questions for simple PWM circuit

Discussion in 'The Projects Forum' started by, Jul 4, 2012.


    Thread Starter New Member

    Jun 27, 2012
    I know this is an old topic. I would like to use this circuit as an LED array dimmer but I have a few questions.

    12V input
    LEDs- 3.6V, 30mA (typical) - 3 parallel branches with 3 series LEDs

    R1 = 500k 500mW 20%
    R2 = 6k 3W 5% (?)
    Rload = (is this where the LEDs are inserted ?)
    C1 = 3.9nF 50V 10%
    Rlimit = 40 3W 5%
    (a current limiting resistor for the LED branches. Can all three branches share a resistor or is it best to have 3 separate resistors?)
    Q1 = part number IRFI540NPB (correct one?)
    D1 & D2 = 1N914

    What are points A and B in the schematics provided by SGT Wookie?

    If I double the number of LEDs 6 parallel branches will any component values change.

  2. Markd77

    Senior Member

    Sep 7, 2009
    All resistors can be 0.4W or whatever you have handy.
    You need a resistor for each LED.
    The diodes are fine.
    Pretty much any N-channel MOSFET is OK.
    A and B are the traces on the oscilloscope.
    The same components should be fine for 6 LEDs.
    Rload is where the LEDs and limit resistors go.