Thermistors

Thermistors

Thermistors are semiconductors whose resistance changes with temperature. Because of their dependence of resistance on temperature, these resistors can be used as temperature sensors. Out of all of the types of temperature sensors, thermistors are the most sensitive and nonlinear.

Thermistors are divided into two groups. The first type thermistors are called a positive temperature coefficient thermistor (PTC). In PTC thermistors, if the first-order temperature coefficient of resistance is positive, the resistance will increase when the temperature increases. In the second type of thermistors, called negative temperature coefficient (NTC) thermistors, resistance decreases as temperature increases. This occurs when the first-order temperature coefficient of resistance is negative.

Thermistors can be used in various applications. PTC thermistors can take the place of fuses in current-limiting devices for circuit protection, while NTC thermistors can be used as inrush-current limiting devices or as resistance thermometers. The temperature of battery packs and digital thermostats can be observed with either type of thermistors.