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Dimming LEDs

Discussion in 'Electronic Basics' started by Simon Griffiths, Jul 21, 2005.

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  1. Dear All,
    I am currently building an art project but cannot seem to
    get my LED's to dim properly. I have tried capacitors but to no avail. I've
    heard that diodes could dim the LED's but I would like the lights to dim
    slowly on and off. Thanks for any tips.

    Simon Griffiths.
     
  2. One way is to PWM the LEDs, with the modulation rate being at or above
    60-80Hz.

    Jon
     
  3. Byron A Jeff

    Byron A Jeff Guest

    Dimming LEDs by changing voltage or current is a black art.
    Black art.
    Um. LEDs are diodes.
    Now you need an active component in addition: a triangle wave generator.
    You can find a circuit by clicking I'm feeling lucky on Google with
    the phrase triangle-wave generator circuit.

    The third link under 'LED dimmer' which goes to Mike's flight deck has
    both the theory and the circuit of LED dimming.

    Good luck.

    BAJ
     
  4. ehsjr

    ehsjr Guest

    Go here: http://ourworld.compuserve.com/homepages/Bill_Bowden/
    Look for "fading red eyes" .

    Ed
     
  5. Guest

    LED dimming by current control (analog) is hardly a black art. For
    simple dimming, a voltage controlled current source with sufficient
    compliance would work fine.

    http://www.national.com/ds/LM/LM101A.pdf#page=11

    The top of page 12 of this shows a bilateral current source which would
    work if you limited your control voltage to the correct polarity.

    5 years ago I did a prototype linear LED controller using a now
    discontinued Burr-Brown SHC615 driving the LED and sourced with 15KHz
    to 30MHz analog video to test photosensor/preamp assemblies. It worked
    very well.

    You can do this with one opamp.

    GG
     
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