Amplifier and method for detecting the bemf of a coil of a polyphase sensorless DC motor

Claim 2

A circuit for detecting a back emf signal of a motor coil, comprising: circuitry for providing a differential voltage proportional to the back emf of the motor coil; circuitry for adding a first hysteresis bias current to said circuitry for providing a differential voltage, to modify the produced differential voltage; circuitry for adding a second hysteresis bias current to said circuitry for providing a differential voltage, to modify the produced differential voltage responsive to the back emf approaching a zero crossing from a predetermined direction, said second hysteresis bias current opposing and of greater magnitude than said first hysteresis bias current; and a comparator connected to receive the modified differential voltage to produce an output state change when the modified differential voltage exceeds a predetermined value.

Claim 3

The circuit of claim 1 wherein said motor coil is one of a plurality of motor field coils connected in a "Y" configuration.

Claim 4

The circuit of claim 1 wherein the magnitude of said second hysteresis bias current is twice as large as the magnitude of said first hysteresis bias current.

Claim 5

The circuit of claim 1 wherein said circuitry for adding a second hysteresis bias current is coupled to said comparator, so that the second hysteresis bias current is added responsive to the output of said comparator being low.

Claim 6

The circuit of claim 4 wherein the magnitude of said second hysteresis bias current is twice as large as the magnitude of said first hysteresis bias current.

Claim 7

A circuit for detecting a back emf signal of a motor coil for use in determining a position of the rotor of the motor, comprising: a comparator; first and second current paths each comprising a current control element and at least one resistor element on which a voltage is developed in response to a current in the current path, the voltage on each resistor element being connected to respective inputs of said comparator; one end of said motor coil being connected to said current control element of said first current path, and a reference potential being connected to said current control element of said second current path, whereby the back emf signal across said coil produces a change in voltage across the resistor element of said first current path with respect to the voltage across the resistor element of said second current path; means for selectively producing a first signal during detection of the back emf signal developed in said motor coil when the back emf signal approaches a zero crossing from a predetermined direction; means for biasing said first current path with a preset bias current; means for switchably biasing said second current path with an increased preset bias current; and a switch operative in response to said first signal to switchably apply the increased preset bias current to said second current path, said comparator producing an output state change when the back emf signal of said motor coil exceeds a value determined by said preset bias current.

Claim 8

A circuit for detecting a back emf signal of a motor coil for use in determining a position of the rotor of the motor, comprising: a comparator; first and second current paths each comprising a current control element and at least one resistor element on which a voltage is developed in response to a current in the current path, the voltage on each resistor element being connected to respective inputs of said comparator; one end of said motor coil being connected to said current control element of said first current path, and a reference potential being connected to said current control element of said second current path, whereby the back emf signal across said coil produces a change in voltage across the resistor element of said first current path with respect to the voltage across the resistor element of said second current path; means for selectively producing a first signal during detection of the back emf signal developed in said motor coil when the back emf signal approaches a zero crossing from a predetermined direction; means for biasing said first current path with a preset bias current; means for switchably biasing said second current path with an increased preset bias current; and a switch operative in response to said first signal to switchably apply the increased preset bias current to said second current path, said comparator producing an output state change when the back emf signal of said motor coil exceeds a value determined by said preset bias current.

Claim 9

The circuit of claim 6 wherein said comparator has an inverting input and a noninverting input operative to produce a change in output state when a voltage applied to the inverting input exceeds a voltage applied to the noninverting input, said voltage across said resistor element in said first current path being connected to the inverting input of said comparator, and said voltage across said resistor element in said second current path being connected to the noninverting input of said comparator.

Claim 10

The circuit of claim 6 wherein said motor coil is one of a plurality of motor field coils connected in a "Y" configuration, and said reference potential connected to said current control element of said second current path is produced at a center tap connection of said plurality of motor field coils.

Claim 11

The circuit of claim 6 wherein said means for switchably biasing said second current path with an increased preset bias current comprises means for switchably biasing said second current path with a bias current of twice said preset bias current.

Claim 12

The circuit of claim 6 wherein said current control element of each of said first and second current paths is a bipolar transistor.

Claim 13

The circuit of claim 6 wherein said resistor element of each of said first and second current paths is an FET.

Claim 14

The circuit of claim 9 wherein said FETs of said first and second current paths have equal resistance.

Claim 15

The circuit of claim 6 wherein said current control element of each of said first and second current paths is a bipolar transistor, and wherein said resistor element of each of said first and second current paths is a pair of FETs, the current paths of said bipolar transistor and said FETs being connected in series, the output voltage being developed between said bipolar transistor and one of said FETs and the bias current being connected between said FETs.

Claim 16

The circuit of claim 6 further comprising: means for biasing said second current path with a hysteresis bias current; means for switchably biasing said first current paths with an increased hysteresis bias current; and a switch operative in response to the output of said comparator to switchably apply the increased hysteresis bias current to said first current path.

Claim 17

The circuit of claim 6 wherein said means for switchably biasing said first current path with an increased hysteresis bias current comprises means for switchably biasing said first current path with a bias current of twice said hysteresis bias current.

Claim 18

The circuit of claim 6 further comprising means for switchably applying a bias current to both said first and second current paths, and means for generating a signal when said motor coil is floating for actuating said means for switchably applying a bias current.

