| 摘要 |
PROBLEM TO BE SOLVED: To provide an output of a microwave generating means even where a supply voltage is low with the phase of an AC power supply in the vicinity of 0 deg. and 180 deg.. SOLUTION: A frequency conversion circuit 2 is connected to an AC power supply 1. The frequency conversion circuit 2 comprises a DC power supply circuit 4 which converts the AC power supply 1 to a DC power supply, and a grade quasi-E inverter circuit 13 connected to the output side of the DC power supply circuit 4. The inverter circuit 13 has a resonance circuit 10, an IGBT (insulated gate bipolar transistor) 11, and a freewheel diode 12 connected in inverse parallel with the IGBT 11. A resonance voltage detecting circuit 50 detects the resonance voltage of the supply resonance circuit 10 and a control circuit 19 controls the on-period of the IGBT 11 so that the lower the detected voltage is detected by the resonance voltage detecting circuit 50, the longer the on-period is controlled.
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