Patent ID: 8139963

Claim:
An image fixing apparatus comprising: a heater; a temperature detecting element which detects a temperature of said heater; a comparison circuit which compares an output of said temperature detecting element with a reference value; a relay which is provided in a power supply circuit for supplying electric power from a commercial power supply to said heater; a relay drive circuit which drives said relay; and an integration circuit which is provided in a signal path from said comparison circuit to said relay drive circuit and integrates a signal input to said integration circuit, wherein an integral value of the signal input to said integration circuit reaches a reference value, by which a level of a signal input to said relay drive circuit changes and said relay is switched to an open position; and a latch circuit having an input port connected to a signal path from said integration circuit to said relay drive circuit and an output port connected to a signal path from said comparison circuit to said integration circuit, wherein said latch circuit continuously transmits a signal from said output port to said integration circuit, upon a change in a signal level of said input port so that said relay is switched to the open position, and latches said relay in the open position.