A method for controlling the power factor of a power supply line is described, the method using a power factor control cell connected to the power supply line. Advantageously according to the invention, the power factor control is performed by adjusting the turn-on and turn-off time of a bipolar transistor comprised in the power factor control cell. A cell for controlling the power factor of a power supply line is also described, of the type comprising a first and a second input terminals, a first and a second output terminals, the first input terminal being connected to the first output terminal by means of the series of an inductor and a diode, connected to each other in correspondence with an internal circuit node and the second input terminal and the second output terminal being connected to each other. Advantageously according to the invention, the control cell comprises a bipolar transistor inserted between the internal circuit node and the second input terminal and having a control terminal receiving a control signal derived from a signal having an elementary alternated trend.