Load applicability detecting device for induction-heating cooking apparatus

Claim 1

A load applicability detecting device for an induction-heating cooking apparatus, comprising: (a) a heating coil for heating metallic cooking pans by means of electromagnetic induction; (b) an inverter comprising a switching element connected in series with said heating coil, said inverter causing a high frequency current to flow through said heating coil when the switching element is turned on and off; (c) soft starting means for gradually decreasing an output frequency of said inverter from a predetermined large value to a predetermined small value for a predetermined short period of time by controlling an on-off cycle of the switching element so that an inverter input current is caused to gradually rise for the period of the starting of said inverter; (d) input current detecting means connected to the AC input side of said inverter for detecting the inverter input current at an initial stage of the starting of said inverter, thereby obtaining a detection signal, the level of which is in accordance with that of the inverter input current; (e) a power source switch operated prior to the starting of said inverter for supplying a switching element control circuit with a control power source; (f) a first integrating circuit starting an integrating operation when said power source switch is operated, said first integrating circuit generating a first timing signal when an integrated output thereof reaches a first level; (g) control means for supplying said inverter with a starting signal so that the on-off operation of the switching element is started when receiving the first timing signal from said first integrating circuit, thereby starting said inverter; (h) a second integrating circuit starting the integrating operation when receiving the first timing signal from said first integrating circuit, said second integrating circuit generating a reference signal, the level of which is gradually increased toward a predetermined reference value; and (i) comparing means for comparing the detection signal from said input current detecting means with the reference signal from said second integrating circuit, thereby causing said control means to generate an inverter turn-off signal when the level of the reference signal is higher than that of the detection signal.