Thomas E Suita

US Patent:

57653828, Jun 16, 1998

Filed:

Aug 29, 1996

Appl. No.:

8/705489

Inventors:

William R. Manning - North Attleboro MA
Richard J. Lisauskas - Wrentham MA
Thomas E. Suita - Warwick RI
Thomas W. Sun - Los Angeles CA

Assignee:

Texas Instruments Incorporated - Dallas TX

International Classification:

F25B 4702

US Classification:

62154

Abstract:

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.