Hello all,

I am no expert and have been struggling to find answers so hoping someone can help.
I have a Led strip light that is controlled by a RF PWM controller, unfortunately my power supply has coil whine that's correlated with the dimming level. I've done enough research to understand that a low pass pi filter should help, but have no idea how to calculate what inductors and capacitors I need.

Led power supply details: 12V 6A I'm drawing about 5A so well within its capacity
PWM controller details: 5-36VDC 8A 2000Hz

Any help would be appreciated, treat me as a noob.

Thanks

 

Filtering would defeat the PWM, producing a steady voltage which, in the lower half, would be likely too low to light the LEDs.

 

Filtering would defeat the PWM, producing a steady voltage which, in the lower half, would be likely too low to light the LEDs.

Not if the filter was between PSU and Dimmer. I suspect the coil whine is a beat frequency between PSU switching freq and dimmer switching freq., dropping it into audible range. I've seen (errr, heard?) this myself in the past.

 

The whine may be caused by an inductor or transformer in the dimmer.
It's not likely that an added filter will affect that.

 

In addition to possibly being from an inductor, disk capacitors have often been microphonic. due to the piezoelectric properties of the dielectric material. the way to discover which component ie producing the sound is to touch each cap and see if touching one changes the sound.
You should be able to look at the circuit schematic and see which caps would have the highest ac VOLTAGE ACROSS. THose would be prime suspects.

 

If you can ID which component is whining, a shot of hot glue often works to deaden the sound.

 

Since the PWM frequency is stated as 2000 Hz, it is not likely to be a beat note between two higher frequencies. And while hot glue would be simple, a glob of silicone sealer or adhesive will be more effective. And there may not even be an inductor in the controller, although it might be the switchmode transformer.