Abstract: A driving apparatus of a sensorless brushless motor includes an inverter circuit supplying a power supply voltage, of which duty ratios is variably controlled by a pulse-width modulation method, a PWM generator circuit generating a pulse-width modulation signal, a position detection circuit operating at a predetermined phase of the pulse-width modulation signal and detecting a rotational position of the rotor, and an inverter control circuit transmitting an energization control signal determined based on the pulse-width modulation signal to the inverter circuit. The PWM generator circuit provides a stepwise increase and decrease of a pulse-width modulation frequency in a normal PWM frequency, a low-speed PWM frequency, and a high-speed PWM frequency in response to an increase and decrease of one of following parameters; the commanded duty ratio, the commanded number of rotations of the motor, a detected duty ratio, and a detected number of rotations of the motor.

Abstract: A driving apparatus of a sensorless brushless motor includes an inverter circuit supplying a power supply voltage to three phase terminals of three phase armature windings of the sensorless brushless motor provided with a stator and with a rotor including a pair of magnetic poles, a PWM generator circuit generating a pulse-width modulation signal, a position detection circuit operating at a particular phase of the pulse-width modulation signal, detecting an induced voltage induced at the terminal that is in a non-energization time zone and detecting a rotational position of the rotor, an inverter control circuit determining an energization time zone and transmitting an energization control signal to the inverter circuit, and a PWM delay circuit generating a pulse-width modulation signal for position detection by delaying the pulse-width modulation signal, wherein the position detection circuit operates at a particular phase of the pulse-width modulation signal for position detection.