I am controlling a 6x6 matrix of LEDs using a PLC with sourcing outputs and sinking outputs (24V). However, there is an issue with current leaking through to other lights.
For example, in the schematic below if I turn ON L25 (Source) and L30 (Sink), LED 16 will illuminate, but LEDS 4,10,22,and 28 will also slightly illuminate. Additionally, LEDs 13-18 will slightly illuminate. It appears that current could be using the open sinking as a ground or that the LEDs are not acting as perfect diodes.
The leakage LEDs are very dim and initially, I could not observe the problem. However, since running the matrix over several months, the leakage lights have become brighter. I checked using a multimeter and found that 1-3V are leaking across to other LEDs.
My question: what is a possible issue here? How can I resolve this most easily as I do not want to make significant changes to the matrix.
Thanks in advance.