Patent claim: A power control apparatus for highfrequency dielectric heating for controlling an inverter power supply circuit which includes a DC power supply circuit configured to generate a DC power source produced by rectifying a voltage of an AC power source at least one or more of a series circuit which has at least two semiconductor switching devices and to which the DC power source is input a resonance circuit which is connected to the series circuit and includes a primary winding of a leakage transformer and a condenser the primary winding and the condenser being seriesconnected and a rectifier circuit connected to a secondary winding of the leakage transformer and configured to supply high voltage to a magnetron and the power control apparatus comprising a control circuit which comprises an input current detection section configured to detect an input current of the AC power source and to output input current information an input voltage detection section configured to detect an input voltage of the AC power source and to output power supply voltage waveform information a resonance voltage comparison section configured to output resonance voltage control information based on a resonance circuit voltage information taken from the leakage transformer an input current comparison section configured to outputpower control information based on the input current information a magnetron oscillation detection section configured to determine when a predetermined time has elapsed after the input current information is compared with a threshold value of the magnetron oscillation comparison information and the input current information exceeds the threshold value of the magnetron oscillation comparison information that the magnetron is oscillating stably and set the magnetron oscillation detection information to be true a mixing circuit configured to generate a switching frequency control information from the power supply voltage waveform information based on the resonance voltage control information or the power control information selected depending on the magnetron oscillation detection information a minimum frequency limiting circuit configured to select a predetermined minimum frequency depending on the magnetron oscillation detection information so as to limit a minimum frequency of the switching frequency control information having been output from the mixing circuit and a switching pulse generation section configured to generate drive signals each for driving each of the semiconductor switching devices based on the switching frequency control information from the minimum frequency limiting circuit and output each of the drive signals to each of the semiconductor switching devices.

Related passage: There is a configuration of the oscillation detector 248 using the characteristic that a clear difference occurs between before and after the oscillation start of the magnetron while the resonance voltage of the resonance circuit is maintained at a given level and making a comparison between the preset oscillation detection threshold level between lin1 and lin2 as shown in FIG.28 and the output of an input current detection section by a comparator etc.and latching the output or the like.