A thermistor is a temperature-sensitive resistor, which is generally made of semiconductor materials, and its resistance also changes when the temperature changes.
(1) Appearance of thermistor (2) Type of thermistor
There are many types of thermistors, which can usually be divided into positive temperature coefficient thermistors (PTC) and negative temperature coefficient thermistors (NTC).
① Negative temperature coefficient thermistor, referred to as NTC, its resistance decreases with the increase of temperature. NTC is made of metal oxides such as manganese oxide, cobalt oxide, nickel oxide, copper oxide and aluminum oxide as the main raw materials. According to different operating temperature conditions, NTC thermistors can be divided into three types: low temperature (-60～300℃), medium temperature (300～600℃) and high temperature (>600 degree ). According to the function, it is divided into four types: power type, compensation type, temperature measurement type and temperature sensor.
Every time the temperature of the NTC increases by 1 degree , the resistance value will decrease by 2 percent to 6 percent , and the degree of resistance decrease depends on different models. NTC is widely used in temperature compensation and temperature automatic control circuits, such as refrigerators, air conditioners, greenhouses and other temperature control systems often use NTC as temperature measurement components.
② Positive temperature coefficient thermistor is referred to as PTC, and its resistance value increases with the increase of temperature. PTC is made of barium titanate (BaTiO2) doped with an appropriate amount of rare earth elements.
PTC can be divided into slow type and switching type. The resistance of the slow{{0}}type PTC increases by 0.5 percent to 8 percent for every 1 degree increase in temperature. The switching PTC has a turning point temperature (also known as the Curie point temperature, the Curie point temperature of the barium titanate material PTC is generally about 120 degree ), when the temperature is lower than the Curie point temperature, the resistance value is small, and the temperature changes When the resistance value is basically unchanged (equivalent to a closed switch), once the temperature exceeds the Curie point temperature, the resistance value will increase sharply (equivalent to the switch being turned off).
Slow-type PTC is commonly used in temperature compensation circuits. Switch-type PTC is often used in circuits that are turned on at the moment of startup and then disconnected immediately, such as degaussing circuits of color TVs, compressor startup circuits of refrigerators, and overcurrent and overheating protection. The circuit uses switching PTC.
