Patent ID: 7015663

Claim:
A brushless motor drive device comprising: a comparing circuit for comparing a drive signal and a reference signal to generate a pulse signal, the drive signal being associated with a rotation of a brushless motor and a frequency of the reference signal being higher than a frequency of the drive signal; a switching circuit coupled between a drive voltage source and the brushless motor and controlled by the pulse signal for driving the brushless motor; an adjusting circuit for adjusting a relative relationship between an amplitude of the drive signal and an amplitude of the reference signal in accordance with a current error signal representative of a difference between a current command signal and a motor drive current; and a limiting circuit having: a first circuit for generating a first-half duty-ratio limit signal; a second circuit for generating a second-half duty-ratio limit signal; a first logic circuit for constraining a duty ratio of the pulse signal by using the first-half duty-ratio limit signal and then generating an output signal; and a second logic circuit for constraining a duty ratio of the output signal of the first logic circuit by using the second-half duty-ratio limit signal.