The description concerns a voltage regulator (12) for regulating the output voltage (UB+) of an alternator (10) which is driven by an internal combustion engine. The voltage regulator (12) has an additional circuit (24) which evaluates the exciter current duty cycle (T) and supplies a signal (S1) at its output which is high when the exciter current duty cycle is high and low when the exciter current duty cycle is low. The circuit (24) is integrated in the voltage regulator (12) and the output signal (S1) supplied by it is transmitted via an additional regulator terminal (DA) and can be fed to the control device (25) of the internal combustion engine, where it is used, for instance, to increase the idling speed of the engine and accordingly also to increase the alternator speed and thus the power delivered by the alternator (10). It is also possible to switch off unnecessary consumers with this signal.