I wanted to add custom RGB lighting behind my monitor, and control it with a microcontroller.
Circumnavigating the monitor required 44 LEDs from a WS2812B strip. The power requirements were ~2.65A @ 5V (3 channels * 20mA/channel * 44 LEDs), so this couldn’t be powered this from USB alone.
I bought a Molex 4-pin to 5V adapter to source 5V from my PSU. The final wiring diagram looked like this:
PSU 5V and Motherboard USB to WS2812B LED Strip
The setup worked, but when I turned off my PC I noticed the fans kept spinning slowly and some RGB devices attached to my NZXT Smart Device V2 remained illuminated.
I suspect there may be some backfeeding from either the PSU 5V through to the USB cable or visa versa. Can someone please help me understand what might be going on here? Diagram of
LEDs behind the monitor powered by PSU, controlled over USB, and an initial testing pic.
By the way, I’m using a Seeeduino XIAO microcontroller to drive the WS2812b LED strip. I’m aware that the XIAO runs on 3.3V TTL, while the WS2812b strip runs on 5V TTL. But I found through experimentation the XIAO was able to drive the WS2812b LED strip without any issues.
