Abstract: A two- or three-phase input transformer (1) feeds a conventional six-diode full-wave bridge rectifier (3) whose output terminals (4, 5) are connected through capacitors (6, 7) to the star point (2) of the second side (1b) of the transformer, and through controlled switches (9, 10) to a midpoint (8). A DC motor (11) connected between the star point and midpoint is coupled to a tachogenerator (12) which supplies a signal to the control circuit (13) operating the controlled switches, which preferably are modified MOSFETs with temperature-compensated reference voltage.