A regulator circuit for the voltage for charging a battery by an alternator comprises in succession:processing and comparison means (A4, A1, A2) receiving a fraction of an alternator voltage (D+) and generating a monotonic variation of the mean voltage regulated as a function of the load on the alternator,power switching means (CP, T101) in series with an excitation winding (Le).Semiconductor correction means (CP) are associated directly and non-resistively with the power switching means and produce an offset of said voltage fraction which varies monotonically with the intensity of the current in the excitation winding and of the load on the alternator, in order to compensate said monotonic variation generated by the processing and comparison means and to obtain a mean value of the charging voltage which is essentially constant over all of the operating range.