Abstract: A power controller for applying power to an induction motor or similar AC load has a variable drive circuit for staring and switching a portion of the AC input line power. In one mode, the input line power is fed straight through to the load. In another mode, the AC waveform is reshaped to improve the power factor or to boost its RMS value, e.g., for brownout protection. In a further mode the output power can be provided at a different frequency from the input line power. Vector control increases efficiency through power optimization, with sensing of load requirements. Sensing of regeneration pulses at the commencement of a half cycle can be employed for direct sensing of motor speed or load.

Abstract: PWM AC power is supplied to an induction motor or other AC load. The frequency and magnitude of the waveforms is controlled by detecting the peak voltage or width of the reverse EMF pulses at the commencement of the power waveform applied to the load, and then adjusting the applied AC power based on the detected peak voltage or width. Alternatively, the depth of width of a notch that follows the reverse EMF pulse can be detected and used to control the applied AC power.

Abstract: A supplemental circuit board is provided for a furnace and air conditioning system to power the blower motor so that there is normal heat speed during a heat cycle, and normal, full speed when there is a normal cooling cycle. When there is a call for economy, dehumidification, or partial speed cooling, an inverter provides pulsating power for efficient reduced blower speed operation. An actuator circuit provides a blower-motor in-use signal, and a low-speed logic circuit provides a low-speed signal when there is a call for reduced speed cooling. In case of circuit failure, the arrangement defaults to normal speed operation.

Abstract: An arrangement for driving a pair of actuator solenoids or coils of a gas valve having two or more solenoids employs a microprocessor or similar controller and an driver circuit. An output terminal of the microprocessor provides a steady low for OFF and a pulsating output signal for ON. A transistor switching device is gated by the microprocessor, drives the first solenoid as its collector load. A rectifying diode connects the first solenoid to an accumulator capacitor, which ramps up from flyback pulses that pass through the rectifier. A negative resistance discharge device conducts when the accumulated voltage exceeds a threshold to energize the second solenoid. In a favorable embodiment the impedance of the second solenoid is higher than the first solenoid. In a second embodiment, the actuator circuit for the second solenoid can be a voltage doubling flyback driven relaxation oscillator.

Abstract: A start circuit for a single-phase AC motor controls the current through the start or auxiliary winding based on time rate of change of voltage or current, or based on the current or voltage dropping or rising some fraction from inrush value, i.e., to 50% of initial start current or to 150% of initial start voltage. The circuit can also include a default timer to time out the start current after some preset period between 300 and 1000 milliseconds.

Abstract: A gas furnace control circuit combines an igniter circuit and a rectification flame detection circuit. Pulsating current is applied respectively to inducer and gas valve relay coils to actuate the furnace. A rectifier supplies flyback pulses from the inducer relay coil to a capacitor arrangement to accumulate flyback voltage. An ignition transformer has its secondary connected to the igniter and flame detection probe for generating an ignition arc. A hysteresis switch is coupled between the capacitor and the primary of the ignition transformer discharges current from through the primary whenever the stored flyback voltage reaches a predetermined threshold. Another capacitor is connected to the gas valve relay coil. A transistor has a signal impedance connected with its drain or power electrode to define an output terminal. A resistor network has a first resistor with one end connected to the capacitor and a its other end connected to the gate or control electrode of the transistor.

Abstract: Drive circuit for a blower motor employs a microprocessor control element, a controlled rectifier to provide DC power at a controlled rail voltage, and an inverter employing a pair of switching transistors arranged as a bridge inverter or half-bridge inverter. The drive circuit operates over a range of blower speeds and varies both the frequency and amplitude of bipolar pulses that are applied to the blower motor armature.

Abstract: An actuation circuit for an electromechanical relay employs a microprocessor and a switching transistor to actuate a relay over a wide range of applied voltages. The switching transistor is connected in series with the actuator coil. A voltage sensing circuit is connected to one input of the microprocessor, which produces a pulse-width modulated actuator output to gate the switching transistor. The microprocessor is suitably programmed so as to produce a pulse width modulated signal actuator signal whose duty cycle is a function of applied voltage. The RMS current through the relay coil is sufficient to ensure good actuation, but does not overstress the coil. The relay is selected to have its rated actuation voltage at or below a lower end of the expected range of applied voltages. A relay actuation boost arrangement can include a transistor or an SUS (silicon unidirectional switch) or similar negative resistance device.

