Understand the structure and working principle of thermistor in three minutes

　　During normal operation, the current flowing through the thermistor is less than its rated current, and the resistance value is small and the power is small, which does not affect the normal operation of the circuit; the moment of startup, lightning strike or static electricity, etc., will generate a very large surge current, the current flowing through It will suddenly exceed its rated current, the PTC will heat up, and the resistance value will show a high impedance instantaneously, which inhibits the current from flowing to the subsequent circuit and acts as a current limiter. After the current returns to normal, the impedance decreases, and the PTC returns to a low-impedance state.

　　It can be seen that this thermistor can be used in all household appliance circuits to play the role of overcurrent and overload protection. At this stage, the cost pressure of electronic products is very high. We dismantled some electrical appliances and found that some manufacturers have canceled this thermistor. When there is a surge current, if there is no such resistance, some capacitors and switches on the circuit may explode. The fire caused a huge safety hazard. Safety is no trivial matter, canceling this thermistor should not be done.

　　There is also a type of thermistor whose resistance value decreases as the temperature increases, which we call a negative temperature coefficient thermistor (NTC).

　　Different from the role of PTC as a protection device, in household appliances, we usually use the characteristics of NTC as a temperature sensor, such as washing machine detection of water temperature, dryer drum temperature detection, etc., its appearance and internal structure

　　In the application of the above scenario, a cylindrical packaged NTC thermistor is usually used. The actual application circuit is as shown in the figure below. The NTC temperature sensor is connected in series with the 5-pin and 6-pin, and a voltage divider is connected in series between the 5-pin and 5V voltage. When the change occurs, the voltage value received by the single-chip microcomputer changes differently. According to the RT curve of the thermistor (corresponding curve of resistance temperature), the temperature at the location of the thermistor can be obtained, so as to control other loads (heating pipe, drainage pump, compression machine, etc.) working status.

　　When designing the actual circuit of household appliances, we mainly focus on the temperature range, accuracy, precision, rated voltage and current of the thermistor.

　　The above is an introduction to thermistors, is it very simple? Welcome to leave a message in the comment area.

　　In the follow-up, we will introduce the electrical devices used in household appliances one by one, and slowly describe how a product reaches consumers. I believe that you in front of the mobile phone will definitely be very interested.

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