DC power supply apparatus

A DC power supply apparatus comprising:

• an input-side rectifier adapted to be coupled to an AC power supply which can provide an AC voltage of a value and to rectify the AC voltage applied thereto;
• a constant voltage circuit receiving an output voltage of said input-side rectifier for converting said output voltage to a voltage having a predetermined value;
• an inverter for converting an output voltage of said constant voltage circuit to a high-frequency voltage and developing the high-frequency voltage between output terminals thereof;
• a transformer having a primary winding coupled between said output terminals of said inverter and having a secondary winding in which a voltage-transformed version of said high-frequency voltage is induced;
• and
• an output-side rectifier coupled to said secondary winding of said transformer for rectifying said voltage transformed version of high-frequency voltage for application to a load;
• wherein:
• said inverter includes first and second circuits connected in parallel between input terminals of said inverter;
• said first circuit comprising first and second semiconductor switching devices each having a conduction path and a control electrode, the conduction paths of said first and second semiconductor switching devices being rendered conductive when first and second control signals are applied to the control electrodes of said first and second semiconductor switching devices, respectively, while a voltage is being applied in a predetermined polarity across said conduction paths, the conduction paths of said first and second semiconductor switching devices being connected in series with each other;
• said second circuit comprising a pair of current conducting units connected in series with each other;
• the junction between said first and second semiconductor switching devices and the junction between said current conducting units providing said output terminals of said inverter, whereby said first and second semiconductor switching devices and said pair of current conducting units form a bridge circuit;
• said first circuit further comprising first and second diodes connected in parallel with the conduction paths of said first and second semiconductor switching devices, respectively, and first and second capacitors connected in parallel with said first and second diodes, respectively, each of said diodes being so poled as to be rendered conductive when a voltage is applied across the conduction path of the associated semiconductor switching device in a polarity opposite to said predetermined polarity;
• said inverter further comprising a control unit for providing alternately said first and second control signals respectively to said first and second semiconductor switching devices with a quiescent period disposed therebetween.