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Thermistors are widely used in many fields. Thermistor products mainly include two series of resistance, respectively is negative temperature coefficient NTC thermistor and positive temperature coefficient PTC thermistor. Thermistor is mainly used for overheat protection, overcurrent protection, anti-surge, temperature detection, temperature control, temperature compensation, etc. It is widely used in military, medical, human life, industrial automation, automobile, security and fire protection, household appliances, communications and other fields and occasions requiring temperature measurement or overheat and overcurrent protection.
NTC thermistor is widely used in temperature sensing and control of household appliances, automobiles and industrial production equipment due to its high sensitivity, high reliability and low price. According to different uses, it can be divided into power type NTC thermistor, compensation type NTC thermistor and temperature measurement type NTC thermistor.
Switching power supply, motor, transformer and lighting power supply have a large surge current at the moment of switching on. This surge current can damage components (e.g., MOS tubes) or blow out fuses. This current can be effectively suppressed by connecting the NTC thermistor in series with the load. Thermistors have a large cold resistance that inhibits current until the power is switched on. Under a sufficiently large current load, its power consumption decreases as the resistance value drops to 1/(10 to 50) of its original value due to self-heating. Products using NTC thermistors should not be switched on and off frequently. When the product is shut off, the NTC thermistor must be fully restored from the state of high temperature and low resistance to the state of high resistance at room temperature to achieve the same surge suppression effect as last time.
Most quartz oscillators have a strong temperature dependence. In order to obtain good temperature characteristics, a constant temperature tank is usually used to keep the ambient temperature of the quartz oscillator constant. But that makes the equipment big and expensive. Nowadays, a temperature compensation circuit is often used in the quartz oscillator circuit, which can obtain good temperature characteristics in a relatively wide temperature range. This kind of quartz oscillator with temperature compensation circuit is called TCXO, and most of the temperature compensation components are chip NTC thermistors.
Under a certain measuring power, the resistance value of the NTC thermistor drops rapidly as the temperature rises. Using this feature, the corresponding temperature can be determined by measuring the resistance of the NTC thermistor resistor, so as to achieve the purpose of detecting and controlling the temperature.