RTI Electronics' solid state over-temperature protectors are designed to sense the temperature of power transistors, heat sinks, chassis, etc. Construction consists of a small 0.2" diameter positive temperature coefficient thermistor disc attached to an anodized aluminum mounting tab using thermally conductive epoxy.

The devices remain in their low resistance state at all temperatures below the switch temperature. When the switch temperature is reached or exceeded, they increase in resistance rapidly thereby limiting current to the drive circuitry to protect the critical components. Once the temperature decreases to a normal operating level, the device resets to its low resistance state.