Patent ID: 8471511

Claim:
A brushless motor control device comprising: a voltage application unit configured to cause each pair of switching elements connected to corresponding windings of a plurality of phases to apply a voltage to the corresponding windings of the phases in order to flow an electric current into the corresponding windings to generate a revolving magnetic field with a permanent magnet to rotate a magneto rotor of a brushless motor; an energization period derivation unit configured to detect rotation of the magneto rotor and to derive an energization period of the windings to generate the revolving magnetic field; a PWM signal generation unit configured to: generate a PWM signal at a duty ratio, which is controlled according to an inputted control signal, in the energization period derived by the derivation unit; generate a PWM signal at a duty ratio decreasing gradually in a predetermined time period subsequent to the energization period; and output the generated PWM signal for causing the voltage application unit to activate and deactivate the switching elements; and a detection period specifying unit configured to specify a detection period of the electric current flowing into the windings connected to the switching elements, which are presently switched and deactivated, by a time period, which is from a time point in advance of an edge of the PWM signal by a predetermined period to the edge, the edge being caused when the PWM signal changes to a different level to switch to deactivate the switching elements to control an electric current supplied to the windings; wherein the PWM signal generation unit is further configured to generate the PWM signal for switching activation and deactivation of the switching elements according to a comparison result between a count value, which is increased and decreased by count up and countdown repeatedly implemented in a predetermined range, and a first threshold, which is determined according to the control signal, the detection period specifying unit is further configured to, in a case where the PWM signal generation unit generates the PWM signal to activate the switching elements in a period in which the count value is greater than the first threshold, specify the detection period by a time period, in which the count value, which is implemented with count down in the predetermined range, is between the first threshold and a second threshold, which is greater than the first threshold, and the detection period specifying unit is further configured to, in a case where the PWM signal generation unit generates the PWM signal to activate the switching elements in a period in which the count value is less than the first threshold, specify the detection period by a time period, in which the count value, which is implemented with count up in the predetermined range, is between the first threshold and a third threshold, which is less than the first threshold.