How refrigerator works

The microcomputer thermostat of the refrigerator consists of three parts: voltage transformation rectification, temperature detection and operation control.

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1. Microcomputer thermostat transformer rectification part of refrigerator

The mains 220v is stepped down to 9v via transformer b1, and d01-d04 forms a full-wave rectification circuit, which rectifies 9v AC from b1. C01-c04 is the filter capacitor, and then is regulated by the three-terminal regulator 7805. It is regulated to 5v output than 9v, and is supplied to the chip mc68hc05 (hereinafter referred to as icd) and the lm324 operator and its surrounding components. The rectified DC voltage is also used for three relays jl, j2, j3 and their associated control elements bg2 - bg4 and d06 - d08.

2. Microcomputer thermostat temperature detection part of refrigerator

The 5, 7, and 8 feet in the control circuit board slot cn2 are respectively connected with three signal components such as a freezer temperature sensing head, a refrigerating room temperature sensing head, and a defrosting temperature sensing head. The three thermistors are separately detected by the ij. The temperature of the refrigerator compartment and the evaporator, when the three temperatures change, the resistance of the thermistor changes. Accordingly, the level of the signal input pin of icl changes. The thermistor converts the temperature change of the refrigerator into a level signal and transmits this signal to the control element. R01-r04, c08 and c11 respectively filter high and low frequency clutter from the freezer and cold room to reduce interference and improve signal intensity. The 1-4 feet of cn2 are respectively connected with two variable resistors w2l and w22 to control the indoor temperature of the cold onion room and the freezer compartment. The signals of the two variable resistors are input to the 22-pin and 21-pin of the ICl as a comparison reference between the signals of the temperature sensing signal input pins 24 and 23 of the refrigerating compartment and the freezing compartment, thereby determining the opening and closing or the damper of the refrigerator. Open and close.

3. Microcomputer thermostat operation control part of the refrigerator; refrigerator operating state. It is completely controlled by icl, and its working principle is as follows.

The ambient temperature of the refrigerator is set to 32 ° C. The temperature is adjusted by the temperature fine-tuning control elements w21 and w22 respectively, and the temperature of the freezer humidity adjustment knob is "weak", "medium", "strong". When the freezer compartment temperature is set to -20 ° C ~ -18 ° C, -22 ° C ~ -20 ° C, -22 ° C ~ -24 ° C. When the temperature adjustment knob of the refrigerating compartment is correspondingly marked as "weak", "medium" or "strong", the temperature of the refrigerating compartment is set to 7 ° C to 9 ° C, 5 ° C to 7 ° C, and 3 ° C to 5 ° C. Icl uses this as a criterion to judge the signals transmitted from the two temperature sensing elements and determine the action.

When the temperature of the refrigerating compartment does not meet the requirements. If the refrigerating compartment damper is in the closed state at this time, icl turns on the relays j1 and j2 (after the jl is turned on, the damper motor starts to rotate, and when the damper is opened, the damper position switch is turned on, Send a signal to icl, after the chip receives the signal, close the door, the damper motor stops rotating, and complete the opening of the damper), so that the electric damper of the refrigerating compartment is opened, and the compressor and the freezer fan are in normal operation.

When the refrigerating temperature reaches the requirement and the freezing chamber does not meet the usage requirements, icl continues to turn on relay j2 and sends a signal to close the damper (the working principle is the same as opening the door). At this time, the compressor continues to operate and closes the air supply in the refrigerating chamber. throttle.

When the freezing compartment and the refrigerating compartment reach the operating temperature, the .icl is disconnected from j2, and the compressor is now stopped. There is no timer inside the sink 1, the freezer compartment temperature is lower than one 3 (the compressor running time, when the compressor running time reaches 12 hours, icl disconnects j2 to close the compressor. At the same time, it is turned on j3, cold The deciduous evaporator is heated and defrosted. The accumulator at the outlet of the evaporator is equipped with a thermistor. When the temperature of the sump reaches a certain value (about 6 ° C), the sink l is cut off according to the signal from the computing unit lm324. J3. Terminate the defrosting process.

Judging from the normal operation of the refrigeration system, the microcomputer icl is normal, and the resistance of the wli and r05-r07 is normal with the three-meter meter, and the 7-pin of the lm324 is not soldered to the circuit board. The signal of the input column 1 is not accurate. So sometimes it is not automatic. Boot up. Since the refrigerator was used in the kitchen for a long time, and the southern part was damp, the test machine was observed after re-welding. This failure did not occur again.