Patent ID: 7856190

Claim:
A heating device that heats, by electromagnetic induction heating, a heating member disposed in a fixing device for use in an image forming apparatus, which fixing device heats and fixes an image on a recording material while nipping and transporting the recording material, the heating device comprising: an exciting coil that is disposed along the heating member and generates an alternating magnetic flux to heat the heating member by the electromagnetic induction heating; a demagnetizing coil that encircles part of the alternating magnetic flux generated by the exciting coil and generates an electro motive force in a direction that cancels the alternating magnetic flux; a switching member for forming a closed circuit in which a demagnetizing current generated by the electro motive force of the demagnetizing coil flows; and a demagnetizing current regulator provided in the closed circuit in which the demagnetizing current flows for adjusting the demagnetizing current, wherein the demagnetizing regulator includes a capacitor for causing LC resonance between the demagnetizing coil and the capacitor so that the demagnetizing current is increased due to the LC resonance between the demagnetizing coil and the capacitor, wherein the heating device is configured to detect a drive frequency of the exciting coil, and when the detected drive frequency changes, a resonance frequency of the LC resonance between the demagnetizing coil and the capacitor is changed by changing a capacity of the capacitor, wherein a range of variation of the resonance frequency of the LC resonance between the demagnetizing coil and the capacitor does not overlap a frequency of an exciting circuit so that the range of variation of the resonance frequency is higher or lower than a resonance frequency of the exciting coil.