Patent ID: 8000619

Claim:
A fixing device usable with an image forming apparatus having a fixing roller to fix a toner on a recording medium, a heater to heat the fixing roller, and an alternating current (AC) power source to supply an AC electric power to the heater, the fixing device comprising: a power converting part to convert the AC electric power with a low frequency from the AC power source to a high frequency power suitable for induction heating of the heater and to apply the converted high frequency power to the heater; a relay comprising: a first relay contact point disposed on a first AC power supply line between the AC power source and the power converting part; and a relay coil to open and close the first relay contact point, the relay selectively supplying the AC electric power from the AC power source to the power converting part; a direct current (DC) power supplier to supply a DC power to the relay coil; and a DC thermoswitch interposed between the relay coil and the DC power supplier and mounted adjacent to the fixing roller so as to interrupt the DC power from the DC power supplier to the relay coil, when a temperature of the fixing roller exceeds a threshold temperature, causing the relay coil to open the first relay contact point, wherein the first relay contact point is situated with respect to the AC power source and the power converting part such that, when the first relay contact point is in an open position, the AC electric power from the AC power source is prevented from being supplied to the power converting part, thereby no high frequency power is applied to the heater, and wherein the DC thermoswitch comprises a plurality of DC thermoswitches connected in series such that, when at least one of the plurality of DC thermoswitches is switched to an open position according to overheating of the fixing roller, the DC power from the DC power supplier is prevented from being supplied to the relay coil to stop an operation of the power converting part and not to output the converted high frequency power to the heater.