LED dimming

Discussion in 'General Electronics Chat' started by c.marsh, Apr 2, 2013.

  1. c.marsh

    Thread Starter Active Member

    May 16, 2009
    100
    0
    hi all, I dont post very often but require a little assistance.

    I'm working on a lighting project which uses 2x 3mm white leds and 2x white SMD's running off a 12v power supply.

    I was wondering if i could use a 470ohm potentiometer on each led/smd to allow for adjustable brightness?

    The point being to adjust each led/smd to a desired light level while keeping the circuit board to an absolute minimum due to space limitations.

    thanks
     
  2. Tealc

    Member

    Jun 30, 2011
    140
    10
    Do you want them adjustable independently of each other? If not then a 555 PWM circuit will be a solution that won't take up that mcuh space.

    You could use a potentiometer and a resistor in series with your LED but you'd have to be careful as pots have generally low current ratings. To overcome this you could use a transistor controlled by a potentiometer.

    LEDs don't dim linearly though so you may find you really have to twiddle a lot to get them to dial down, PWM control is much better.
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,226
    If you use a pot, you also need a fixed resistor in series so the current doesn't exceed the LED's rating.
     
  4. c.marsh

    Thread Starter Active Member

    May 16, 2009
    100
    0
    independently adjustable.

    so power > pot > resistor > led

    or

    power > resistor > pot> led?

    im thinking the second option but might be wrong.
     
  5. Tealc

    Member

    Jun 30, 2011
    140
    10
    Makes no difference as the same current will flow through the circuit whichever way they are organised.
     
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