Disclosed is a spindle motor for hard disk drives capable of generating mechanical and electrical preloads to form a predetermined sized air gap through use of mechanical and electrical offsets, so that the spindle motor is prevented from being damaged by friction and heat generated during an initial starting. The spindle motor with mechanical and electrical offsets is designed so that a midpoint of the vertical width of the poles wound around by a coil of a stator is placed within a magnetic field so as not to be flush with a midpoint of the vertical width of a permanent magnet fitted on the inner circumferential surface of the hub, and each of the poles has at least one of its upper and lower end extending in a vertical direction by a predetermined length to distribute magnetic flux density differently between the upper and lower ends of each pole.

Disclosed is a multiphase brushless DC motor of a concentrated winding type having shunt connection, and a control circuit. The brushless DC motor includes a rotor made up of a permanent magnet with M number of poles, and a stator operating in K number of phases by means of windings wound on N number of teeth, wherein the plurality of windings having the same excitation phases wound on the teeth, are each maintained in shunt connection so as to improve driving torque and a rotational speed. A brushless DC motor includes a switching section having a plurality of upper switching devices and a plurality of lower switching devices connected with each other in series. Each of the windings is connected between a common joint between the upper and lower switching devices, and a common joint between a lower power supply voltage and a plurality of upper power supply voltages.