Double sampled phase detector circuit

A motor drive circuit for a three-phase motor, the motor drive circuit including a commutator arranged to provide a driving voltage to the motor from a DC voltage source which is a six-state commutator having three pairs of switches, each pair comprising an upper switch for connecting the DC voltage source to an individual one of three windings of the motor and a lower switch for connecting the one of three windings to the sensor, a sequencer operating the commutator to pulse width modulate the source voltage so that a motor current has a continuously variable wave form through the sequencer operating the commutator so that respective ones of the upper switches supplies source voltage to a respective winding during a respective 120° rotational phase of the motor, the sequencer further selectively operating up to two lower switches and up to upper switches from the pairs that do not include the operated upper switch to pulse width modulate the source voltage thereby generating the driving voltage, only one switch from a pair being operated at any one time, the sequencer being responsive to an error signal to align the driving voltage with the motor current wave form, and a phase detector supplying the error signal to the sequencer comprising:

• a sensor providing a sense voltage representative of the motor current;
• a first sample circuit providing a plurality of first samples of respective instantaneous values of the sense voltage which includes a first sample switch and a first capacitor, the first sample switch operating during a plurality of intervals during a motor phase to store voltages in the first capacitor representative of successive instantaneous values of the sense voltage;
• a second sample circuit providing a second sample of a selected instantaneous value of the sense voltage which includes a second sample switch and a second capacitor, the second sample switch operating during a single interval during the motor phase to store a voltage in the second capacitor representative of a selected instantaneous value of the sense voltage;
• and
• an error generation circuit providing the error signal based on a difference between the second sample and each of the plurality of first samples.

A motor drive circuit for a three-phase motor, the motor drive circuit including a commutator arranged to provide a driving voltage to the motor from an DC voltage source, a sequencer operating the commutator to pulse width modulate the source voltage so that a motor current has a continuously variable wave form, the sequencer being responsive to an error signal to align the driving voltage with motor current wave form, and a phase detector supplying the error signal to the sequencer comprising:

• a sensor providing a sense voltage representative of the motor current;
• a first sample circuit providing a plurality of first samples of respective instantaneous values of the sense voltage through the sequencer operating a first sample switch for a plurality of intervals during each motor phase;
• a second sample circuit providing a second sample of a selected instantaneous value of the sense voltage through the sequencer operating a second sample switch during one of the intervals during each motor phase that the first sample switch is operated;
• and
• an error generation circuit providing the error signal based on a difference between the second sample and each of the plurality of first samples.

A method of operating a three-winding motor comprising:

• commutating a DC voltage to provide a driving voltage having a voltage phase, the windings of the motor generating a continuously variable driving current;
• sensing a voltage representative of motor current while providing the driving voltage to one winding of the motor, the motor current having a current phase;
• sampling plurality of instantaneous values of the sensed voltage;
• selecting one of the sampled instantaneous values;
• deriving an error signal based on a difference between the selected one value and each of the plurality of values;
• and
• adjusting the voltage phase based on the error signal to align the voltage phase with the current phase.