What are PTC Thermistors?

PTC stands for "Positive Temperature Coefficient". PTC thermistors are resistors with a positive temperature coefficient, which means that the resistance increases with increasing temperature.

PTC thermistors are divided into two groups based on the materials used, their structure, and the manufacturing process. The first group of PTC thermistors is comprised of silistors, which use silicon as the semiconducting material. They are used as PTC temperature sensors for their linear characteristic.

The second group is the switching type PTC thermistor. The switching type PTC thermistor has a highly nonlinear resistance-temperature curve. When the switching type PTC thermistor is heated, the resistance starts to decrease at first, until a certain critical temperature is reached. As the temperature is further increased above that critical value, the resistance increases dramatically. This type of PTC thermistors is widely used in PTC heaters, sensors etc. Polymer PTC thermistors, made of a special plastic, are part of this second group and are often used as resettable fuses.