Patent ID: 6111372
Filing Date: 2000-08-29
Classification: H02P

Abstract:
A sensorless motor driver comprising:a comparator circuit for producing square-wave signals by comparing back electromotive forces appearing in coils provided one for each phase in a brushless motor with a voltage at a node common to all of those coils;a masking circuit for performing masking on said square-wave signals in accordance with a noise masking signal;a masking signal producing circuit for producing said noise masking signal;a driving signal producing circuit for producing a driving signal from said square-wave signals masked by said masking circuit;a current supplying circuit for supplying a driving current to said brushless motor in accordance with said driving signal; andcurrent monitoring means for monitoring said driving current,wherein said masking signal producing circuit varies a length of masking periods within said noise masking signal according to a signal from said current monitoring means.