Patent ID: 7573226

Claim:
A drive circuit for an AC motor, the AC motor comprising a combination of a coil body and a permanent magnet, and a pair of Hall element sensors, the coil body having a plurality of coils, the permanent magnet having a plurality of magnet pole elements, the plurality of magnet pole elements being arranged to become alternating opposite poles to rotate relative to the coil body, and each of the Hall element sensors being positioned at a different location and provided to detect magnetic alternation in accordance with a relative movement between the coil body and the permanent magnet and to output an analog signal corresponding to a waveform having a pattern of a back electromotive force voltage generated in the coil body, the drive circuit comprising: a first unit constituted to output a reference level; a second unit constituted to compare the analog signal output by the Hall element sensors with the reference level output by the first unit; and a third unit constituted to generate and output a drive signal to the coil body by switching a voltage based on results of a comparison by the second unit, wherein the first unit outputs an upper level and a lower level as the reference level, wherein the second unit compares the analog signal with both the upper level and the lower level, and wherein the third unit generates a pair of the drive signals, each drive signal respectively corresponding to results of the comparison for either the upper level or the lower level.