Patent ID: 7880427

Claim:
A method of operating an electronically commutated motor having two winding strands ( 52 , 54 ), a permanent-magnet rotor ( 36 ); terminals ( 28 , 30 ) for connecting the motor to a current source ( 22 ); a stator ( 102 ) having a winding arrangement, which arrangement comprises a first winding strand ( 52 ) that has a first controllable semiconductor switch ( 70 ) associated with it in order to control current in the first winding strand ( 52 ), and a second winding strand ( 54 ) that has a second controllable semiconductor switch ( 80 ) associated with it in order to control current in the second winding strand ( 54 ), the first semiconductor switch ( 70 ) and the second semiconductor switch ( 80 ) together defining a subset of semiconductor switches and serving for electronic commutation; a field-effect transistor ( 50 ) arranged in a supply lead from a terminal ( 28 ) to the winding strands ( 52 , 54 ); an apparatus ( 74 ) for preventing a return current, which apparatus is arranged in a common supply lead ( 72 ) to the semiconductor switches of the subset; said method comprising the steps of: as a function of a desired operating state of the motor ( 20 ), applying a PWM signal ( 24 ) to a control input (G) of the field-effect transistor ( 50 ) to alternately switch it on and off without thereby turning off a currently conductive one of said subset ( 70 , 80 ) of semiconductor switches, so that in operation, subsequent to a blockage of the field-effect transistor ( 50 ), a decaying loop current (i 2 , i 3 ) flows through the semiconductor switch of the subset that is conductive at that instant, and through the other semiconductor switch of the subset or a recovery diode ( 76 , 81 ) associated with the latter, and through the first and the second winding strand ( 52 , 54 ), which loop current generates a torque in the motor ( 20 ).