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Led dimming help.

Discussion in 'LEDs and Optoelectronics' started by AGLite, Mar 31, 2012.

  1. AGLite

    AGLite

    35
    0
    Feb 19, 2012
    Hi guys,

    I have a lighting controller that I recently put two pre-built LED bars in. The bars have 16 blue LEDs in each and run off of 12 volts. when I put a pot. in the power in it dims very bad and 4 of the LEDs are all that dim the rest turn off. I don't really care about dimming. I just want them to turn on smoother, so what I want is when i turn on the toggle they slowly fade to full brightness. I appreciate all the help i can get.

    Thanks,

    Austin.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    You would need to get a PWM controller to do this.

    Here is a commercial unit (no doubt you can get them more locally).

    And here is a description of how they work so you could make your own if you wanted to.
     
  3. AGLite

    AGLite

    35
    0
    Feb 19, 2012
    so if i say hook the dimmer up and set it to full brightness. and then turn on the toggle, they will slowly fade up?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    No, you wind the brightness up on the controller and the brightness goes up.
     
  5. AGLite

    AGLite

    35
    0
    Feb 19, 2012
    do u know how to make it do that
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    Have a look at a constant current source using an op-amp to compare the voltage across a current sense resistor with a reference voltage.

    Then get your reference voltage from a voltage divider.

    Place a capacitor across your voltage reference and the constant current source will slowly (depending on the size of the resistor and the capacitor) ramp up to a maximum brightness.

    It may require some tweaking and it may be best if your load does not require a current source (otherwise your reference voltage will need to be regulated then divided)
     
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