Brushless motor control circuit

Abstract

According to the present invention, control is performed to set a constant difference between two phase inputs among three phase inputs to a three-phase brushless motor. As a result, imbalance between the respective phase inputs (signals) is eliminated, thus performing motor control with good rotational precision. According to the present invention, amplifiers (1.sub.1 -1.sub.3, 2.sub.1 -2.sub.3, 3.sub.1 -3.sub.3) for receiving rotor position detection signals of the motor are provided in common to the three-phase input lines of the three-phase brushless motor. One of the difference and the sum of a product of two phases signals, among three phase outputs from these amplifiers, and a signal as the square of the remaining phase signal is compared with a constant value. A comparison result signal is fed back to the amplifiers (1.sub.1 -1.sub.3, or 2.sub.1 -2.sub.3, or 3.sub.1 -3.sub.3) of a common stage of the three-phase input lines to control the rotation of the motor. The product of the two phase signals is obtained by a multiplier (11). The square of the remaining one phase signal is obtained by a square multiplier (12). One of the sum and the difference of the product and the square signals is obtained by an arithmetic unit (13 or 13.sub.1). The arithmetic unit output and the constant value are compared by a comparator (14).

Dependencies are inferred from the claim text.