Refrigerator thermostat alternative circuit

When the thermostat of the refrigerator is damaged and it is difficult to configure a new thermostat for a while, the electronic thermostat introduced in this article can be used as an emergency replacement. 　　

working principle  　　

The circuit working principle of this device is shown in Figure 1. It uses a time base integrated circuit NE555 as a cycle timing controller. When the power is turned on, since pins ② and ⑥ of IC1 are low level, IC1 is triggered to set, and its pin ③ becomes high level. At this time, relay J is excited and closed, and its normally closed contact j1 is disconnected. , R5 does not work. At the same time, the normally open contact j2 is closed, and the refrigerator receives power and starts cooling. At this time, because the ③ pin of IC1 is in a high level state, the diode VD6 is turned on, and the current charges C1 through the resistors R1 and R2. As time goes by, when the voltage at both ends of C1 rises to 2/3 of the power supply voltage, IC1 automatically resets. , its ③ pin becomes low level, the corresponding relay J also loses power and is released, and the refrigerator stops working. After stopping working, because the ③ pin of IC1 is low level, j1 is connected to R5 at this time. Due to the connection of R5, the threshold voltage of IC1 is not 1/3 of the power supply voltage, but 1/2 of the voltage of IC1 ⑤ pin. At this time, C1 is discharged through R3, R4 and the internal discharge tube of IC1. When the voltage on C1 drops to about 1V, IC1 flips and sets again, that is, the ③ pin of IC1 turns to high level again. Therefore, due to the access of R5, the smaller resistance values ​​of R3 and R4 can obtain a longer delay, and at the same time, it can also reduce the difference in charging time between the first and subsequent times. According to the value of this schematic diagram, by appropriately adjusting R2 and R3, the startup and shutdown times of the refrigerator can be controlled to be about 5-15 minutes respectively. In order to extend the shutdown time of the refrigerator, the resistance of R5 can also be appropriately reduced. The component selection and production component list is shown in the table below. No. Name Model Quantity R1 Resistor 470K 1 R2 Trimmer resistor 1.5M 1 R3 Trimmer resistor 680K 1 R4 Resistor 360K 1 R5 Resistor 1.2K 1 C1 Electrolytic capacitor 470u/16V 1 C2 Polyester capacitor 0.04u 1 C3, C4 Electrolytic capacitor 220u/25V 2 VD1－VD6 Rectifier diode IN4001 6 IC1 Three-terminal voltage stabilizing IC LM7812 1 IC2 Time base circuit IC NE555 1 J Relay 15A 12V Such as: JCZ-22F 1 T Power transformer power ≥5W 1 When using, it should be appropriately adjusted according to the changes in different seasons. Adjust the resistance of R2 and R3 to ensure that the minimum and maximum temperatures of the refrigerator meet the required requirements. Generally, the difference between the maximum temperature and the minimum temperature in a refrigerator should be controlled between 6-10°C, the start-stop ratio per hour should not exceed 8, and the time of each shutdown should be adjusted to no less than 5 minutes. After the circuit is debugged, it can be installed in the plastic case, and the socket CZ can also be installed separately.