An active rectifier of a rotary electric machine, in particular an active rectifier for alternators, for example for rectifying alternating currents (AC) to direct currents (DC) for charging batteries on vehicles, is disclosed. The active rectifier may include a plurality of power MOSFET transistors and a detecting and driving circuitry all mounted on a single substrate to form a half-bridge module. A number of at least two and up to N modules may be connected together to serve as a two and up to N-phase rectifier. Each module is connected in a way to rectify currents from one phase of the electric machine and has an individual power supply for the detecting and driving circuitry. The power supply may receive the power from the phase which is being rectified and operates independently of the alternator's voltage regulator.