Apparatus and method of regulating the speed of a DC brushless motor
AssigneeNidec America Corporation
InventorGeorge H. Harlan
Life of this patent
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Abstract
A control circuit for regulating the rotational speed of a DC brushless motor includes an electrical conduction switch having an input, an output and a control terminal for passing a motor supply signal to a DC brushless motor. A voltage averaging circuit generates an averaged signal indicative of the average voltage level being supplied to the motor. The averaging circuit informs an error amplifier to modulate the motor supply signal to compensate for changes in the voltage level of the motor supply signal in order to maintain the rotational speed of the motor at a generally constant rpm. The control circuit takes advantage of the motor windings and rotor mass as a filter circuit to smooth changes in current drawn by the motor, and to further maintain the rotational speed of the motor.
Claims20
A voltage-feedback control circuit for regulating the rotational speed of a DC brushless motor having at least one input terminal, and a motor winding electrically coupled to the at least one input terminal, the voltage-feedback control circuit comprising:
- an electrical conduction switch having an input, an output and a control terminal for passing a motor supply signal to the DC brushless motor from a voltage across first and second terminals of a DC voltage source, the input terminal of the switch being coupled to the first terminal of the DC voltage source, and the output terminal of the switch being coupled to the at least one input terminal of the motor and defining a substantially inductorless connection therebetween to thereby allow the motor windings to serve as an inductive filter to smooth changes in the motor current;
- a differential (error) amplifier having first and second input terminals and an output terminal for generating a differential signal having a voltage level indicative of the difference between a voltage level corresponding to the motor supply signal and a reference voltage, the first input terminal of the differential amplifier being coupled to a voltage reference, and the second input terminal of the differential amplifier being coupled to the output terminal of the switch;
- and
- a pulse-width modulator (pwm) having an input terminal and an output terminal, the input terminal of the pwm being coupled to the output terminal of the differential amplifier and the output terminal of the pwm being coupled to the control terminal of the switch, such that the pwm generates a modulator signal having a pulse width indicative of the voltage level of the differential signal to turn the switch on and off to modulate the motor supply signal and generate a substantially constant selected voltage level to the motor supply signal.
A voltage-feedback control circuit for regulating the rotational speed of a DC brushless motor having at least one input terminal, and a motor winding electrically coupled to the at least one input terminal, the voltage-feedback control circuit comprising:
- first means coupled to an electrical power source for switchably passing a motor supply signal to the at least one input terminal of the DC brushless motor and defining a substantially inductorless connection therebetween for allowing the motor windings to serve as an inductive filter to smooth changes in the motor current;
- second means coupled to an output of the first means for generating a differential signal having a voltage level indicative of the difference between a voltage level corresponding to the motor supply signal and a reference voltage;
- and
- third means for turning, on and off the first means in response to the value of the differential signal in order to provide a substantially constant selected motor supply voltage level.
A method of regulating the rotational speed of a DC brushless motor having at least one input terminal, and a motor winding electrically coupled to the at least one input terminal, comprising the steps of:
- passing motor supply signals from an electrical power source through an electrical conduction switch having an input, an output, and a control terminal, and through a substantially inductorless path extending between the output terminal and the at least one input terminal of the DC brushless motor to thereby allow the motor windings to serve as an inductive filter to smooth changes in the motor current;
- generating a differential signal having a voltage level indicative of the difference in voltage between a voltage level corresponding to at least one motor supply signal and a reference voltage;
- and
- modulating the step of passing the motor supply signal in response to the value of the differential signal to provide a substantially constant voltage level of the motor supply signal.
Dependencies are inferred from the claim text.