A thermistor, a semiconductor component renowned for its resistance value's acute sensitivity to temperature changes, falls into two distinct categories based on its temperature coefficient: the positive temperature coefficient (PTC) thermistor and the negative temperature coefficient (NTC) thermistor. The NTC thermistor, commonly used for temperature measurement, control, and compensation, is widely recognized as a temperature sensor. In contrast, the PTC thermistor not only measures and controls temperature but also doubles as a heating element and acts as a "switch". This multifunctional device combines the roles of a sensitive element, heater, and switch, aptly termed a "thermal switch".
The defining feature of an NTC thermistor is its negative temperature coefficient. This means that as temperature increases, its resistance significantly decreases. Leveraging this property, NTC components are frequently utilized in soft start mechanisms, as well as in automatic detection and control circuits, particularly in small household appliances. Conversely, a PTC thermistor is characterized by a corrected temperature coefficient, where its resistance notably increases with rising temperature, hence its common use in automatic control circuits.
The resistance value of a thermistor dynamically shifts in response to external temperature variations. Its textual symbol is denoted as "RT". Thermistors with negative temperature coefficients are marked as NTC, while those with positive temperature coefficients are indicated as PTC. The graphical symbol of the thermistor in circuits is represented using θ or t° to signify temperature. This juxtaposition of symbols and coefficients plays a crucial role in distinguishing between the NTC and PTC thermistors, guiding their appropriate application in various electronic circuits and devices.