Thermostat substitute device for refrigerator

3020 ice blue

Photocoupler

The circuit operation principle of the device is shown in the figure. It uses a time base integrated circuit NE555 as a loop timing controller. When the power is turned on, since the pins 2 and 6 of IC1 are low level, the IC1 trigger is set, and the 3 pin becomes high level. At this time, the relay J is energized 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 starts to work and cool. At this time, since the 3 pin of IC1 is in a high state, the diode VD6 is turned on, and the current is charged to C1 through the resistors R1 and R2. When the voltage across C1 rises to 2/3 of the power supply voltage with time, IC1 is automatically reset. , the 3 feet become low level, the corresponding relay J is also discharged, and the refrigerator stops working. After stopping the operation, since IC1's pin 3 is low, j1 is connected to R5. Due to the R5 access, the threshold voltage of IC1 is not 1/3 of the power supply voltage, but 1/2 of the IC15 pin voltage. At this time, C1 is discharged through the internal discharge tubes of R3, R4 and IC1. When the voltage placed on C1 drops to about 1V, IC1 is re-turned again, that is, IC3's 3 feet turn high again. Therefore, since the R5 access can make the smaller R3 and R4 resistance values ​​obtain a longer delay, the first and subsequent charging time differences can also be reduced. According to the value of the schematic diagram, proper adjustment of R2 and R3 can change the startup and shutdown time of the refrigerator to about 5-15 minutes. In order to extend the shutdown time of the refrigerator, the resistance of R5 can be appropriately reduced.