Temperature control circuit design and analysis

The working principle of the device application circuit is shown in Figure 2. It can be used in the water-on alarm system of the canteen steam flushing. θ is a positive temperature coefficient thermistor, which can be fixed on the iron bucket used for flushing water with epoxy resin. When the water temperature in the bucket is very low, the temperature of the iron bucket is naturally low, and the resistance of the PTC is also very small. The voltage divided by it and R makes the voltage at the ④ end of the controller DM lower than 1.6V, so the signal light H does not light up. Once the steam flushes the water and the water temperature gradually rises, the resistance of the PTC also increases immediately. When the water temperature reaches 100℃, the resistance of the PTC rises stepwise, making the voltage divided by the ④ end of DM greater than 1.6V. At this time, the signal light H lights up, indicating that the water is really on. PTC can be a positive temperature coefficient switching thermistor with a temperature Curie point of 100℃, such as the RZK2 series. The signal light H can be installed in the canteen duty room.