| 摘要 |
PROBLEM TO BE SOLVED: To control heating power in a wide range while synchronizing on- timing of a switching means with respect to zero-cross timing. SOLUTION: To coils 151 and 152 in inductances L1 and L2, capacitors 211 and 212 for resonance in capacitances C1 and C2 are respectively connected in parallel, for constituting LC resonance circuits 221 and 222. A change-over switch 23 connects either of the LC resonance circuits 221 and 222 to a semiconductor switching element 24. A control part 25 controls connection conditions by the change-over switch 23 to maintain the surface temperature of a heating roller at an operating temperature. For increasing heating power, the change- over switch 23 is switched to the LC resonance circuit 221, and for setting heating power low, the change-over switch 23 is switched to the LC resonance circuit 222.
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