Abstract: A power source apparatus for microwave oven includes a half-bridge converter including a series connection of switching elements, a series connection of resonance capacitors, and a high frequency transformer having a primary winding and a secondary winding, and the half-bridge converter is driven by an output of a diode bridge which receives a commercial power source of 200 V. A current transformer detects a current of the primary winding. A control circuit compares a voltage equal to an average value of the current detected by the current transformer and a voltage set by a microcomputer, and controls the switching elements at a frequency in proportion to a magnitude of a difference of the both voltages, whereby a high frequency high voltage is induced on the secondary winding and applied to a voltage doubler rectifying circuit, and then a direct current high voltage is applied to a magnetron.

Abstract: An induction heating apparatus comprises an SEPP inverter including two transistors (Q1, Q2) connected in series, one transistor (Q1) being connected to a high electric potential end of a direct current power source (DB1) and the other transistor (Q2) being connected to a low electric potential end. A series circuit of a induction heating coil (L1) and a resonance capacitor (C1) is connected in parallel with one transistor (Q1) and freewheel diodes (D1, D2) are connected in anti-parallel with two transistors (Q1, Q2), respectively. A controlling circuit (71) turns one transistor (Q1) on/off in a predetermined cycle and a controlling circuit (72) turns the other transistor (Q2) on in an arbitrary time period in an off interval of one transistor (Q1) so that an input current to the series circuit is controlled.