12V DC DMX LED Controller needs to be reduced to 5V
If you can "inject" 5 V from a separate source, you can build your own low-side PWM like this:

EDIT: New schematic due to lowside PWM from your driver. This is kind of dirty. If you want to improve the efficiency and probably dimming at very low duty-cycles, you should consider an inverting gate driver instead of R1 and M1.







simulate this circuit &ndash; Schematic created using CircuitLab