Abstract: First-order failure mode arrangement for driving an actuator coil for a switch element employs a microprocessor controller and a driver circuit that includes an amplifier switching device, such as a transistor, a capacitor that ac-couples the output of the microprocessor to a control electrode of the amplifier switching device, and the actuator coil which is tied between a voltage source and an output electrode of the amplifier switching device. The microprocessor also has a capability of interrogating the on or off condition of the switch element. The switch element can be, for example, the gas valve relay for a gas furnace. The switch element can be tested to ensure that it is capable of both closing and opening when directed, and to ensure that of the switch element is not locked or frozen into a closed condition.

Abstract: An arrangement for driving actuator coils for two or more driven devices employs a microprocessor or similar controller and an actuator driver circuit. The actuator driver circuit controls two or more relay actuator coils from a single microprocessor output terminal. This output terminal can provide a high, low, or pulse output signal. An amplifier switching device, such as a transistor, whose base is coupled to the output terminal of the microprocessor, drives the first relay actuator coil as its load. A rectifying diode is connected to one end of a capacitor and thence through a negative resistance device to a second relay actuator coil or other driven device. The coil impedances are selected so that the second coil has a significantly higher impedance than the first coil. When output pulses appear at the microprocessor output terminal, the transistor switch pulses on and off, and thus energizes the first coil.

Abstract: Arrangement for interrogating multiple switch conditions employs a single input microprocessor for a plurality of switch elements that are coupled in series with an operating element and a power source. A variable oscillator has a control input and an output coupled to the microprocessor input, providing a periodic signal to the same. A plurality of impedance elements, e.g., resistors, each with a respective value, are coupled between a respective junction between two successive switch elements and the control input of said variable oscillator, such that the rate of said periodic signal varies as a function of the open or closed condition of the respective switch elements. For each switch being tested, the microprocessor looks for one predetermined frequency or pulse rate corresponding to an open condition and another corresponding to a closed condition.

Abstract: A hybrid or combination solid state/electromechanical relay circuit combines the advantageous features of solid state and electromechanical relays but avoids their disadvantageous features. An electromechanical relay includes a coil and a pair of contacts which close in response to energization of the relay coil; this pair of contacts being coupled between the load and the ac source. The relay coil is coupled through a switch to a source of dc coil voltage and is also connected to ground. A triac has its first and second main electrodes coupled in parallel to the pair of contacts of the electromechanical relay between the ac source and the load. A capacitor has one lead connected to the first lead of the relay coil and a second lead connected to the gate of the triac. On application of power to the coil, the capacitor charges through the triac, mining it on prior to the coil voltage of the relay reaching its design pick-up voltage. Then during switch dormancy, the coil-energized relay contacts carry the load.

Abstract: A start circuit for a single phase AC induction motor employs a triac or similar device in series with the motor start or auxiliary winding. The triac device has associated circuitry so that it turns on in response to an increase in the time rate of change of applied voltage. In one version a PNP transistor and a capacitive timing circuit are employed to cut in the start winding. In another version a second, pilot triac is employed.

Abstract: A three-phase power monitor operates a contactor between a supply of three phase electrical power and a three phase load. A phase integrity detector has three inputs connected respectively to the three phases of the electrical power. If a loss, reversal, or dissymmetry is detected, a photoemitting device is actuated. Actuation can also result from low or high line frequency. A power supply circuit is input with the three phases of power and has an output providing a dc level corresponding to the voltage level of the three-phase electrical power. A hold circuit has a first time constant associated with it and attains a hold level when current is applied to its input, but reverts to a release level after this current ceases. An interrogator circuit is coupled to the power supply and to the input of the hold circuit and provides a periodic recharge current to the hold circuit at a period that is shorter than the period of the hold circuit.

Abstract: A protective time delay delay circuit delays energization to an electric load until a predetermined time has elapsed from a previous deenergization. A transistor has its emitter connected to an ac conductor and has its base coupled to an RC timing circuit. The collector is connected to the gate of a triac whose current electrodes are coupled to the thermostat conductor and to a load device. A small resistor and a zener can be connected to the transistor to provide brownout protection. A temperature sensitive resistor can be included to increase or decrease the lockout period as a function of temperature. This resistor can be remotely mounted in thermal proximity to the load to be protected. A thermistor placed in parallel to latching capacitor can provide thermal overload protection.

Abstract: A start circuit for a single phase AC induction motor employs an impedance in series with the run winding to develop a voltage drop proportional to the current through the run winding, and a pair of LEDs or another light emitting device across this impedance to produce a light output whose intensity varies with the field current, and hence in a generally inverse relation with motor speed. A solid-state AC current switch, which can be a triac or a pair of back-to-back SCRs, is gated by a photosensitive circuit that includes a photosensitive element. A light conduit, which can be a light pipe or light dome, for example, carries the light output from the light emitting element to the photosensitive element. The device of this circuit is highly reliable, has no mechanical contacts, and is relatively insensitive to temperature and voltage fluctuation.