Texas Instruments Corporation

William R Manning

Stanley J Nacewicz

Richard J Lisauskas

Jeffrey P Rudd

Mark C Carlos

Byron T Yarboro

Thomas W Sun

Thomas E Suita

An adaptive defrost control for a refrigerator is shown in which a single linear power supply (12) and microprocessor (U1) is used for both the adaptive defrost and cold control functions. According to a feature of the invention, a zero current crossing point switching scheme may be used to improve relay cycle life. According to another feature, a calibration procedure based on line frequency may be used to obtain multiples of a selected unit of time for any accumulated compressor run time and defrost heater energization times. According to another feature a sample and hold technique may be used to distinguish between noise and valid signals. In a modified embodiment, a toroid (40) has a primary connected to a common line leading to the compressor motor (24) and defrost heater (26) to provide a signal (ST) which, when taken with the state of relay contacts in respective lines energizing the compressor motor and defrost heater, as determined by the microprocessor, results in monitoring the compressor and defrost heater energization time. In another embodiment, a motor start control incorporating a PTC element (28) is combined with the adaptive defrost control. A double pole, single throw relay (K4) initiates both the compressor motor starting and refrigerator heater functions and open circuits the PTC element after starting has been completed in order to conserve power. In a modified embodiment the latter relay (K4) is used to start the compressor motor without the PTC element (28).

Adaptive defrost system

An electronic motor protection system is shown having a power supply usable with multivoltage supplies and providing protection from over-temperature conditions caused by various fault conditions. The system also has optional features of a time delay for re-energization and for low voltage protection. The system is mounted on a circuit board and encased in potting material which also locks the two housing parts together. A miswiring feature is also provided to prevent connecting line voltage to the control circuit or sensor terminals.

Electronic motor protection apparatus

A phase monitor and protection circuit is shown in which an impedance network (21, 23, 25) in a respective branch (20, 22, 24) connected to a neutral (26) is coupled to each phase of a three phase power supply (L1, L2, L3) to create a known voltage profile across the respective networks. A relay network (36) is coupled to one branch (20) and a control network (30) is coupled to a second branch (24) to monitor the voltage levels and deenergize the relay (R1) upon the occurrence of the reversal of any two phases or the loss of a phase. The control circuit can also be used to detect low voltage conditions and in a second embodiment provides a time delay network (44) to avoid nuisance tripping due to transient low voltage or brown out condition.

Phase monitor and protection apparatus

A phase sequence protection circuit is shown in which first and second resistors (R1, R2) and a first capacitor (C1) all having equivalent impedance are connected in a Y configuration and coupled to power source leads (A, C, B) of a three phase power supply, resistor R1 being coupled to phase A, capacitor C1 to phase B and resistor R2 to phase C. A comparator network (12) is connected in line with the first resistor (R1) and, in one embodiment will cause a solid state switch (Q1) to conduct when the phases are out of sequence. In a second embodiment a buffer portion (COMP2) is provided to add switching hysteresis which also reverses the switching logic causing the solid state switch (Q1) to conduct when the phases are in sequence. In another embodiment the comparator network (12') is provided with the buffer portion (COMP2) for switching hysteresis and arranged to cause the solid state switch (Q1) to conduct when the phases are out of sequence. An opto-isolator (14) interfaces with the comparator network (12, 12', 12') to provide isolation. The signal from the opto-isolator in comparator network (12') controls the energization of a second solid state switch (Q2) and a relay coil (K1) used to energize a load.

Phase sequence wiring protection apparatus

A electronic motor protection system is shown having a power supply (12) usable with multivoltage supplies and providing protection from over-temperature conditions caused by various fault conditions. The system also has optional features of a time delay (20) for re-energization and for low voltage protection (22). The system is mounted on a circuit board and encased in potting material which also locks two housing parts together (30, 34). A miswiring feature is also provided to prevent connecting line voltage to the control circuit or sensor terminals.

An autotransformer is used to replace the start capacitor in a split phase induction motor. The autotransformer windings are protected by a PTC resistor which also serves to effectively de-energize the auxiliary winding. In a preferred embodiment, efficiency of the motor in the run mode is enhanced by shunting the secondary of the autotransformer with an NTC element. In alternative embodiments a relay coil is placed in series with the auxiliary winding circuit to remove the PTC and the primary of the autotransformer from the circuit when the motor is in the run mode.

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Wrentham, MA, United States of America

William R Manning