Patent ID: 8704470

Claim:
A motor driving circuit configured to receive a Hall signal, which comprises a first signal and a second signal that are complementary, from a Hall sensor, and to PWM (Pulse Width Modulation) drive a motor, the motor driving circuit comprising: a control instruction combining circuit configured to generate a duty ratio control signal which indicates a duty ratio for the PWM driving operation based upon first digital data which indicates the duty ratio for the PWM driving operation and second digital data which indicates the temperature; a pulse modulator configured to convert the duty ratio control signal into a pulse control signal having the duty ratio indicated by the duty ratio control signal; and a driver circuit configured to drive the fan motor based upon the pulse control signal, wherein the control instruction combining circuit comprises: a first calculation unit configured to subtract third digital data which indicates the minimum value of the duty ratio from the first digital data; a slope calculation unit configured to generate temperature-dependent slope data based upon the second digital data; a second calculation unit configured to multiply the slope data by the output data of the first calculation unit; a third calculation unit configured to sum the output data of the second calculation unit and the third digital data; and a selector configured to receive the output data of the third calculation unit and the third digital data, to select data that corresponds to the sign of the output data of the first calculation unit, and to output the data thus selected as the duty ratio control signal.