A synchronous rectification alternator for a motor vehicle is disclosed. The alternator includes a stator, a rotor, and a synchronous rectification system for rectifying into a DC voltage the alternating voltages supplied by the stator, and a voltage regulator for regulating the DC voltage. The alternator also includes fault detection for detecting faults in the synchronous rectification and supplying fault detection information to the voltage regulator. In one version, the fault information is supplied to the voltage regulator at fault inputs also receiving phase signals representing the alternating voltages supplied by the stator. At least one of the items of fault information is used to cause, in the voltage regulator, opening of an excitation circuit supplying current to an excitation coil of the rotor so as to produce, in the voltage regulator, a fault indication. The opening of the excitation circuit is preferably caused through a suitable command of a fast demagnetization transistor included in the excitation circuit.