Patent ID: 7230785

Claim:
A drive control device of a motor comprising: a current output circuit that sequentially makes a current flow to a coil of each of phases in a brushless motor provided with a plurality of coils; a coil voltage detection circuit that detects a voltage across coil terminals of each of the phases of the brushless motor; a coil current detection circuit that detects currents flowing through coils of the brushless motor; an analog-to-digital converter that converts the voltage across the coil terminals detected by the coil voltage detection circuit and the currents flowing through the coils detected by the coil current detection circuit into digital signals; and a control system circuit that controls the current output circuit based on signals detected by the coil voltage detection circuit and the coil current detection circuit, the drive control device driving to rotate the motor by sequentially switching the currents flowing through the coils of the brushless motor, wherein the control system circuit comprises: a phase difference detector that detects phase differences between zero crossing points of back electromotive forces of the coils detected by the coil voltage detection circuit during rotation of the motor, and zero points of the currents outputted from the current output circuit; a filter that accumulates the phase differences detected by the phase difference detector; an oscillator of which frequencies are controlled according to outputs from the filter; and an output current control circuit that drives the current output circuit and generates signals for controlling output currents from the current output circuit, wherein output signals from the oscillator are supplied to the output current control circuit as signals that give switching timing of the current flowing through the coil of each of the phases, and signals that give timing of zero crossing points of the output currents are fed back to the phase difference detector from the output current control circuit, to form a phase control loop, and wherein a rotational speed comparator is provided which compares a rotational speed extracted from a digital signal which contains information on a rotational speed of the brushless motor and is taken out on the way of the phase control loop with a target rotational speed to thereby detect a rotational speed error, and the output current control circuit controls the rotational speed of the brushless motor based on an output from the rotational speed comparator.