Abstract: A spindle motor for a disc drive, such as a CD-ROM drive, is provided. This spindle motor is a brushless motor of a single-phase axial-winding and radial-gap type including a stator, a rotor coupled to said stator, and a driving circuit for supplying a driving signal to the stator to rotate the rotor. The stator includes a pair of upper and bottom salient-pole pieces formed with a plurality of tooth-like portions serving as salient-poles. The peak surface of each tooth-like portion is formed into a symmetrical convex shape, which minimizes the cogging torque of the motor. Further, the use of a phase-adjuster in the driving circuit allows the motor to produce large output torque at high speeds. The output characteristics of this spindle motor meet the requirements of high speed CD-ROM drives.

Abstract: An automatic phase adjuster for the driver of a brushless motor is provided. This automatic phase adjuster can output a driving signal adaptively with a suitable phase-lead or phase-lag angle so as to allow the motor to be operated with the optimal output characteristics, including optimal output torque, optimal output efficiency, and optimal output power at all speeds. The automatic phase adjuster is configured variously in accordance with the particular type of the motor on which the automatic phase adjuster is used. For single-direction motors operated at a fixed speed, the automatic phase adjuster includes a phase-lead filter coupled to a Hall sensor which detects the motor speed. For single-direction motors operated at various speeds, the automatic phase adjuster includes a phase-lead filter, a phase-lag filter, a multiplexer, and a Hall sensor. The multiplexer selects either the phase-lead filter or the phase-lag filter to process the motor speed signal.

Abstract: A brushless motor stator for an axially wound brushless motor with a diametrical air-gap having a plate structure with at least one plate, the profile of the plate comprising: a central circular hole; a number of salient poles surrounding the central circular hole; and a slot opening between every two adjacent said salient poles. The salient poles and those slot openings have the following characteristics: (1) the outer rim of the salient pole is in the form of a circular arc segment whose arc radius R.sub.S satisfies the following inequality relation: .pi./P.times.R.sub.M <R.sub.S <0.95R.sub.M ; (2) the neck width W.sub.S of the salient pole satisfies the following inequality relation: .pi./2P.times.R.sub.M <W.sub.S <2.pi./P.times.R.sub.M -g; (3) the depth D.sub.S of the slot opening satisfies the following inequality relation: .pi./P.times.R.sub.M <D.sub.S <2.5.pi./P.times.R.sub.M ; where R.sub.