Motor driver and motor drive method

A motor driver having a plurality of output circuits each including an upper side switching element and a lower side switching element connected in series, for supplying a current to a motor from a connection point between the upper side switching element and the lower side switching element of each output circuit, 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 of the plurality of output circuits according to the position signal and turning ON the selected switching element for a time period corresponding to a predetermined electrical angle, and switching lower side switching elements of a plurality of output circuits among the remaining ones of the plurality of output circuits when the selected switching element is an upper side switching element while switching upper side switching elements of a plurality of output circuits among the remaining ones of the plurality of output circuits when the selected switching element is a lower side switching element;
• and
• an ON-period control section for generating a switching control signal for controlling the switching operation by the phase switch circuit according to an input torque command signal and a voltage generated at the current detection resistance so that each of a plurality of periods obtained by dividing the time period corresponding to the predetermined electrical angle includes a first period in which a plurality of switching elements among the switching elements to be switched are turned ON and a second period in which one of the plurality of switching elements turned ON in the first period is kept ON, and outputting the generated signal.