductor physics), we have a wonderful consultant we could turn you onto, which was a consultant on the LASORB project. Brilliant woman!!



    Quote Originally Posted by The_Doctor View Post
    Assuming an SCR is used with fast rise time being the trigger (via capacitative coupling to the gate), then arbitrary laser diode Vf can be protected, as all will be way below the SCR anode breakdown voltage, but if this is it, how to turn off the SCR later in a powered CW circuit?
    Hehe. Magic .


    Quote Originally Posted by The_Doctor View Post
    One way seems to be a tiny capacitance arranged (and charged by the ESD event itself, perhaps)
    Perhaps .


    Quote Originally Posted by The_Doctor View Post
    For the reverse bias shunting, the Lasorb pages mention a 'zener' of sorts, but why not just an ultrafast rectifier? Not Schottky, just very fast. Clamping at 1V or so should be ok for a laser diode in reverse, I saw a max of 2V specified for the Rohm diodes, for example. The diodes I used last recover in 25 ns in either direction, and no doubt better can be found now.
    The words of my old university professor come to mind: "Student teach thyself"!

    All good questions. Now all you need is six months, a lot of experimentation with components from a wide variety of vendors, a 10GHz sampling scope to verify that you are doing everything correctly, a a few ESD guns at around 8K each and you'd have it. Or you could spend a few bucks on a LASORB...

    Bill

  6. #66
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    Got to admit, I'll take the Lasorb. At least ten of them, like as not. They'll be more fun than messing with low ESR tantalum and all the rest. While I contest that you don't need that much dough to test stuff (I can make ESD with my socks), there's no arguing that it takes a lot of time to try enough things to build up a realistic picture of the whole system performance if you haven't got the best gear. One reason I don't make much is I like to try lots of things. Like you say, it takes time.

    Re your consultant, I'll try to remember, thankyou. I might need to ask at times. The LaserFAQ and Google get me sorted most times, but there might be times when a direct question to a knowledgable person helps best. Though I tend to like to teach myself, literally. I find that if I don't figure out enough to ask decent questions, I probably won't understand the answers. And if I do figure it out, the main obstacle to wading through Google results isn't the weight of returns (so long as I'm awake and patient enough), it's the fact that so many of the important ones seem locked away in paid-access resources. Like Steve (Roberts) recently said, he couldn't get at something he used to take for granted in a universtity system. That might be when I might call for that help. But only if I've done all I can first.


    Re that cap and SCR idea, I also got that from some other wheeze of mine. It was a slow system though, I wanted an LED switched on and off with one nonlatching button and extremely few components for a 'bombproof' LED flashlight idea I had some years back. The industry long since went beyond what I could do, but I did manage the switch, it was nonlatching in usual timings of user operation, but if you nudged it sharply a cap stored a charge, passed it to another cap, and on release, the charge triggered the gate, latching the SCR to keep the LED on. Longer nudges let that cap discharge so fast nonlatching worked too. Timing was critical, as was the quality of the switch, and better ways exist. Still nice though, it consumed zero current when off, unlike most schemes. Nothing to do with the subject here, but it was enough to make me think about SCR triggering, but didn't help me figure out the unlatching. Maybe it will, maybe it won't....

  7. #67
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    Warning , threadjack:
    Warning, Electrical Engineering attempt at Humor follows:

    Quote


    Gosh I just must have missed that one. But if you have questions about the physics of lasers (I mean semiconductor physics), we have a wonderful consultant we could turn you onto, which was a consultant on the LASORB project. Brilliant woman!!
    end quote

    Oh, gawd, Bill Benner reads Britney's Guide to Semiconductor Physics.....


    http://britneyspears.ac/lasers.htm

    Sorry Bill , I could not resist.


    Or the nice lady Professor from Columbia that just took half the LD manufacturers to the cleaners.....?

    end Threadjack:

    Steve
    Last edited by mixedgas; 01-21-2009 at 13:08.

  8. #68
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    Quote Originally Posted by mixedgas View Post
    Crowbars are interesting. Assuming an SCR is used with fast rise time being the trigger (via capacitative coupling to the gate

    end quote

    I just had a sensitive gate SCR on a curve tracer this morning, its fast, but not that fast. Tq for a fast inverter SCR is 20 uS, for a normal one it is 100 uS and that is anode current dependent. Great for crowbars where Di/Dt is not so critial, but a stock scr is not fast enough to shunt a 25 nanosecond pulse. Or am I wrong?

    On the other hand, a designed for speed SCR might be:

    http://www.littelfuse.com/data/en/Ap...tes/an9708.pdf

    Steve
    Yep, that firm cropped up during my hour or two online with Google earlier. But as far as I can tell, the action of two transistors chosen for speed and reinforcing each other in turn-on will rise faster than most if not all dedicated SCR's. Actually, that might be a clue to the unlatching mechanism too.
    Ò^O
    (I seriously wish I could raise one eyebrow at times, but that is as close as I'll ever get).


    Edit. That Britney Spears thing makes me want to raise the other one. I've encountered her before, and she goes way over my head.

  9. #69
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    Quote Originally Posted by mixedgas View Post
    Lambda Diode.
    Oh man, 'negative resistance'! At this point I need to put my seething neurons to bed.

  10. #70
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    Quote Originally Posted by The_Doctor View Post
    I think that could work. I used a differential amp in my first (and so far, only) test of a diode driver with proportional modulation. It controlled an LM317 though. It gets clean square waves at 50 KHz with better shapes than Robin Bowden's Die4drive does at 100 KHz (and with no overshoot), but I don't yet know if they're also better at 100 KHz, they likely won't be. But either way, your circuit and mine both have a diff amp and a current sense resistor on the high side of a negative-can diode, so I think yours will work too.
    So why doesn't anyone use this kind of driver?

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