LED Dimming and flicker

Discussion in 'General Electronics Chat' started by proaudio4, Apr 22, 2007.

  1. proaudio4

    Thread Starter New Member

    Apr 22, 2007
    3
    0
    Here' s my issue:
    I purchased cheap DMX LED PAR lights.
    They are set up with over 100 LEDs with over 30 LEDs on each leg of the RBG circuit.

    When dimming these lights, I have a lot of flicker when shooting video.
    I want to modify the circuit to minimize flicker.

    If I had bought the more expensive units. they brag about no flicker for video pro shoots.

    I realize these are using PWM for dimming. If I dropped a cap across each circuit R, G, and B, would this approach work correctly if I calculated the correct time constant?

    If this is not the right direction, please help me find a way of making these work.
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    The better units use a higher frequency PWM. Adding a cap would only diminish the range of operation, not eliminate flickering.
     
  3. proaudio4

    Thread Starter New Member

    Apr 22, 2007
    3
    0
    Thanks...
    Hmm... I thought that by having the ON/OFF state ramp a bit, may make flicker less apparent?

    So. am I out of luck on this?
    I realize a schematic would be helpful.
    They're made in china (of course), I'm not sure if it's possible to get a shematic on these.
     
  4. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    I suspect the LED driver is having issues with how you are dimming them. What are you dimming them with? Also it would probably be easier to filter those rather than dim them.
     
  5. proaudio4

    Thread Starter New Member

    Apr 22, 2007
    3
    0
    All dimming (and the only dimming) is done via DMX control.
    Like I mentioned before, the higher end units, such as the Elation Design LED 36 offer flicker free for video.

    Here's a section direct from its manual of features:
    • Low power consumption
    • Minimal heat emission
    • Maintenance free operation
    • Equipped with 36 one-watt LEDs: (12 red, 12 blue, 12 green)
    • High power LEDs manufactured by Lumileds, USA
    • 50,000 hours plus, LED life
    • Step less RGB color changing
    • Strobe-effect with a maximum flash rate of 18fps
    • DMX-controlled operation or stand-alone operation with Master/Slave-function
    • 8 built-in programs can be called up via DMX-controller
    ~ 48 preprogrammed scenes per a program
    • Sound-controlled via built-in microphone
    • 6 DMX-channel or 3 DMX-channel operation
    • DMX-control via standard DMX-controller
    • Flicker-free operation for television and film
    • Compact design: fits in 12” box truss
    • Brilliant light output

    Manual:
    http://www.elationlighting.com/pdffiles/DLED36manual_rev1206.pdf

    This is a known issue with cheap DMX LED lights. I knew about it before I bought them. I was hoping to find a way of fixing them. I'm not sure how them are using the PWM. I was hoping to see an easy LM555 circuit where I could try some different caps for the timing. No LM555 that I can see.
     
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