Patent ID: 8036557

Claim:
A fixing device comprising: a permeable member having a predetermined thickness; an induction heating member configured to excite the permeable member to generate an eddy current in the permeable member; a current supply circuit configured to supply an AC current to the induction heating member; and a control unit, when temperatures of a first portion and a second portion of the permeable member are a first temperature lower than a temperature T TH conforming to the following formula: d = 2 ⁢ ρ ω 1 ⁢ μ ( T TH ) where d: a thickness [m] of the permeable member, ρ: a resistivity [Ω·m] of the permeable member, (ω 1 ): an angular frequency [rad/s] of a first drive frequency, and μ: a permeability [H/m] of the permeable member, configured to control so as to permit the current supply circuit to supply the AC current at the first drive frequency to the induction heating member, and when the temperature of the second portion of the permeable member excited at the first drive frequency is a second temperature higher than the temperature T TH , to control so as to permit the current supply circuit to supply the AC current which conforms to the following formula: d < 2 ⁢ ρ ω 2 ⁢ μ ( T 2 ) where ω 2 : an angular frequency [rad/s] of a second drive frequency and flows at the second drive frequency higher than the first drive frequency to the induction heating member.