Motor drive circuit

Abstract

A full wave signal E is compared with a trapezoidal wave signal G in a comparator to output a second comparison signal H. The full wave signal E is obtained through full wave conversion applied to a sine wave signal of a Hall element. The trapezoidal wave signal G is obtained by sampling and holding an attenuated signal F, obtained by attenuating the full wave signal E, at a trailing end of a first comparison signal D, and nulling the attenuated signal F at a subsequent leading end thereof. Then, the first and second comparison signals D, H are added up in an OR circuit to output an addition signal K, so that no drive current IL flows through the driving coils at a point near the former and latter halves of a phase changeover point. Near the former half of a phase changeover a point, the drive current IL is nulled before counter electromotive force Ec becomes small, enabling motor noise reduction. Near the latter half of a phase changeover point, the drive current IL remains zero, continuously from the former half, preventing a drop of efficiency in driving a motor. Since a trapezoidal wave signal G is made from the attenuated signal F, a period with the drive current IL being zero is always ensured near the former half of a phase changeover point.