I think that the 3rd example is what you want to do
That was exactly what I've been looking for, thanks. Since I want to pilot more than one LED with the same PWM signal, could I clone the TIP120-resistor-LED connections in parallel on pin 9?
Ok, but you don't need 24V
Yes, I can see that. The system, though, is powered by onship transformer (tipically at 24V) or a 24V battery when standalone. The idea is to supply the system with that voltage and then use step-down converter to provide lower voltages (i.e., the Arduino supply). What do you think about that?