| 摘要 |
An induction heating apparatus is provided with a control circuit 5 which comprises a resonance waveform detector 6 for detecting a high frequency AC waveform supplied from an inverter circuit 3 to a heating coil 4 to produce a detection signal DS<SUB>1 </SUB>corresponding to high frequency AC power waveform; a phase comparator 8 for producing an adjusting signal PH corresponding to a phase difference between detection signal DS<SUB>1 </SUB>from resonance waveform detector 6 and drive signal D<SUB>1 </SUB>from drive circuit 7; and an addition circuit 13 for superimposing the drive signal D<SUB>1 </SUB>from drive circuit 7 on detection signal DS<SUB>1 </SUB>from resonance waveform detector 6 to supply the superimposed signal to phase comparator 8 . Even though power source 60 generates the output of lowered voltage level, at least a part of the superimposed signal of detection signal DS<SUB>1 </SUB>and drive signal D<SUB>1 </SUB>can be maintained on a level same as or over operation threshold value V<SUB>TH </SUB>for phase comparator 8 , while keeping normal operation of phase comparator 8 . Thus, in detecting resonance current flowing through inverter circuit 3 in the apparatus to control oscillation frequency of drive signals to IGBTs 11 and 12 , the induction heating apparatus can always stably turn IGBTs 11 and 12 of inverter circuit 3 on and off even with lowered resonance current through inverter circuit 3.
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