PURPOSE: A constant-power brushless DC motor is provided to separately control DC motors according to a surface magnet type and a buried magnet type by forming a rotor in which a permanent magnet is buried inside of laminated silicon steel plates. CONSTITUTION: A rectifier encoder(600) is formed by mounting sensors on a detection region(606). The rectifier encoder is comprised of a sensor plate(604) and a circle plate(602) in which a non-detection region is included. The non-detection region and the detection region of the circle plate are determined according to a rotator pole number and a stator constant number. Each phase is operated by being connected to the rectifier encoder. A pair of optical sensors(PA1,PA2) is installed on the sensor plate of the rectifier encoder in a predetermined mode.
