Power supply unit for arc processing

A power supply unit for arc processing for a commercial AC power supply, in which either of high or low voltages inputs of approximately 1:2 ratio is selectively supplied as an input, the AC input is, after being rectified into DC power, inversely converted into a high frequency AC power by an inverter circuit employing switching elements, and then converted into a power suitable for arc processing comprising:

• three rectifying circuits connected in parallel, and each rectifying circuit comprising three diodes connected in series by connection points between the three series connected diodes;
• the AC power supply having input terminals and each input terminal of the commercial power supply being connected to a first one of the series connection points of the three diodes forming a corresponding rectifying circuit;
• two capacitors connected by a connecting point and arranged in series between two output terminals of the three rectifying circuits;
• three input voltage change-over circuits, each of which comprises a capacitor and a voltage change-over switch connected in series between a second one of the series connection points of the three diodes forming the corresponding rectifying circuit and the first series connection point of one of other rectifying circuits, each voltage change-over switch being closed at the low voltage input and opened at the high voltage input;
• a single phase input voltage change-over circuit arranged to connect a connection point of the two series capacitors to one of the input terminals and to cut off one of the remaining input terminals at a single phase low voltage input, and to cut off the connection with said capacitors at a single phase high voltage input;
• and
• an inverter circuit for said inverse conversion connected in parallel to the two series capacitors.