Fusing device for instantly controlling power

An image forming apparatus comprising :

• a fusing device to fuse and fixe a toner onto a print paper, wherein the fusing device comprises:
• an AC current generating unit which generates an AC current having a frequency corresponding to a pulse width modulation signal;
• a transformer which receives the AC current and generates a magnetically induced current corresponding to the AC current;
• a fusing unit which is resistance heated or induction heated by the induced current, and fuses the toner onto the print paper using the generated heat;
• a sensing unit which senses the temperature of the fusing unit;
• a reference current generating unit which compares the temperature of the fusing unit sensed by the sensing unit with a predetermined reference temperature of the fusing unit, and generates a predetermined reference current for controlling the temperature of the fusing unit based on the result of the comparison between the temperatures;
• and
• a pulse width modulation signal generating unit which compares the reference current with the induced current input to the fusing unit, generates the pulse width modulation signal so that the induced current can be close to a value of the reference current, outputs the pulse width modulation signal to the AC current generating unit, and controls a frequency of the pulse width modulation signal so that a value of the induced current gradually increases to the value of reference current during a predetermined amount of time so as to prevent the value of the induced current from dramatically increasing.