IR Illuminator - to pulse or not to pulse?

Discussion in 'General Electronics Chat' started by gmglickman, Aug 5, 2008.

  1. gmglickman

    Thread Starter New Member

    Aug 5, 2008
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    Is there any advantage to pulsing IR LEDs at higher current vs. continuous? Will they appear "brighter" to the camera? For example, my LEDs (Vishay TSHG6410) list maximum ratings of:
    Forward current =100 mA max
    Peak forward current (tp/T = 0.5, tp = 100 µs) =200 mA (50% duty)
    Surge forward current (tp = 100 µs) = 1 A (single pulse??)

    and radiant intensity is:
    IF = 100 mA tp = 20 ms Ie 90 mW/sr
    IF = 1 A tp = 100 µs Ie 900 mW/sr

    If I pulse 200mA at 50% duty, would this be any brighter than a continuous 100mA?

    How about 1A at a 1% duty cycle (100µs on, 10Hz) or does this exceed the maximum?
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,699
    907
    The main purpose for pulsing is avoidance of noise. The receiver only responds to a particular carrier pulse rate, such as 38 KHz.

    Of course, one can drive them harder for better range with pulses too.

    John
     
  3. gmglickman

    Thread Starter New Member

    Aug 5, 2008
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    This is for IR illumination of a digital infrared image. It's not modulated IR for communication or remote control.
     
  4. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    It is not a good idea to drive the leds (or every electronic component) to their limits because this degrades their life. Also, if you pulse them it does not mean they will look brighter because their brightness depends on the pulsing frequency. If you pulse them with a too low frequency they wont look bright because of the effect of persistence of vision (search for it in google if you like). On the other hand, if you pulse them at very high frequencies they wont have enough time to turn on and they wont be bright. So, you have to find the proper frequency to pulsate your leds depended on their turn on time. About 1KHz will be good.
     
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