Current injection circuit for delaying the full operation of a power factor control circuit for AC induction motors

An energy saver delay circuit for an induction motor, comprising:

• a power factor control circuit including an integrator having a negative summing junction;
• and a current injection circuit electrically connected to the negative summing junction, wherein the current injection circuit injects offset current into the negative summing junction to cause about the maximum available voltage from a power source, coupled to the negative summing junction, to be supplied to the motor for a predetermined amount of time;
• a current sensing resistor configured to sense the current through the motor, wherein the current injection circuit comprises:
• an amplifier circuit configured to measure the voltage across the current sensing resistor and to convert the sensed current to an amplified voltage;
• a half-wave rectifier circuit electrically connected to an output of the amplifier circuit and configured to output a first value when the amplified voltage is of one polarity, and to output a second value when the amplified voltage is of another polarity;
• a comparator circuit electrically connected to an output of the positive half-wave rectifier circuit and configured to square an output waveform of the positive half-wave rectifier circuit responsive to the current though the motor exceeding the predetermined threshold current;
• and a programmable timer electrically connected to an output of the comparator circuit, the programmable timer including a current injection resistor between the programmable timer and the negative summing junction, and
• wherein the current injection circuit is triggered by current flowing through the motor, responsive to the current exceeding a predetermined threshold current.

An energy saver delay circuit for an induction motor, comprising:

• a power factor control circuit including an integrator having a negative summing junction;
• and a current injection circuit electrically connected to the negative summing junction, wherein the current injection circuit injects offset current into the negative summing junction to cause about the maximum available voltage from a power source, coupled to the negative summing junction, to be supplied to the motor for a predetermined amount of time;
• wherein the current injection circuit further comprises:
• a half-wave rectifier circuit electrically connected across the power factor control circuit and configured to rectify an AC voltage across the power factor control circuit and to reduce the peak voltage to within the operating voltage range of the current injection circuit;
• a comparator circuit electrically connected to an output of the half-wave rectifier circuit and configured to square an output waveform of the half-wave rectifier circuit responsive to the voltage across the power factor control circuit exceeding the predetermined threshold voltage;
• and a programmable timer electrically connected to an output of the comparator circuit, the programmable timer including a current injection resistor between the programmable timer and the negative summing junction, and
• wherein the current injection circuit is triggered by voltage across the power factor control circuit, responsive to the voltage exceeding a predetermined threshold voltage.

A power factor control circuit for an induction motor, comprising:

• a voltage/current phase difference generator for determining a difference in phase between a voltage applied to the motor and a current drawn by the motor, and for generating a phase difference signal as a function of the determined difference in phase, the voltage/current phase difference generator including an integrator, the integrator receiving the phase difference signal and generating an error signal for controlling an amount of power supplied to the motor as a function of the phase difference signal, the integrator having a negative summing junction;
• and
• a current injection circuit electrically connected to the negative summing junction, wherein the current injection circuit injects an offset current into the negative summing junction to cause about the maximum available voltage from a power source, coupled to the negative summing junction, to be supplied to the motor, coupled to the power factor control circuit, for a predetermined amount of time;
• wherein the current injection circuit comprises a programmable timer and a current injection resistor electrically connected to the programmable timer and to the negative summing junction, wherein the programmable timer supplies current through the current injection resistor for the predetermined amount of time, and
• wherein the current injection circuit is retriggered to cause full voltage to be supplied to the motor for a predetermined amount of time responsive to AC power being cycled off and on.

A power factor control circuit for an induction motor, comprising:

• a voltage/current phase difference generator for determining a difference in phase between a voltage applied to the motor and a current drawn by the motor, and for generating a phase difference signal as a function of the determined difference in phase, the voltage/current phase difference generator including an integrator, the integrator receiving the phase difference signal and generating an error signal for controlling an amount of power supplied to the motor as a function of the phase difference signal, the integrator having a negative summing junction;
• and a current injection circuit electrically connected to the negative summing junction, wherein the current injection circuit injects an offset current into the negative summing junction to cause about the maximum available voltage from a power source, coupled to the negative summing junction, to be supplied to the motor for a predetermined amount of time;
• current sensing resistor configured to sense the current through the motor, and wherein the current injection circuit comprises:
• an amplifier circuit configured to measure the voltage across the current sensing resistor and to convert the sensed current to an amplified voltage;
• a half-wave rectifier circuit electrically connected to an output of the amplifier circuit and configured to output a first value when the amplified voltage is of one polarity, and to output a second value when the amplified voltage is of another polarity;
• a comparator circuit electrically connected to an output of the positive half-wave rectifier circuit and configured to square an output waveform of the positive half-wave rectifier circuit responsive to the current though the motor exceeding the predetermined threshold current;
• and a programmable timer electrically connected to an output of the comparator circuit, the programmable timer including a current injection resistor between the programmable timer and the negative summing junction, and
• wherein the current injection circuit is triggered by current flowing through the motor, responsive to the current exceeding a predetermined threshold current.

A power factor control circuit for an induction motor, comprising:

• a voltage/current phase difference generator for determining a difference in phase between a voltage applied to the motor and a current drawn by the motor, and for generating a phase difference signal as a function of the determined difference in phase, the voltage/current phase difference generator including an integrator, the integrator receiving the phase difference signal and generating an error signal for controlling an amount of power supplied to the motor as a function of the phase difference signal, the integrator having a negative summing junction;
• and a current injection circuit electrically connected to the negative summing junction, wherein the current injection circuit injects an offset current into the negative summing junction to cause about the maximum available voltage from a power source, coupled to the negative summing junction, to be supplied to the motor for a predetermined amount of time;
• wherein the current injection circuit comprises:
• a half-wave rectifier circuit electrically connected across the power factor control circuit and configured to rectify an AC voltage across the power factor control circuit and to reduce the peak voltage to within the operating voltage range of the current injection circuit;
• a comparator circuit electrically connected to an output of the half-wave rectifier circuit and configured to square an output waveform of the half-wave rectifier circuit responsive to the voltage across the power factor control circuit exceeding the predetermined threshold voltage;
• and a programmable timer electrically connected to an output of the comparator circuit, the programmable timer including a current injection resistor between the programmable timer and the negative summing junction, and
• wherein the current injection circuit is triggered by current flowing through the motor, responsive to the current exceeding a predetermined threshold current.