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Thread: Bizarre simpledrive II driver problem

  1. #11
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    Here's an idea to solve this forever. Load switching. Make a circuit that hooks to a dummy load and switches over to the diode after a few seconds. This then absorbs spikes. Do the same on turn off. Thinking a dpdt on off switch. One side is power and the other is the switch circuit. One shot 555 and 4066? Then again zener can lock voltage. Is there a currrent version of a mov? I'm sure this can be engineered out.

  2. #12
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    Quote Originally Posted by jors View Post
    Do you power with Lab PSU while adjusting? Which brand is your PJ PSU? I got 4 P73 killed by a chinese 'no brand' PSU months before...now all seems OK with Meanwell
    I set-up with a lab supply. The supply in the projector is a meanwell. Although, to be honest, I have had a few meanwell's go up in smoke in LED installations. Not sure if they were genuine meanwell? They were very sparse and cheaply built when I opened the ones that failed.

    Quote Originally Posted by kecked View Post
    Here's an idea to solve this forever. Load switching. Make a circuit that hooks to a dummy load and switches over to the diode after a few seconds. This then absorbs spikes. Do the same on turn off. Thinking a dpdt on off switch. One side is power and the other is the switch circuit. One shot 555 and 4066? Then again zener can lock voltage. Is there a currrent version of a mov? I'm sure this can be engineered out.
    I'm thinking an easier solution may me to add a low inductance resistor in series with the diode. Say the power supply = 15V and the Vf of 2 series blue LDs is ~10v. A momentary short on the driver transistor would put a max of 5V on the resistor (plus the drivers sense resistor). A 1ohm resistor would allow only 5amps to flow. Probably not enough to kill the diodes on a start transient.
    Last edited by logsquared; 07-10-2017 at 08:47.

  3. #13
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    If this is the project I'm thinking of, I've got the other 10 drivers of the batch in a pair of projectors (used them this weekend just gone actually, still working fine)
    Although they did have a bit of leakage last year where I had to adjust the quiescent current (perhaps you recall the conversation BBE)
    http://www.facebook.com/SubsonicSystems
    http://www.frikkinlazors.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  4. #14

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    99% we are dealing with some defective part. Unfortunately, I can not remotely check this ...

    My offer for replacement is still in force. This fall, I launch new drivers for lasershow, I can send you the first of them as a replacement

  5. #15
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    How about a picofuse. Might pop a bunch but diodes will live. Add lasorb for voltage spikes. Then your covered for current and voltage. Maybe add a current shunt in front of the driver. So the driver can't ask for more than you set the max even if the driver fails entirely. I think a resistor might work but It would get hot. Thinking a transistor or get of some kind. Sort of a driver on the driver.

  6. #16

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    It's all a workaround. A good driver should not kill diodes.

    In most cases, laser diodes do not die due to a current spike, but because of the reverse current spike, generated by self-inductance in the wires. In this situation, only the Schottky diode or lasorb on diode side can help

  7. #17
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    ... how fast have your drivers to be?

    For a forums-project I'm building high current drivers with up to 9 Amps current and some ten to hundred Kilohertz bandwith.

    Here's a graph from one of my older prototypes with LM338 IC's used for constant current driving - tree parallelized LM338 gives this switching curves at 6,5 Amps current (measured across a 0,1 Ohm-resistor) without any over- oder under-oszillation

    Pulsform mit 3x LM338-KSQ-Treibern.png


    Viktor

  8. #18

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    How fast should it be for laserist needs? The prototype of what I will offer has about 250ns rise / fall responce at ~5A. But this is too fast for regular use and imposes certain restrictions on the feeder line between the driver and the diode. That "wiring" which I often see on the forum, is categorically contraindicated at this speed ))
    Attached Images Attached Images

  9. #19
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    ... the needed speed depends mostly on your application - with laser-engraving or cutting on an XY-plotter-style machine (most laser-cutters are) rising/falling times of some ten Microseconds are more than enough ... but with the actual development with an XY-galvo-scanner it's more like some ten Nanoseconds -- especially with adjustable pulse-widths for "colour-marking" - here I'm dealing with pulse times between 400ns down to 10ns!

    Viktor

  10. #20

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    Just look at the wiring of any projector in this forum and try using a driver with 200-400ns feedback in these projectors, haha. At best, you will get a RF/noise transmitter, at worst - a burnt diode. For laser shows (in my option), it does not make sense to use the driver with rise/fall faster than 1us. Also need to pay attention to the modulation signal waveform after ~10-20 meters of ILDA cable, it never happens superb.

    And another question, if I may ask you:
    please explain the nonlinearity of the signal rise on your waveform (1);
    can you show this (2) part of the waveform, say, in 1us resolution? As a rule, all the oscillations are in this section )
    Attached Images Attached Images
    Last edited by Bbe; 08-11-2017 at 18:17.

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