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AC rectification for LED's help

Discussion in 'LEDs and Optoelectronics' started by Elrikos, Sep 10, 2011.

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  1. Elrikos

    Elrikos

    3
    0
    Sep 10, 2011
    Hi there
    I have a quick question about running LEDs on an ac voltage. I'm trying to run 4 LEDs from 6.3v ac. Space on the boards is quite tight and I don't have space for a large bridge rectifier type arrangement. Is there another way I can get a smooth dc voltage from this setup
    Thanks
    Rich
     
  2. shrtrnd

    shrtrnd

    3,763
    485
    Jan 15, 2010
    A bridge rectifer is just four diodes. Depending on your amperage 1N4001 to maybe
    1n4007. (At 6.3VAC you probably won't need anything higher than 1N4004). They
    also make more compact bridges (like the MDA prefix bridges). The MDA950 is
    pretty small. You'd have to have an extremely small board to not have enough room
    for it. I suggest the diode and small bridge because they have longer leads than a
    PC mount bridge. You wouldn't necessaily have to mount it on the board itself, you
    could find a place to tie the longer leads into your circuit.
    Just some ideas for you to consider.
     
  3. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    What LED's are those, and what's the application? Does the power need to be absolutely battery smooth? There are SMD bridges you know.
    But if they're close together illuminating the same spot you can usually dispense with rectification and simply connect the LED's in antiparalell.
     
  4. Elrikos

    Elrikos

    3
    0
    Sep 10, 2011
    hi there,
    thanks for the help so far. The project is a part of a twilight zone pinball table.
    The table itself has a mechanical clock which times down various modes in the game. Boards inside have optos which the minute and hour hands break as they spin, so the game software knows what time the clock is showing. It also has 4 small lamps inside to illuminate the clock face. The problem is that the lamps burn quite hot and over time damage the board and opto's. This is why i'm looking to put LED's inside instead as they will burn cooler.

    the lamps run on the pinball table general illumination circuit which is 6.3v ac. The only reason i was looking to rectify to DC is i'm told that running the LED's on AC will cause them to flicker and be distracting. Any solution which avoids that is fine by me!

    Thanks again
    rich
     
  5. jackorocko

    jackorocko

    1,284
    1
    Apr 4, 2010
    Would it be possible to add in a cap and another diode in series to help keep the LED from turning on and off completely?
     
  6. Elrikos

    Elrikos

    3
    0
    Sep 10, 2011
    It would depend on the physical size of the cap. What kind of value would be needed?
     
  7. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    There are LED bulb replacements available that runs on AC.
    Or, if you want to make them yourself you can put two LED's in one bulb socket with one resistor. Illuminating the same area they won't flicker much more than a bulb.
    How flicker resistant the opto arrangement is I can't say though.
    Is there no room to put a rectifier & cap somewhere in the 6.3V wiring that leads to the clock?
     

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  8. Externet

    Externet

    744
    162
    Aug 24, 2009
    You do not need a bridge rectifier. Connect 2 series leds in counterparallel to another 2 series leds; fed current limited by a small resistor. Perhaps ~100 Ohms?

    AC-------------Y------------|>|--------|>|---------------X-------\/\/\/\/\/\-------------AC
    0000000000Y------------|<|--------|<|---------------X

    Join 'X' together
    Join 'Y' together.
    Ignore the '00000'
     
    Last edited: Sep 11, 2011
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