Schematic diagram of thermistor temperature controller

Schematic diagram of thermistor temperature controller

Shown is a thermistor resistance temperature control circuit. Its core component is a bridge temperature detection circuit and a relay control circuit
. The thermistor is the core component and is also called a temperature sensing component. This circuit controls the relay by detecting the temperature inside the refrigerator, and
then controls the compressor through the relay, thereby achieving temperature control of the refrigerator.
    In this figure, the emitter and base of transistor VT1 are connected to one diagonal of the bridge, and the other diagonal of the bridge is connected to the 18V power supply.
RP is the refrigerator temperature adjustment potentiometer. When RP is fixed at a certain resistance value, if the bridge is balanced, the potential at point A is equal to the potential at point B.
The potential difference between the base and emitter of VT1 is zero, the transistor VT1 is cut off, the relay K is released, and the compressor stops running. As
the temperature inside the refrigerator gradually rises after shutdown, the resistance value of the thermistor R- continues to decrease, the bridge loses balance, the potential of point A gradually increases, and the base current lb of
transistor VT1 gradually increases. The collector current V also increases accordingly. The higher the temperature inside the box, the smaller the resistance value of Rr, the larger the hair, and
the larger the resistance. When the collector current increases to the pull-in current of the relay, relay K pulls in, turns on the power circuit of the compressor motor,
the compressor starts running, the system starts cooling operation, and the temperature inside the box gradually drops. As the temperature inside the box gradually decreases, the resistance value of the thermistor
R1 gradually increases. At this time, the base current of the transistor becomes smaller, and the collector current also becomes smaller. When the current is less than the release current of the relay,
the relay K releases , the compressor motor stops working due to power outage. After shutdown, the temperature inside the refrigerator gradually increases, and the resistance value of the thermistor Ri
continues to decrease, causing the circuit to perform the next working cycle, thereby realizing automatic control of the temperature within the refrigerator.