LED driving

Discussion in 'General Electronics Chat' started by bedfordwheelnuts, Apr 27, 2011.

  1. bedfordwheelnuts

    Thread Starter New Member

    Apr 19, 2011
    Hi all,
    I am looking at driving six to eight LEDs in series.
    I have one power supply at 30VDC Pulse Width Modulated.
    I want to create a constant current supply of up to 100mA to drive the LEDs.
    I have looked at a number of IC's that can drive the LED's and also use a PWM for dimming, but these use a constant DC supply to drive them.

    I expect the +28V to be used for the dimming.

    Any ideas?
  2. Wendy


    Mar 24, 2008
    Uhh, why did you list this as Ebook help?

    Look at chapter 5 of this...

    LEDs, 555s, Flashers, and Light Chasers

    It will get you where you want to go.

    For dimming LEDs, PWM is definitely the way to go, as the article explains. It does not replace the required resistor, but it does supplement it.

    Chapter 2 covers simple constant current sources, and simpler versions can use a simple transistor for good effect.


    For this design the emitter resistor sets the current, and the formula is 0.7V/Re.

    Another variation on the same theme...

    Last edited: Apr 27, 2011