Patent ID: 7479755

Claim:
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 ( 12 a , 13 a ); 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 (t 0 ) 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 (t 0 ) of the said inhibiting signal (C).