National LED driver LM3404 etc

Discussion in 'General Electronics Chat' started by rbg5k, Jan 27, 2010.

  1. rbg5k

    Thread Starter New Member

    Jan 26, 2010
    On most of these chips there is a DIM control which accepts a PWM signal to act as a dimmer. LM3404 is the one I have.

    I was wondering if anyone is familiar with these chips and whether I could make the driver flash on / off with this pin?

    It sounds like I can with logic hi/low.

    Wanted to save time by asking before I breadboard it.

  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    From a quick glance at the data sheet this would not seem like a problem. The only restriction they put on the frequency of the DIM signal is

    In other words, as long as you are not switching the DIM pin HIGH and LOW faster than the chip and LEDs can take, you should be fine.

    It appears from the Block Diagram that the DIM input just goes into a comparator.
  3. SgtWookie


    Jul 17, 2007
    I haven't used that particular IC, but the DIM input is for PWM; it enables/disables the regulators' internal MOSFET. That should do just what you want.
  4. rbg5k

    Thread Starter New Member

    Jan 26, 2010
    Thought so -- always nice to get confirming opinions though.

    This is a great forum.

    A recent discovery -- don't know how I missed it.