Difference between NTC thermistor and varistor.

Thermistors are divided into positive temperature coefficient thermistor PTC and negative temperature coefficient NTC. PTC is a current-limiting protection device, which has an operating temperature value ts. When the temperature in its body is lower than ts, its resistance value remains basically constant, and the resistance value at this time is called cold resistance. When the temperature of PTC resistor body is higher than ts, its resistance value increases rapidly. Because its resistance can increase rapidly with the increase of temperature, it is generally connected in series on the line to be used as overcurrent protection for transient large current. PTC has applications in both signal lines and power lines.

The series connection of NTC thermistors in AC circuits mainly serves as "current protection". In order to avoid the surge current generated in electronic circuits at the instant of startup, a power NTC thermistor is connected in series in the power supply circuit, which can effectively suppress the surge current at startup. After the suppression of surge current is completed, the resistance value of the power NTC thermistor will drop to a very small degree due to the continuous action of its current. It consumes negligible power and will not affect the normal working current. Therefore, using power NTC thermistor in the power circuit is the simplest and most effective measure to suppress the surge during startup and ensure the electronic equipment from being damaged.

Varistor is a noun of Chinese mainland, which means "the resistance value changes with the voltage within a certain current and voltage range", or a resistor with "the resistance value is sensitive to the voltage". The corresponding English name is "Voltage Dependent Resistor", which is abbreviated as VDR. The resistor material of piezoresistor is semiconductor, so it is a variety of semiconductor resistors. At present, the widely used "zinc oxide" (Zn0) varistor is composed of divalent element (Zn) and hexavalent element oxygen (O). Therefore, from the material point of view, zinc oxide varistor is a kind of "ⅱ-ⅵ I group oxide semiconductor". In Taiwan Province, China, piezoresistors are named after their uses, which are called "surge absorbers". Varistors are sometimes called "electric shock (surge) suppressors (absorbers)" according to their uses.

The varistor is a "safety valve" in the circuit. Its biggest feature is that when the voltage applied to it is lower than its threshold value "UN", the current flowing through it is extremely small, which is equivalent to a completely closed valve. When the voltage exceeds "UN", the current flowing through it increases, which is equivalent to the state of the valve being opened. Through the realization of this function, abnormal overvoltages can be suppressed and the circuit can be protected from overvoltage damage.