Drive circuit for a brushless motor
First Claim
1. A drive circuit for a brushless motor of the type having a rotor magnet and energizable stator windings, said drive circuit comprising:
- position sensing means for sensing the rotary position of said rotor magnet and for generating varying position signals corresponding to said sensed rotary position; and
a plurality of amplifier means coupled to said position sensing means and responsive to said position signals to produce drive currents, said amplifier means being coupled to said stator windings to supply said drive currents thereto and each amplifier means including a voltage amplifier stage having a linear gain characteristic for amplifying the position signal applied thereto, a current amplifier stage coupled to said voltage amplifier stage and responsive to said amplified position signal to produce a drive current at an output thereof to supply same to a stator winding, and feedback means interconnected between the output of said current amplifier stage and an input to said voltage amplifier stage, said feedback means including a resistor and a capacitor connected in parallel and operative as a low pass filter circuit to prevent harmonics of the drive current frequency from being transmitted to said stator winding thereby preventing notching in said drive current.
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Accused Products
Abstract
A drive circuit for a brushless motor of the type having a rotor magnet and energizable stator windings. The drive circuit includes position sensors for sensing the rotary position of the rotor magnet and for generating varying position signals corresponding to the sensed rotary position. A plurality of amplifier stages is coupled to the position sensors, the amplifier stages being responsive to the position signals to produce drive currents which are supplied to the stator windings. In one embodiment, each amplifier stage includes a voltage amplifier having a linear gain characteristic for amplifying the position signal applied thereto, a current amplifier connected in cascade with the voltage amplifier and responsive to the amplified position signal to produce a drive current, and a feedback circuit interconnected between the output of the current amplifier and the input to the voltage amplifier, the feedback circuit including a resistor and a capacitor connected in parallel and operative as a low pass filter circuit to prevent harmonics of the drive current frequency from being transmitted to the stator winding, thereby preventing notching in the drive current.
In another embodiment, the drive circuit also includes a speed sensor for sensing the speed of the motor and for generating a signal whose frequency varies in accordance with the motor speed, a converter coupled to the speed sensor for converting the frequency of the generated signal to a voltage, a circuit for applying the converted voltage to the position sensors so as to modify the position signals in accordance with the sensed motor speed, and a circuit for supplying an offset voltage to the last-mentioned circuit such that if the speed of the motor exceeds a predetermined amount, the offset voltage exceeds the converted voltage whereby the resultant voltage which is applied to the position sensors causes a modification in the drive currents supplied to the stator windings, to produce an opposite torque in the motor. In this embodiment, excess motor speeds are rapidly corrected.
76 Citations
11 Claims
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1. A drive circuit for a brushless motor of the type having a rotor magnet and energizable stator windings, said drive circuit comprising:
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position sensing means for sensing the rotary position of said rotor magnet and for generating varying position signals corresponding to said sensed rotary position; and a plurality of amplifier means coupled to said position sensing means and responsive to said position signals to produce drive currents, said amplifier means being coupled to said stator windings to supply said drive currents thereto and each amplifier means including a voltage amplifier stage having a linear gain characteristic for amplifying the position signal applied thereto, a current amplifier stage coupled to said voltage amplifier stage and responsive to said amplified position signal to produce a drive current at an output thereof to supply same to a stator winding, and feedback means interconnected between the output of said current amplifier stage and an input to said voltage amplifier stage, said feedback means including a resistor and a capacitor connected in parallel and operative as a low pass filter circuit to prevent harmonics of the drive current frequency from being transmitted to said stator winding thereby preventing notching in said drive current. - View Dependent Claims (2, 3, 4)
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5. A drive circuit for a brushless motor of the type having a rotor magnet and energizable stator windings, said drive circuit comprising:
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speed sensing means for sensing the speed of said motor and for generating a signal whose frequency varies in accordance with said speed; converting means coupled to said speed sensing means for converting the frequency of said signal to a voltage, said converting means having a linear characteristic representing an inverse relation between said frequency and said voltage; current supply means for supplying drive currents to said stator windings to determine the torque of said motor; means for applying the voltage produced by said converting means to said current supply means to vary said drive currents as a function of the sensed speed of said motor; and means for supplying an offset voltage to said voltage applying means such that if the speed of said motor exceeds a predetermined amount, said offset voltage exceeds said converted voltage to modify said drive currents supplied to said stator windings so as to produce an opposite torque in said motor. - View Dependent Claims (6, 7, 8, 9, 10)
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11. A drive circuit for a brushless motor of the type having a rotor magnet and energizable stator windings, said drive circuit comprising:
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speed sensing means for sensing the speed of said motor and for generating a signal whose frequency varies in accordance with said speed; converting means coupled to said speed sensing means for converting the frequency of said signal to a voltage, said converting means having a linear characteristic representing an inverse relation between said frequency and said voltage; position sensing means for sensing the rotary position of said rotor magnet and for generating varying position signals corresponding to said sensed rotary position; a plurality of amplifier means coupled to said position sensing means and responsive to said position signals to produce drive currents, said amplifier means being coupled to said stator windings to supply said drive currents thereto and each amplifier means including a voltage amplifier stage having a linear gain characteristic for amplifying the position signal applied thereto, a current amplifier stage coupled to said voltage amplifier stage and responsive to said amplified position signal to produce a drive current at an output thereof to supply same to a stator winding, and feedback means interconnected between the output of said current amplifier stage and an input to said voltage amplifier stage, said feedback means including a resistor and a capacitor connected in parallel; means for applying the voltage produced by said converting means to said current supply means to vary said drive currents as a function of the sensed speed of said motor; and means for supplying an offset voltage to said voltage applying means such that if the speed of said motor exceeds a predetermined amount, said offset voltage exceeds said converted voltage to modify said drive currents supplied to said stator windings so as to produce an opposite torque in said motor.
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Specification