Drive circuit for a synchronous electric motor

Drive circuit (10) for a synchronous electric motor (1) supplied with the voltage (V) provided by an alternating current power source and including a stator (2) with at least one winding (4), and a permanent magnet rotor (5), associated with position sensor means (6) for supplying an electrical signal (R) essentially in the form of a square wave;

• the drive circuit (10) comprising:
• means of controlling the conduction of current (11-13), connected essentially in series with at least part of the stator winding (4) between the terminals (N, P) of the said power source, and comprising a first and a second controlled unidirectional conduction electronic device (12, 13), in antiparallel connection with each other, with corresponding control inputs (12a, 13a);
• and processing and control circuit means (14), connected to the said position sensor means (6) and to the said power source, and designed to control in predetermined ways the said means of controlling the conduction of current (11-13);
• the drive circuit (10) being characterized in that the said processing and control circuit means (14) comprise protective circuit means (16), designed to generate at their output a logical inhibiting signal (C), starting at every zero crossing of the motor supply voltage (V), the inhibiting signal (C) having a specified duration (t0) which is less than a quarter of the period of the said supply voltage (V);
• and enabling circuit means (17), connected to the said position sensor means (6) and designed to enable the first and second controlled conduction devices (12, 13) alternately to conduct current, in synchronization with the square-wave signal (H) supplied by the said position sensor means (6);
• the said enabling circuit means (17) being connected to the protective circuit means (16) in such a way that the conduction of current through the controlled conduction device enabled at any time (12, 13) is inhibited for the duration (t0) of the said inhibiting signal (C).