A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiter, temperature sensors (Negative Temperature Coefficient or NTC type typically), self-resetting overcurrent protectors, and self-regulating heating elements (Positive Temperature Coefficient or PTC type typically).
Thermistors are of two opposite fundamental types:
With NTC, resistance decreases as temperature rises to protect against inrush overvoltage conditions. Commonly installed parallel in a circuit. As current sink.
With PTC, resistance increases as temperature rises to protect against overcurrent conditions. Commonly installed series in a circuit. As resettable fuse.
HTC and PTC heating systems are often used in our heating pads series products for fast heating and overheating protection.