Questions on LED dimming with a PWM Driver wired to a Potentiometer

Discussion in 'Power Electronics' started by HPY, Aug 20, 2018.

  1. HPY

    Thread Starter New Member

    Aug 20, 2018
    Hello everyone!

    I hate having to ask stupid questions, I'm not an expert in this at all and after quite a bit of research I'm now stuck on a few basic issues.

    I'm trying to design and put together a dimming by PWM table lamp with a rotary potentiometer type switch that would dim the light and switch it off. I looked into getting a BuckPuck LED Driver with a 5K potentiometer -

    However I'm now looking at getting a Mean Well LDD-L (WIired version) Step Down Driver which seems to do the same thing, it's slightly cheaper, smaller and I can get it at my local tech store (pdf attached with driver spec).

    My LED spec is 7W / fV 11.0~14.0V / 550mA

    So my questions are:

    - What power supply do I need for the driver to work with this LED? I'll be using the 500mA driver and I assume the power supply output needs to match the LED input. So would a AC-DC 12v 0.5A power supply work?

    - How would I wire up a potentiometer to the driver for the PWM dimming to work? What kind of resistance would the potentiometer need to have? Could the Potentiometer also be used as an on/off function?

    Again, sorry for the basic questions or if they've been asked before. I'm new to this.

    Thanks in advance for any help!
  2. dl324

    AAC Fanatic!

    Mar 30, 2015
    Welcome to AAC!

    A cursory glance of the datasheet gives a drop out voltage of 4V for the current source. To power an LED that could require as much as 14V, you'd need to provide at least 18V.

    For dimming, you need to provide a voltage of 0-8V. You could use a zener diode to provide the 8V and put the pot across the zener, connecting the wiper to pin 3. The datasheet says the input current is 1mA max, so the current in the pot should be at least 10mA.

    If the input voltage to the current source is well regulated, you could use a voltage divider and eliminate the zener diode.
    Last edited: Aug 20, 2018
    HPY and -live wire- like this.