De-Flickering Cheap LED Christmas Lights

Discussion in 'The Projects Forum' started by njbair, Nov 27, 2012.

  1. njbair

    Thread Starter New Member

    Sep 1, 2011
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    Hi, folks.

    I bought a pre-lit LED tree on clearance last year right after Christmas. The tree looks great except for the fact that the LEDs flicker. It's my understanding that this is caused by the unrectified AC voltage so that the LEDs are running at a 50% duty cycle at 60Hz.

    My question is, can I just build a bridge rectifier to provide DC current to the lights? It sounds simple enough but I know there are big differences between AC and DC and I'm not sure how this change would affect the LEDs. I don't have specifics on the LEDs other than that they appear to be the same, standard mini bulbs that all Christmas light strands use, including the flicker-free ones. If more info is necessary I do have a scope and most other common test equipment.
     
  2. JohnInTX

    Moderator

    Jun 26, 2012
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    The LEDs are probably wired several in series to make up a string that uses close to line voltage. This series string is then wired with another like it in inverse parallel so that they each use 1/2 of the AC cycle. Wired like this, using a bridge to supply rectified DC to the line plug would result in half of the LEDs being off and the other half running at twice the power.
     
  3. njbair

    Thread Starter New Member

    Sep 1, 2011
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    0
    Makes sense. If I were dealing with a loose strand instead of a pre-lit tree, I might undertake to rewire it for DC. Oh well, it was worth a shot.

    Kind of a shame that just a few dollars worth of passive components got in the way of this being a perfect tree.

    Thanks!
     
  4. wayneh

    Expert

    Sep 9, 2010
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    You might be able to make a custom power supply with doubled or quadrupled frequency. It would still be AC but you wouldn't be able to see the flicker anymore. This could actually be a popular item, as I know a lot of folks dislike the LED lights due to flicker.
     
    JohnInTX likes this.
  5. JohnInTX

    Moderator

    Jun 26, 2012
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    What a great idea.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    Hah, well the devil is in the details. I know there are a lot of frequency doubler circuits out there but I'm not sure how you'd adopt that to this application. At least the current and power are not too extreme.
     
  7. njbair

    Thread Starter New Member

    Sep 1, 2011
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    You could pronably never sell something like this off the shelf, because I think that anything with a standard 2-prong receptacle has to conform to a standard voltage & frequency output. But it is a good idea.
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    The rear LED lights on cars, trucks and buses are anoying because they flicker.
    I wish they would use a much higher PWM frequency for dimming them.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    I gather that airplanes use 400Hz power systems. That'd be great.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    I've never seen a line connector rated for it's frequency. Current yes, voltage yes, never seen frequency rated.
     
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