Brighter, faster, flashes from an LED-based flash gun – part 1

This is a quick post to show that it is relatively easy to get very fast, bright, flashes from larger LEDs than those I reported upon in an earlier post. I used the same circuitry as before but this time used it to drive a 10W 9-element COB LED at ~50A. This resulted in flashes bright enough to take pictures. The picture below  of my Dremel running at maximum RPM was taken with my iPhone (!). Dremel claim the drill I have will run at 32,000RPM. The flash duration was 5us and the LED was used in “stroboscopic mode” in the dark. I was quite impressed with the picture given that the edge of the disc is moving at about 83 metres per second (~300kph).

Dremel cutting disc running at 32,000 rpm.

Dremel cutting disc running at 32,000 rpm.

Here is a movie of the LED running in strobe mode:

Next steps are to increase the speed of the flash to 1us or better, write code so that the Arduino controller can respond to signals from my Camera Axe trigger, and upgrade the circuit used to drive the LED to use higher currents (100A). The heat-sink I used is there so that the LED can also be run in continuous mode with normal currents. The chip I used is incredibly bright…..warning to anyone who uses these…don’t look at them directly!

Note added 14/02/15: The 10-90% rise-time for the 10W LED is about 2us, four times longer than that for the single 3W star LED. As the traces below show, the 10W LED is able to produce light pulses of 1us duration but, though not obvious from the image, this is at the expense of  about 40% of its light output per unit time. The rise and the fall times are such that the light pulse far outlasts the 500ns voltage pulse used to create it. This may be due to the greater intrinsic series resistance and capacitance of the larger chip. It doesn’t bode well for driving bigger COB LEDs for very short durations. Fortunately, it looks like the 10W chips will go fast enough and bright enough for some of the applications I have in mind most of which require pulses in the 5 – 500us range.

To get the Arduino to produce sub 5us pulses, I used the PORT commands to toggle the digital pins and I used and the ‘no operation’ assembler command, nop, to give me the duration I wanted. Each ‘nop’ takes about 60ns.

Light output in yellow, command pulse in blue.

Light output in yellow, command pulse in blue.



About petermobbs

Inveterate meddler.
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3 Responses to Brighter, faster, flashes from an LED-based flash gun – part 1

  1. Thomas says:

    Hi Peter, your work is really cool.
    I’m trying to make some High speed strobe (to make a kind of zootrope) with 10w or 100w leds by overdriving them, but i’m a novice in this field. Do you have any schematics of your project or some recommendations/ressources ( i really would like to try your design) ?

  2. Ian McCulloch says:

    Hi Peter — I agree with Thomas .. this work you did is really cool. From your experimentation do you have an idea at what pulse duration the LEDs fail when being driven say 10x the rated current? Can they last say a few milliseconds or are we really limited to the microsecond range for such large current surges?


    • petermobbs says:

      Hi Ian – it is very difficult to be hard and fast here. It depends very much on the construction of the LED. I have simply taken the LED concerned and pushed it until it blows and then stepped back from that current and duration to test it in the longer term. At a guess, I think you could try flashes in the low (1-3) milliseconds. All the best, P.

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