Patent ID: 6201657
Filing Date: 2001-03-13
Classification: G11B,H02P

Abstract:
A motor drive for driving a motor having three-phase coils in both a high rotation speed mode in which said motor rotates at a high rotation speed and a low rotation speed mode in which said motor rotates at a low rotation speed which is extremely lower than the high rotation speed, said motor drive comprising:a logic circuit for selectively producing, in response to a detected signal from a switch unit, one of a low speed selection signal and a high speed selection signal, said low speed selection signal being a signal indicative of making said motor rotate at the low rotation speed, said high speed selection signal being a signal indicative of making said motor rotate at the high rotation speed;a clock oscillator for oscillating a clock signal having a clock frequency;rotation speed detecting means for detecting a rotation speed of said motor to produce a speed detected signal;a phase-locked loop circuit connected to said logic circuit, said clock oscillator, and said rotation speed detecting means, said phase-locked loop circuit including a frequency divider for frequency dividing the clock signal, said frequency divider frequency dividing, in response to the low speed selection signal, the clock signal into a divided signal having a divided frequency corresponding to the low rotation speed, said frequency divider frequency dividing, in response to the high speed selection signal, the clock signal into the divided signal having the divided frequency corresponding to the high rotation speed, said phase-locked loop circuit detecting a phase difference between the speed detected signal and the divided signal to produce a control signal indicative of the phase difference;a speed switching device connected to a common connection terminal of said three-phase coils;a mode selection circuit connected to said logic circuit and said speed switching device, said mode selection circuit turning, in response to the low speed selection signal, said speed switching device off to make said three-phase coils the bipolar connection, said mode selection circuit turning, in response to the high speed selection signal, said speed switching device on to make said three-phase coils the unipolar connection, said mode selection circuit producing, in response to the low speed selection signal, a mode selection signal indicative of the low rotation speed mode, said mode selection circuit producing, in response to the high speed selection signal, the mode selection signal indicative of the high rotation speed mode; anda driving transistor, connected to said phase-locked loop circuit, said mode selection circuit, and said three-phase coils, for driving, on the basis of the control signal and the mode selection signal, said motor so that a frequency of the speed detected signal coincides with the divided frequency of the divided signal, thereby controlling a number of revolutions of said motor in each rotation speed mode in a stable manner and with high precision by using feedback control.