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High power LEDs for strobes

Discussion in 'Electronics & Electrics' started by Dark Orange, Aug 27, 2017.

  1. Dark Orange

    Dark Orange Member

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    I am wanting to build an LED strobe for photography work - the requirements are that the pulse duration be about 2-5ms, and have serious light output.

    Back a few years ago when I was looking into it, a crapload of individual bright white LEDs could do the job, but even overdriving them 10-20x the build just became impractical size wise.

    Fast-forward to the modern times where high-wattage COB modules exist. I have done some looking around but can't find much info on the behavior of the drivers for these. While I assume the AC powered chips are unsuitable for my needs, I have found some 100W units that are still 10vDC. Could these be driven with PWM and overdriven?
     
  2. Menthu_Rae

    Menthu_Rae Member

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    Could you find a reference driver circuit suitable for a nice COB LED like the Bridgelux Vero series and add an external shunt FET?

    See here:

    http://www.ti.com/lit/an/snva605/snva605.pdf

    The scope plot I think shows the LED turning on and off within 36.12uS... So you could probably use something like the LM3406/HV with ~48VDC input and a Bridgelux BXRC-50C4001-C-74-SE.

    https://www.digikey.com/product-detail/en/bridgelux/BXRC-50C4001-C-74-SE/976-1566-ND/6557069

    If you drive that at nominal you'll get ~7000lm - if you overdrive it close to 2A that goes up above ~10,000lm.

    Curious what actual electronics gurus think...? :confused:
     
  3. RobRoySyd

    RobRoySyd Member

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    I don't know if this will be a problem or not.
    White LEDs produce light output long after the current has stopped. White LEDs are similar to fluorescent lamps, both use an excited phosphor and it'll continue to output light after the excitation has stopped.

    Mightn't be a problem for still photography but it sure excludes them from being used as a strobe light. The problem could be avoided by generating white light using RGB LEDs.
     
  4. merlin13

    merlin13 Member

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    Apart from the continuing light output on COB arrays that'd cock up a "proper" strobe application that 'Rob mentions, there's another couple of points to note:

    - Snaploading of the power source at such high currents and low volts means if you go for multiple COB arrays (which I'm reading that you might be looking at...) means that apart from thundering huge capacitor banks and/or a thunderingly beefy power source your main wiring could end up looking like jumper cables in size.

    - Pretty sure that overdriving those COB arrays would burn them out far quicker than normal nominal volts/amps operation, even at the short pulse duration you're looking at.
     
  5. OP
    OP
    Dark Orange

    Dark Orange Member

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    Thanks for the info folks, lots of extra info to consider. Just bit the bullet and ordered 4x 24v/100W units for under $30 which was cheap enough to just experiment with.

    Worst case, I end up with a decent light source for macro photography :)

    ps. I am an industrial sparkie, big electricity is my bread and butter.
     

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