The temperature controller introduced in this example has the characteristics of convenient materials and reliable performance. It can be used for temperature control of seed germination, edible fungus cultivation, young animal breeding and egg egg formation, etc. It can also be used to control electric blankets, low-power electric Household appliances such as heaters.

Working principle

After 220V AC voltage is reduced by C1 and R1, VD1 and VD2 rectified, C2 filtered and VZ stabilized, one is used as the input DC voltage of IC (TL431 three-terminal stabilized integrated circuit); the other is divided by RT, R3 and RP After pressing, provide control voltage for IC.

When the measured temperature is lower than the set temperature of RP, the resistance value of the NTC502 negative temperature coefficient thermistor RT is larger, and the control voltage of the IC is higher than its turn-on voltage. The IC turns on to make the LED light up and VS is When triggered and turned on, the electric heater EH is energized to start heating.

As the temperature continues to rise, the resistance value of RT gradually decreases, and the control voltage of the IC also decreases. When the measured temperature is higher than the set temperature, the IC cuts off, the LED is extinguished, the VS is cut off, and the EH loses power and stops heating. Then the temperature began to drop slowly. When the measured temperature was lower than the set temperature, the IC turned on again, and the EH began to be electrically heated. This cycle continues, and the measured temperature is controlled within the set range.