A control and power module for a rotating electrical machine comprising a power circuit containing a number of branches, and a control circuit designed for controlling the power circuit when the machine operates in a nominal mode. The inventive module is characterized in that the control circuit is also designed for monitoring an output voltage from the power circuit and blocking at least one branch of the power circuit in a conduction state when the output voltage reaches an at least first threshold value so that the machine functions in a degraded mode. The invention is for use in an alternator starter.