PTC Thermistors - POSISTOR® The Murata PTC Thermistors - POSISTOR® - are Positive Temperature Coefficient (PTC) Thermistors. In a conventional NTC thermistor, the resistance decreases when the temperature increases, but the PTC Thermistors' resistance rises sharply when its temperature exceeds a specific temperature. These characteristics make Murata PTC POSISTORs ideal for circuit protection in a variety of applications such as temperature sensor and temperature compensation, and for current control in common household appliances, humidifiers, facsimile, copies, dryers of all kinds, refrigerators, freezers, and air conditioners.