... , and are then connected to an NPN transistor. The transistor used, TIP120, is actually a NPN Darlington ... standard 1N4001 diode is usually placed across each transistor as shown in the figure, providing a ... of dispersing the reverse current without damaging the transistor. Sometimes called a snubbing diode. The TIP120 ... part of the sequence turns on only one transistor at a time, one after the other. ...