Patent ID: 8217323

Claim:
A high-frequency heating apparatus for driving a magnetron, comprising: a DC power supply including an AC power supply, a rectifier circuit for rectifying a voltage of the AC power supply, and a smoothing capacitor for smoothing an output voltage of the rectifier circuit; a series circuit including two semiconductor switching devices, the series circuit being connected in parallel to the DC power supply; a resonance circuit having a primary winding of a leakage transformer and a capacitor, which are connected to each other, one end of the resonance circuit being connected to a middle point of the series circuit while the other end of the resonance circuit is connected to one end of the DC power supply; a drive unit for driving each of the semiconductor switching devices alternatively or drives the semiconductor switching devices so as to provide a period in which the semiconductor switching devices are turned off concurrently; a rectifier unit connected to a secondary winding of the leakage transformer; a magnetron connected to the rectifier unit; a dead time generation circuit that generates a dead time control signal for turning off the semiconductor switching devices concurrently; an error signal generation circuit generating an error signal based on a difference between an input current of the AC power supply and the reference current; and a frequency-modulated signal generation circuit that outputs to the dead time generation circuit a frequency-modulated signal obtained by controlling an amplitude of a rectified voltage signal output from the DC power supply based on the error signal, wherein the drive unit limits the lowest frequency of a frequency with which the semiconductor switching devices are driven, so that the lowest frequency is set to be high at the beginning of operation of the high frequency heating apparatus, and the lowest frequency is set to be lower gradually thereafter.