Patent ID: 6969963

Claim:
A motor driver including a plurality of output circuits each having an upper arm side switching element and a lower arm side switching element connected in series, a current being supplied to a motor from a connected point between the upper arm side switching element and the lower arm side switching element of each of the output circuits, the motor driver comprising: a current detection resistance connected in series with the plurality of output circuits in common for detecting a current supplied to the plurality of output circuits; a position detection section for outputting a position signal corresponding to the position of a rotor of the motor; a phase switch circuit for selecting one switching element of one output circuit among the plurality of output circuits according to the position signal and putting the selected switching element in the ON state during a time period corresponding to a predetermined electrical angle, the phase switch circuit also performing switching operation for lower arm side switching elements of plural output circuits among the remainder of the plurality of output circuits when the selected switching element is an upper arm side switching element, or performing switching operation for upper arm side switching elements of plural output circuits among the remainder of the plurality of output circuits when the selected switching element is a lower arm side switching element; and a conduction period control section for generating a switching operation control signal for controlling the switching operation by the phase switch circuit according to an input torque instruction signal and a voltage generated at the current detection resistance so that each of a plurality of time periods obtained by dividing the time period corresponding to the predetermined electrical angle has a first time period in which a plurality of switching elements among the switching elements subjected to the switching operation are put in the ON state and a second time period in which one of the plurality of switching elements put in the ON state during the first time period is kept in the ON state, and outputting the switching operation control signal, wherein the conduction period control section generates the switching operation control signal so that when the number of times of switching operation performed during the time period corresponding to the predetermined electrical angle is equal to or less than a predetermined value, a switching element corresponding to a phase for which the magnitude of a current should be decreased is turned OFF in the time period corresponding to the next predetermined electrical angle.