A thermistor is a type of resistor whose resistance depends on the temperature. The higher the temperature, the lower the resistance. We call the two fundamental types of thermistor’s PTC (Positive Temperature Coefficient), where resistance increases as temperature rises to protect against overcurrent conditions. Opposite of that, we have NTC (Negative Temperature Coefficient), where resistance decreases as temperature rises to protect against inrush overvoltage conditions.
Thermistor’s can be seen in an assortment of electronic applications, frequently in temperature sensors. These sensors can be seen in fire prevention and security equipment, automobiles, air conditioning units, copiers/printers, and a variety of kitchen appliances. Their field of use is limited where the temperatures do not exceed 200°C, but they are preferable to more expensive thermocouples and RTD’s because of their low cost and the simple electronic circuitry that’s required.