Abstract: A drive circuit for a brushless motor having a rotor formed of a permanent magnet and stator coils includes a plurality of magnetic sensors each for sensing a rotational position of the rotor of the brushless motor to generate a voltage signal in accordance with a magnitude of a magnetic flux density received from the rotor passing, power amplifiers each for converting the voltage signal from each corresponding magnetic sensor to a drive voltage having a predetermined phase and voltage value and supplying the drive voltage obtained to each corresponding stator coil, a speed control signal generating circuit for generating a speed control signal for control of the rotational speed of the brushless motor, and magnetic sensor controller for controlling the magnitude of the output voltage of each magnetic sensor in response to the speed control signal so that the output voltage of each magnetic sensor takes a value in accordance with the speed control signal.

Abstract: An image forming apparatus includes a scanner for scanning a light beam over an image carrier, an image forming unit for forming an image on the image carrier corresponding to the light beam scanned over the image carrier by the scanner and a movable supporting member for supporting an image forming medium and conveying the image forming medium to a position where the image on the image carrier is transferred to the image forming medium.

Abstract: A drive circuit for a brushless motor includes position detectors for detecting a rotational position of a rotor of the brushless motor, thereby generating position detection signals. A plurality of amplifiers have respective transistors at least in its output stage and feed an electric power to stator windings of the brushless motor through the transistors of the output stage in a timing in accordance with the position detection signals from the position detectors respectively. Each amplifier has an amplification degree varied based on a speed control signal. A voltage detector detects an output voltage of each amplifier. A power supply adjusting device controls a power supply voltage applied to each amplifier based on a detection voltage of the voltage detector.