Patent ID: 7126301

Claim:
A motor driver comprising: plural-phase windings; a plurality of transistors composed of a first group of transistors that operate as switches for supplying power from one terminal of a DC power unit to one end of each winding, and a second group of transistors that operate as switches for supplying power from another terminal of the DC power unit to another end of each winding; a position detector operable to detect a rotational position of a rotor, based on a terminal voltage of each winding; a current detector operable to output a current detection signal that is proportionate to a current supplied to the plural-phase windings; a switching controller that includes a forced-off signal generator operable to generate a forced-off signal that has a pulse width of a predetermined duration in a predetermined cycle that corresponds at least to a clock, and a PWM signal generator operable to generate a basic PWM signal in accordance with a result of comparing the current detection signal and a speed command signal, and is operable to generate a PWM signal by AND synthesizing the forced-off signal with the basic PWM signal; and a power distributor operable to generate first power distribution signals that correspond to a result of detection by the position detector, generate second power distribution signals by AND synthesizing a power distribution signal that corresponds to a result of detection by the position detector with the PWM signal from the switching controller, and output the generated first power distribution signals and the generated second power distribution signals, thereby causing the plurality of transistors to perform switching operation, wherein the switching controller further controls such that upper and lower transistors which switch the plural-phase windings are forced into a compulsory OFF state by means of the forced-off signal included in the PWM signal, and the position detector detects only while the upper and lower transistors are in the compulsory OFF state.