Overheat protection circuit

摘要

A semiconductor switching element performs operations of bringing a current path from a power supply to a load into conduction and interrupting the path and is controlled by an operating-mode control circuit so as to operate in a first operating mode in which a conductive operation is shifted to an interrupt operation by using a change in resistance of a first positive-temperature-coefficient thermistor when the temperature of a temperature detection portion increases and reaches a predetermined interrupt temperature, and to be in a second operating mode in which the interrupt operation is shifted to the conductive operation by using a change in resistance of a second positive-temperature-coefficient thermistor when the temperature of the temperature detection portion decreases and reaches a return temperature, which is lower than the interrupt temperature by a predetermined value. Each operating mode is controlled in the state where both positive-temperature-coefficient thermistors are thermally coupled to the temperature detection portion.