PWM question

[blueflyer]

I bought an LED light strip from an auto parts store that had a dimmer (I assume a PWM) attached to it. I cut off the dimmer and attached the dimmer to another LED light strip. I applied power/ground to the dimmer and the LED strip wouldn't come on. why did that not work?

[lrgabriel]

It could be many things, but the first thing I'd do is grab a meter and see what the dimmer puts out (and that you have your polarities correct).

Different manufacturers do different things with respect to forward voltage--it's possible your old strip steps down voltage in the dimmer and the new one does it directly on the LEDs.

[blueflyer]

I was afraid of that. ok thanks.

[jdeas]

LED drives also come in several flavors.

Some use in-line resistors with parallel LED's and modulate (PWM) only the voltage. (legacy incandescent modules)

Some use no in-line resistors and modulate the voltage through a current source.

The most efficient ones series the LEDs to reduce wasted heat load and use the current source method.