A power thermistor (ST Series) is an NTC thermistor that is an inrush limiting thermistor which is used in high inrush switching power supply applications. Power thermistors are specially formulated to suppress high inrush currents in switching power supplies and other applications where the high initial starting currents are an issue. Power thermistors can handle high current and voltage levels. In an application with high initial voltage, the current flow is limited to an acceptable level due to the relatively high resistance of the device. Once the capacitors are charged, the power thermistor decreases in resistance to a level where the voltage drop is negligible. A Power thermistor has a black epoxy coated body with radial, tinned, solderable lead wires. Resistances range from 0.7 to 200 Ohms. Resistance tolerances are offered at 15%, 20%, 25% and 30%. The Maximum Steady State Current ranges from 0.1 to 30 amps.

Littelfuse acquired U.S. Sensor Corporation in 2017 and manufactures Power Thermistors