D.C. POWER SUPPLY

摘要

A D.C. power supply for use in microwave ovens has a main circuit (100) and a control unit (200). In the main circuit (100) an A.C. mains voltage is rectified by a rectification circuit (120) and then is chopped at at high frequency by means of a switching element (112). The resultant voltage is smoothed by a capacitor (119) before applied to a magnetron (130). The control unit (200) functions to control an ON-OFF operation of the switching element (112), and includes four control circuits (240, 220, 260 and 280). The first control circuit (240) functions to vary the duty ratio of the control pulse in accordance with the rectified voltage level and the current flowing through switching element (112). The second control circuit (220) limits the period of time during which the switching element performs an ON-OFF operation in accordance with the level of the rectified voltage. The third and fourth control circuits (260, 280) are protective against excess currents and voltages respectively to prevent damage to the switching element and magnetron. By this circuit configuration, the magnetron (130) of the microwave oven is supplied with a continuously controllable D.C. voltage of a flat waveform.