Patent ID: 8058825

Claim:
An electronically commutated motor (ECM) comprising: a permanent-magnet rotor ( 22 ); a stator having a plurality of winding phases ( 24 , 26 ); a respective semiconductor switch ( 40 , 42 ) controlling current flow to each stator winding phase ( 24 , 26 ); a microcontroller ( 30 ) commutating said motor by controlling ( 5 , 6 ) operation of said semiconductor switches ( 40 , 42 ); and a differentiating circuit ( 90 , 100 ) for differentiating a voltage signal occurring in at least one of said winding phases, and for furnishing ( 12 , 13 ) values measured by said differentiating to said microcontroller ( 30 ) for detection of a direction of rotation of said rotor, wherein respective voltage signals from at least two phases are differentiated, and instants for sampling of voltage values are selected with predetermined temporal spacing with respect to crossing points ( 182 , 184 ) at which said differentiated signals have substantially identical values.