Fixing device usable with an image forming apparatus

An image forming apparatus comprising:

• a fixing roller to fix a toner on a recording medium;
• a heater to heat the fixing roller;
• an alternating current (AC) power source to supply an AC electric power to the heater;
• a first AC power supply line between the AC power source and the heater;
• a second AC power supply line between the AC power source and the heater;
• a thermistor to detect a temperature of the fixing roller;
• a power control switch disposed on the first AC power supply line to supply and interrupt the AC electric power from the AC power source to the heater;
• a switch controller to turn on/off the power control switch based on a temperature detected by the thermistor;
• a relay comprising:
• a first relay contact point disposed on the first AC power supply line between the AC power source and the power control switch;
• 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 heater and the power control switch;
• a direct current (DC) power supplier to supply a DC power to the relay coil;
• and
• a DC thermoswitch coupled to the relay coil 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 control switch 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 control switch,
• wherein an overheating by the heater is controlled without an AC thermoswitch connected in series on either the first AC power supply line or the second AC power supply line.