PURPOSE: To improve the durability of a relay by providing such a constitution as never operating the relay for connecting a resonance capacitor to an inverter circuit even when a small material detecting operation is repeated.
CONSTITUTION: A microcomputer 20 inputs the output of a small material detecting circuit 16 and the output of a pan detecting circuit 17, controls the operation of an inverter circuit 11 through a drive circuit 18, and also switches a relay 12 through a driving circuit 19 to operate the inverter circuit 11 in the state of an interter I and in the state of an inverter II. When the small material detecting circuit 16 judges that a load is not a small material after starting in the state of the inverter I, the inverter circuit is switched to the state of the inverter II, and then to the state of the inverter II in which the small material is judged in this state. The inverter I detects the small material more easily than the inverter II. Thus, even if the small material detecting operation is repeated, the relay 12 is never operated.
HATTORI KENJI
IWAI TOSHIAKI
NOMA HIROBUMI
