A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word is a combination of thermal and resistor. Thermistors can be classified into two types: positive temperature coefficient (PTC) thermistors and negative temperature coefficient (NTC) thermistors.
PTC thermistors can be used as heating elements in small temperature-controlled ovens. NTC thermistors can be used as inrush current limiting devices in power supply circuits. Inrush current refers to the maximum, instantaneous input current drawn by an electrical device when first turned on. Thermistors are available in a variety of sizes and shapes; the smallest in size are the beads with a diameter of 0.15mm to 1.25mm.