PWM Assistance Needed

Discussion in 'The Projects Forum' started by Rowan, Apr 13, 2008.

  1. Rowan

    Thread Starter Member

    Jun 1, 2005
    12
    0
    3 years later and I am back to dig up this thread from the past... hgmjr you did a great job helping me out last time with this problem, I was wondering if you are able to assist again? This thread was the first thing I thought about when thinking about this problem :)
    I need a PWM circuit to drive an LED on an LCD Backlight. Is it possible to have a circuit made up with with outputs from a 3.3v DAC to drive the 5V LED between 10-80% PWM?

    This would be greatly appreciated,
    Thanks hgmjr!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Welcome back Rowan, its been a while since your last log-in.

    I have taken the liberty to move your question out of the dormant thread and into its own dedicated thread.

    You may want to do some additional searching in the forum with keywords PWM or pulse width modulation. PWM is a popular topic in the forum and there have been a number of good circuits posted.

    hgmjr
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Here is a thread for example on PWM and LED dimming. In the thread there is a link to an off the shelf module in case you are interested in purchasing a solution.

    hgmjr
     
  4. Rowan

    Thread Starter Member

    Jun 1, 2005
    12
    0
    Thanks for the quick reply :)
    I probably should've done some searching first, however I came to this thread to see if the attachments were still here and decided to leave a reply.

    Thanks for the link, i'll check it out. Does the off the shelf module have a schematic? I need to put this circuit on a pcb with the LCD controller.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I put up an easy-to-build PWM circuit in the Projects Collection several months ago.
    http://forum.allaboutcircuits.com/showthread.php?t=9016
    If you want to power the circuit from less than 10v, you can use a Darlington transistor instead of the power MOSFET. A ULN2003/4 or ULN2803/4 is an easy-to-use and inexpensive IC that contains seven or eight Darlington pairs, each output has 500mA sink capability, and each input has resistors to limit base current. If 5v or less operation, use the 2x03, for higher use 2x04. The difference is the resistance in the base current limiter resistors.
     
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