A regulator has a circuit generating an activation command by bringing, to a first voltage higher than a high reference voltage, a bidirectional line connected to a detection circuit for detecting a status of the activation command. The detection circuit comprises generation means for generating a fault signal from a flag indicating a failure of the alternator, linking the line to a ground by means of a switching element, thus bringing the line to a second voltage lower than a fault voltage lower than the high reference voltage, and the control circuit comprises detection means for detecting the fault signal. The control circuit further transmits a setpoint PWM signal having a maximum higher than the high reference voltage and a minimum lower than a low reference voltage higher than the fault voltage, a duty ratio of the setpoint signal being representative of a setpoint voltage (V0) of the regulator.