Patent ID: 6963477

Claim:
An overheat protection circuit comprising: a semiconductor switching element provided in a current path from a power supply to a load and performing operations of bringing the current path into conduction and interrupting the current path; and an operating-mode control circuit for controlling the semiconductor switching element in a first operating mode in which a conductive operation is shifted to an interrupt operation when the temperature of a temperature detection portion increases and reaches a predetermined interrupt temperature, and in a second operating mode in which the interrupt operation is shifted to the conductive operation 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; wherein the operating-mode control circuit includes a first positive-temperature-coefficient thermistor, a second positive-temperature-coefficient thermistor, and a control element, and using a change in resistance of the first positive-temperature-coefficient thermistor in the first operating mode and a change in resistance of the second positive-temperature-coefficient thermistor in the second operating mode, the operational shift of the semiconductor switching element is controlled by the control element, and each of the first and second operating modes is controlled in the state where both positive-temperature-coefficient thermistors are thermally coupled to the temperature detection portion.