Abstract: A PWM DC motor control circuit having improved current sensing. A power switching device controls the DC motor in a common drain connection, whereby armature current sensing is achieved at the negative side of the power switching device. The control for the power switching device and the PWM control circuit are both referenced to the negative rail, and thus do not float or move up and down with the motor modulation. An RC combination is controllably and synchronously switched across the current sense resistor to produce a voltage Ve across the RC combination when the motor power switch is on. This RC combination provides an average voltage of Ve to the PWM control that provides a waveform that replicates very nearly the armature motor current. The DC motor control current has improved immunity to noise generated by the PWM control and other ambient noise.

Abstract: A compressor drive system that includes a thermostat producing a signal indicating the measured air temperature, a modulation control circuit connected to the thermostat to produce a motor drive signal from the temperature signal and which is output to a motor drive switching bridge circuit. The motor drive switching bridge circuit is connected to a rectifier that converts single phase alternating current to direct current. The switching bridge uses the motor drive signal from the modulation control circuit and the rectifier output to produce multiphase power including a speed control signal imposed on the power for regulating speed. A motor connected to drive a compressor is included. The motor is powered by the motor drive switching bridge circuit multiphase power output. The speed of the motor is controlled as a function of the temperature signal.

Abstract: An alarm system for signalling when a door of a refrigeration unit compartment is not fully closed comprises an alarm condition sensing system having a door sealing gasket magnet and a magnetically actuated switch. The gasket magnet produces an elongated narrow magnetic field for coupling the unit and the door in sealing relationship when the door is fully closed. The switch senses the magnetic field when the door is closed even though the magnet position may be anywhere in a band of possible positions. An alarm system signals when a door of a refrigeration unit compartment is not fully closed. The alarm assembly comprises a housing wall section, a vibratable alarm member, and mounting structure for connecting the alarm member to the housing wall section so that the housing wall section is driven by the number and vibrates relative to the housing when the member vibrates at an operating frequency. A plainly audible alarm is produced when a door ajar condition is sensed.

Abstract: A compressor drive system that includes a thermostat producing a signal indicating the measured air temperature, a modulation control circuit connected to the thermostat to produce a motor drive signal from the temperature signal and which is output to a motor drive switching bridge circuit. The motor drive switching bridge circuit is connected to a rectifier that converts single phase alternating current to direct current. The switching bridge uses the motor drive signal from the modulation control circuit and the rectifier output to produce multiphase power including a speed control signal imposed on the power for regulating speed. A motor connected to drive a compressor is included. The motor is powered by the motor drive switching bridge circuit multiphase power output. The speed of the motor is controlled as a function of the temperature signal.

Abstract: A temperature sensing circuit including a temperature sensing element located at a medium to sense the temperature of the medium. The sensing element is a resistive element with a range of resistive values corresponding to a range of sensed temperatures. The sensing element is connected to circuitry for detecting variations of the resistance of the element. The circuitry provides an output signal of one state when the element resistance increases beyond a first value and provides an output signal of a second state when the element resistance decreases beyond a second value.

Abstract: An air conditioner clutch control device includes a resistive type temperature sensor, connected to power dividers for providing a threshold voltage and a trigger voltage for first and second comparators. Resistor type power dividers provide first and second reference voltages to the comparators. Logic circuits are attached to the comparators for providing first and second state signals. Thus, when the temperature exceeds the first reference the first state is produced to turn on the air conditioner; when the temperature falls below the second reference, the second state is produced to turn off the air conditioner. A zener diode is provided to protect the logic circuits from transients in the battery source of power and from a reversal in polarity. A coil of a relay switch is operated by the first and second states to close a switch to energize a coil of a relay switch of an air conditioner's compressor.

Abstract: A temperature controller for an air conditioner including a temperature sensor that provides an output temperature from the air conditioning device, and a temperature rate of change comparison circuit for providing an indication signal that the rate of change from the temperature sensor exceeds a predetermined reference rate of change indicating that the rate of temperature change from the air conditioner is less than a reference cooling rate. The indication signal from the temperature rate of change comparison circuit is input to a disabling means that disables the air conditioning device. In an embodiment, the rate of change comparison circuit is connected to the thermostat for the system to sample the air conditioning temperatures for comparison with the reference cooling rate.

Abstract: A link regulator is disclosed for providing a regulated voltage over a wide range of input frequencies and load currents. The frequency of an internal VCO and the input frequency are phase compared to provide a reference error signal. The unregulated DC voltage is integrated for a duration proportional to the error signal. This duration controls a series switching element to provide a constant volts/seconds. The output of the series switching element is filtered to a DC voltage that controls the frequency of the VCO. The DC voltage is proportional to the error signal, thus providing a feed forward system to regulate the DC voltage. During the period when the series switching element is not conducting, a shunt switch presents a low impedance to the input of the filter to clamp the input to ground. This allows for operation over a wide range of load currents without losing regulation.

Abstract: A synchronized switching delay circuit including an oscillator and multivibrator for generating a synchronized delay pulse. The oscillator is divided into three waveforms shifted in phase by 120.degree.. A 4-16 decoder receives the three waveforms and the delay pulse outputs a series of blanking pulses that blank a portion of the leading edge of each of the pulses in each of the three waveforms and their complements to provide a leading edge delay. The resulting delayed waveforms are input to a three phase bridge circuit comprised of three pairs of complementary switches. The delay enables one of the switches in each pair to completely turn off before the other switch turns on.

Abstract: A missing pulse detector circuit is disclosed which includes a variable frequency VCO and a digital phase comparator. The phase comparator compares the phase of the VCO reference and the phase of a driving signal that drives a synchronous motor drive package. The output of the phase comparator is input to a loop filter to provide an error signal that controls the VCO frequency and phase. A second output on the phase comparator translates a phase difference into a pulse width. The pulse width is then input to an integrator circuit to delay the leading edge thereof. This delayed pulse is then input to a Schmidt trigger which provides a switching threshold. The output of the Schmidt trigger is utilized to inhibit the operation of a synchronous motor in the motor drive package. The missing pulse detector is operable to detect rapid increases in acceleration of the driving frequency and added or deleted pulses therein.