Patent GB-1475131-A (GB)
Title: Refrigerator control apparatus
IPC: F25B49/02
Filed: 1974-06-18
Abstract: 1475131 Refrigerator control systems HITACHI Ltd 18 June 1974 [20 June 1973 31 Aug 1973 5 Nov 1973] 27001/74 Heading H2H A refrigerator control apparatus for controlling at least one device in a refrigerator by a plurality of control timing signals comprises an electronic timer including at least one counter which includes a plurality of flip-flop circuits connected in multiple stages succeedingly from a first stage thereof to which clock pulses are applied for counting the clock pulses together with means for taking outputs from the different stages of the timer and means responsive to the outputs of the different stages to produce the respective control timing signals. A control system for a refrigerator comprises a compressor 2 energized from an A.C. source 3 by way of a triac 4, the gating signal for which is derived by an AND circuit 6, a circuit 5 being provided to detect any overloading of the compressor motor. A thermistor 16 located in the refrigerator detects the refrigerator temperature, the resulting signal being amplified by an amplifier 17 and fed to a flip-flop 19. The Q output of the flip-flop 19 changes between 1 and 0 as determined by the thermistor 16 and is fed to the terminal 1 to start and stop the compressor 2. Differentiating circuits 20, 21 and a counter circuit 22 are provided to ensure that a predetermined time-say 5 minutes-elapses after the compressor 2 stops before it can be restarted. An overload control arrangement for the compressor 2 comprises a timing device 10 which comprises a number of R-S flip-flop circuits C 1 -C 14  in cascade, which circuits have a power supply 11 and are driven by a clock pulse generating circuit 12. Outputs 0 and 1 are taken at regular intervals from the timing devices 10 at terminals O 8 , O 14  of circuits C 8 , C 14  which represent timings of, say 2¢ and 160 seconds respectively. The output O 8  is fed to an AND circuit 7 and output O 14  to a flip-flop 14. If the circuit 5 detects an overload, a signal is applied to the AND circuit 7 and after 2¢ seconds the AND circuit 7 receives a further signal from the output O 8 . Thus if the overload persists for longer than 2¢ seconds an output is derived from the AND circuit 7 which causes the flipflop 9 to block the AND circuit 6 to stop the compressor 2. Before the compressor can be restarted the output O 14  must produce a signal after-say 160 seconds-which resets the flipflop 9 to open the AND circuit 6 so allowing the compressor 2 to be re-energized. The control system also includes a defrosting system which includes a defrosting heater 30 energized from an A.C. source 31 by way of a triac 32, the gating signal for which are produced by a binary counter 33 having flip-flops C 1 -C 33  in cascade having a power supply 34 and driven by a clock pulse generating circuit 36. After a time of-say 22 hours-an output O 23  appears to gate the triac 32 thereby energizing the heater 30 to defrost the refrigerator. After a further time of-say 42 minutes-an output O 18  appears which resets the flip-flop C 23  to terminate the defrosting operation, the cycle repeating when an output O 23  next appears. Fig. 7 shows the system including the compressor, the overload protection and the defrosting control circuits, the binary counters 10 and 33 being combined. If desired the system may include a fan and its associated control circuit.