| 摘要 |
PURPOSE:To miniaturize a secondary circuit including a magnetron by preventing an overvoltage from being outputted from a secondary winding even when the magnetron is not yet started CONSTITUTION:A half bridge converter, containing switching elements 20a and 20b and a high frequency transformer 34, is driven by a 200V commercial power supply 14. A control circuit 12 generates a first and a second switching signal, comparing the voltage equivalent to the average value of a current detected by a current transformer 44 with a standard voltage, at the frequency proportional to the differential voltage therebetween. Switching elements 20a and 20b are alternately turned on, the resulting high frequency high voltage, induced across a secondary winding 34b, is applied in a magnetron 36 via a voltage doubler rectifier circuit. When the voltage of a commercial power supply exceeds a predetermined value in the state such that the magnetron 36 is not yet started, the first switching signal is provided in a switching element 20a by a gate 61 and being inhibited, so that the oscillation operation of the half bridge converter is stopped.
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