Note: Schematic is not my best work, but this should pass on information.
I've designed the following circuit; The purpose of this is to have the Arduino Nano control the WS2811 LEDs and also control their power via MOSFET IRF540N.
Problem is: When I ground the MOSFET Gate pin to 0V, the LED's still glow, meaning that there is still a flow going on. I've grounded manually via wire.
Only when I remove the connection from MCU pin D4 and WS2811 pin DI will the LED's go out like intended. So my conclusion is that the MCU pin D4 is Weakley conducting to ground(?).
The only advice that I've gotten is to use a P-Channel MOSFET instead of N-channel. I don't know what options I have at the moment. Would adding a diode in between the MCU and LED help here?