Patent ID: 6922029

Claim:
A DC motor driver for driving a DC motor in which hall elements are mounted by shifting, with respect to a stator, a mounting position of the hall elements for detecting a position of a rotor, comprising: an FG pattern for outputting a pulse wave of a period proportional to a number of revolutions of the DC motor, an FG amplifier for producing an FG signal proportional to the number of revolutions of the DC motor on the basis of the output of the FG pattern, a speed discriminator circuit for comparing a period of the FG signal with a preset period to output a signal corresponding to an error in the number of revolutions of the DC motor, a charge pump circuit for converting the output of the speed discriminator circuit into DC voltage, a first hall amplifier for amplifying the amplitude of output voltage of the hall elements so as to be proportional to the DC voltage of the charge pump, a second hall amplifier for producing a rectangular wave on the basis of the output voltage of the hall elements, an F/V converter for converting the frequency of the FG signal into DC voltage, selecting means for selecting the first hall amplifier when output voltage of the F/V converter is equal to or more than a preset threshold voltage, and selecting the second hall amplifier when the output voltage of the F/V converter is less than the preset threshold voltage, a PWM comparator for producing a power-on pattern for switching the driving of the DC motor by comparing the output voltage of the first hall amplifier or the second hall amplifier selected by the selecting means with a reference triangular wave for PWM modulation, and current amplification transistors for supplying current to windings of the DC motor in accordance with the output of the PWM comparators.