Thermistor

A thermistor is a passive electronic component whose resistance varies significantly with temperature. Most thermistors are made from ceramic metal oxide powders sintered into beads, disks, or chips, though polymer-based thermistors are also used. They are inexpensive, compact, and offer high sensitivity to temperature changes.

Thermistors are broadly categorized into two main types: negative temperature coefficient (NTC) and positive temperature coefficient (PTC). NTC thermistors have resistance that decreases as temperature increases and are widely used for temperature sensing, measurement, and inrush current limiting in power products. PTC thermistors have resistance that increases with temperature and are commonly used as resettable fuses and for overcurrent protection, as well as in some temperature-compensation applications.

Electrical behavior varies by type. In NTC devices, increasing temperature increases charge carriers, lowering resistance. In PTC devices, higher temperatures lead to an increase in resistance due to material-specific mechanisms such as grain-boundary effects or changes in conductive pathways in polymer composites.

Thermistors come in various form factors, including beads, disks, and chips for ceramic types, and film or polymer formats for polymer-based devices. Materials range from metal oxides used in ceramic thermistors to conducting polymers embedded in a matrix for polymer PTCs. This diversity allows tailoring of sensitivity, response time, and temperature range for specific applications.

Applications span temperature sensing in household appliances, automotive and industrial systems, medical devices, and consumer electronics, as well as inrush current limiting and resettable fuses in power supplies. Key considerations when selecting a thermistor include its resistance-temperature characteristic, accuracy, stability, response time, and operating temperature range.