Cold shutdown temperature control circuit using TWH9205

As shown in the figure, the circuit is composed of a zero-crossing switch control circuit composed of TW9205 and its peripheral components, a thyristor drive refrigeration control circuit and a sound circuit. The temperature sensor RT in the picture uses a thermistor with a negative temperature coefficient (NTC) and is connected to the inverting input terminal (pin 9) of the differential switching amplifier in the TWH9205 chip; and the positive input of the differential switching amplifier The terminal (pin 13) is connected to the potential clamping terminals 10 and 11, that is, pin 13 is clamped to a fixed potential. Adjust the RP1 value so that the output of TWH9205 is low level within the set temperature range and the thyristor VS is in a cut-off state. When the temperature of the thermistor RT rises to a predetermined value, the output state of the differential switching amplifier in the TWH9205 changes, and when the AC power supply crosses zero, the output terminal (pin 4) of the TWH9205 turns to high level, controllable Silicon VS is turned on, and the controlled electrical appliance is powered and put into operation (refrigeration). After a period of operation, the ambient temperature drops and the resistance of RT (NTC type) increases, causing the voltage at the inverting input terminal of the differential switching amplifier in the integrated circuit to also increase. When the voltage is higher than the clamping level of the non-inverting input terminal , turns to low level when the AC crosses zero, the thyristor VS is cut off, and the controlled electrical appliance is powered off and stops running. This cycle keeps the temperature of the controlled equipment or space within a certain temperature range. Because an NTC thermistor RT is added to the inverting input end of the differential switching amplifier, its temperature control method is "cold shutdown", which is commonly used for temperature control of air conditioners, refrigerators, and constant temperature hair dryers.