Patent ID: 7358467

Claim:
An electric power supply apparatus for supplying electric power with different frequencies to an induction load to make the induction load work, comprising: a generator that outputs AC electric power with different frequencies; a matching circuit that constitutes, together with the induction load, a plurality of resonance circuits corresponding to the different frequencies; and a control circuit that controls the supply of the AC electric power output from the generator to one of the resonance circuits of the matching circuit so that the frequency of the AC electric power matches a predetermined resonance frequency, wherein the matching circuit comprises a transformer having a primary winding and a secondary winding, the primary winding being connected with the generator, the secondary winding and the induction load providing a plurality of series resonance circuits with an output frequency corresponding to different frequencies outputted by the generator, and the transformer converts a plurality of load resonance impedances to substantially equal oscillator output impedance.