The invention relates to a voltage regulator (43) for a motor vehicle alternator (44). The device comprises a control module (I) for controlling an excitation current (lexc) in an excitation winding (3) of the alternator (44) according to a difference (5) between a setpoint voltage (DO) and a control voltage (Dbat) of an on-board network (9). The on-board network (9) of the vehicle is powered by a battery (10) to which the alternator (44) is connected. According to the invention, the voltage regulator (43) further comprises a safety module (30) that monitors the control voltage (Ubat) and which is separate from the control module (I). In a particular embodiment, the control module (I) and the safety module (30) are connected electrically by external bonding interconnections.