Electrical appliances such as refrigerators and air conditioners require a cold temperature control shutdown circuit to complete the automatic control. The main function of these devices is to cool down, and when the temperature drops to a certain value, it should be stopped.
As shown, RL is the cooling load and K is the power switch. BCR is an electronic switch and Rntc is a negative temperature coefficient Thermistor. 555 is used as a level comparator to drive the BCR to complete the power on/off switching of the load RL. A 50KΩ potentiometer is used to adjust the set low temperature point.
When the temperature of Rntc is higher than the set point, its resistance is smaller, which will make the 555 second foot higher. Then 555 3rd and 7th feet are low level, and BCR turns on RL to work. When the temperature reaches the set point, the 3rd and 7th feet of 555 are high level, and the BCR is cut off to stop the RL from being powered off.
Bi Directions Thyristor (Triac)
Bi Directions Thyristor (Triac) is equivalent to the antiparallel connection of two unidirectional thyristors, but only one control pole.
Bidirectional thyristors are made of N-P-N-P-N five-layer semiconductor materials, and three electrodes are also derived from the outside. Its structure is shown in the figure. Bi-directional thyristor volt-ampere characteristic curve Since the forward and reverse characteristics of the bidirectional thyristor are symmetrical, it can be turned on in any direction and is an ideal AC switching device.
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