The invention relates to a control loop (10) which is installed in a voltage regulator of a motor vehicle alternator and controls an output voltage of the latter by adjusting an excitation current of the alternator. The control loop includes, at the input, means for measuring (31) the output voltage by sampling, generating a measurement signal (Um), error-calculation means (13) generating an error signal (e) equal to a difference between the measurement signal (Um) and a set value (Uo), means for processing the error signal (e) including an amplifier (14) and generating a control signal (Ysat) and, at the output, means (35) for generating a control signal (PWM) controlling excitation control means in accordance with the control signal (Ysat). According to the invention, the processing means also include a phase-advance filter (24).