Claim 19

A back emf signal amplifier for amplifying a back emf signal of a field coil of a polyphase sensorless dc motor, comprising: a comparator; first and second balanced current paths, each current path comprising: a transistor having a current path, and two resistive elements, said current path of said transistor and said two resistive elements being connected in series with said current path and one of said two resistive elements being connected at a first node, and said two resistive elements being connected at a second node; the first node of said first current path and the first node of said second current path being connected to respective inputs of said comparator; one end of said field coil being connected to a control terminal of said transistor of said first current path, and a reference potential being connected to a control terminal of said transistor of said second current path, whereby the back emf signal across said field coil produces a change in voltage at said first node of said first current path with respect to the voltage on the fist node of said second current path; a circuit for selectively producing a first signal during detection of the back emf signal developed in said field coil when the back emf signal approaches a zero crossing from a predetermined direction; circuitry for biasing said first current path with a preset bias current connected to said second node of said first current path; circuitry for switchably biasing said second current path with an increased preset bias current connected to said second node of said second current path; a switch operative in response to said first signal to switchably apply the increased preset bias current to said second current path, said comparator producing an output state change when the back emf signal of said motor coil exceeds a value determined by said preset bias current; circuitry for biasing said second current path with a hysteresis bias current connected to said second node of said second current path; circuitry for switchably biasing said first current path with an increased hysteresis bias current connected to said second node of said first current path; and a switch operative in response to the output state change of said comparator to switchably apply the increased hysteresis bias current to said first current path.

Claim 20

A back emf signal amplifier for amplifying a back emf signal of a field coil of a polyphase sensorless dc motor, comprising: a comparator; first and second balanced current paths, each current path comprising: a transistor having a current path, and two resistive elements, said current path of said transistor and said two resistive elements being connected in series with said current path and one of said two resistive elements being connected at a first node, and said two resistive elements being connected at a second node; the first node of said first current path and the first node of said second current path being connected to respective inputs of said comparator; one end of said field coil being connected to a control terminal of said transistor of said first current path, and a reference potential being connected to a control terminal of said transistor of said second current path, whereby the back emf signal across said field coil produces a change in voltage at said first node of said first current path with respect to the voltage on the fist node of said second current path; a circuit for selectively producing a first signal during detection of the back emf signal developed in said field coil when the back emf signal approaches a zero crossing from a predetermined direction; circuitry for biasing said first current path with a preset bias current connected to said second node of said first current path; circuitry for switchably biasing said second current path with an increased preset bias current connected to said second node of said second current path; a switch operative in response to said first signal to switchably apply the increased preset bias current to said second current path, said comparator producing an output state change when the back emf signal of said motor coil exceeds a value determined by said preset bias current; circuitry for biasing said second current path with a hysteresis bias current connected to said second node of said second current path; circuitry for switchably biasing said first current path with an increased hysteresis bias current connected to said second node of said first current path; and a switch operative in response to the output state change of said comparator to switchably apply the increased hysteresis bias current to said first current path.

Claim 21

The circuit of claim 17 wherein said field coil is one of a plurality of motor field coils connected in a "Y" configuration, and said reference potential connected to said transistor of said second current path is produced at a center tap connection of said plurality of motor field coils.

Claim 22

The circuit of claim 17 wherein said means for switchably biasing said second current path with an increased preset bias current comprises means for switchably biasing said second current path with a bias current of twice said preset bias current.

Claim 23

The circuit of claim 17 wherein said two resistive elements of each of said first and second current paths are FETs.

Claim 24

The circuit of claim 17 wherein said means for switchably biasing said first current path with an increased hysteresis bias current comprises means for switchably biasing said first current path with a bias current of twice said hysteresis bias current.

Claim 25

The circuit of claim 17 further comprising means for switchably applying a bias current to both said first and second current paths, and means for generating a signal when said motor coil is floating for actuating said means for switchably applying a bias current.

Claim 26

The circuit of claim 17 wherein said comparator has an inverting input and a noninverting input operative to produce a change in output state when a voltage applied to the inverting input exceeds a voltage applied to the noninverting input, said first node of said first current path being connected to the inverting input of said comparator, and the first node of said second current path being connected to said noninverting input of said comparator.

Claim 27

The circuit of claim 17 wherein said two resistor elements of said first and second current paths are resistors.

Claim 30

The method of claim 22 wherein said step of switchably adding a second fixed bias voltage higher than said first fixed bias voltage to said first voltage comprises switchably adding a bias voltage two times higher than said first fixed bias voltage.

Claim 31

The method of claim 25 further comprising: adding a first hysteresis bias voltage to said first voltage; and in response to the output voltage, switchably adding a second hysteresis bias voltage higher than said first hysteresis bias voltage to said second voltage.

Claim 32

The method of claim 27 wherein said step of switchably adding a second hystereis bias voltage higher than said first hysteresis bias voltage comprises switchably adding a bias voltage two times higher than said first hysteresis bias voltage.

Claim 35

The method of claim 29 wherein said step of switchably adding a second fixed bias voltage larger than said first fixed bias voltage to said differential voltage comprises switchably adding a bias voltage two times larger than said first fixed bias voltage.

Claim 36

The method of claim 29 further comprising: adding a first hysteresis bias voltage to said differential voltage proportional to a voltage on said motor coil, in response to the output voltage, switchably adding a second hysteresis bias voltage higher than said first hysteresis bias voltage and of opposite polarity to said differential voltage.

Claim 37

The method of claim 31 wherein said step of switchably adding a second hystereis bias voltage higher than said first hysteresis bias voltage comprises switchably adding a bias voltage two times higher than said first hysteresis bias voltage.