Brushless motor

Abstract

To further improve the stability of drive control for the start period of a motor without complicating a circuit configuration. During the period in which the rotational speed of a rotor does not reach the rotational speed capable of locking a PLL circuit, a drive control method of two-phase mode in which a start current is supplied by two energizing patterns is used. In energizing pattern A, a current is caused to flow in a motor winding in the direction from U to W and in the direction from V to W at the same time. In energizing pattern B, a current is caused to flow in the motor winding in the direction from W to U and in the direction from W to V at the same time. A potential difference Vbetween a U phase and a V phase in which the phase and magnitude of voltage drop due to inductance are equal is detected. Based on the detected potential difference V, a magnetic flux estimation signal φis calculated by an integrator. Then, based on the magnetic flux estimation signal φ, an ROT signal is sent from a comparator. The energizing pattern of the start current is switched over according to the ROT signal, and torque in the normal rotation direction is developed, by which the rotor is accelerated.