Abstract: A power supply apparatus for welders includes an input-side AC-to-DC converter for converting an input commercial AC voltage into a DC voltage, which is, in turn, converted to a high-frequency voltage in an inverter. The high-frequency voltage is transformed to a high-frequency voltage having a desired magnitude in a transformer. The transformed high-frequency voltage is then converted back to a DC voltage in an output-side high-frequency-to-DC converter. The DC voltage is developed between output terminals of the power supply apparatus. A current detector detects the current flowing through the output terminals and develops a detected-current representative signal. A voltage detector detects the voltage between the output terminals and develops a detected-voltage representative signal. A CPU has three control modes and controls, in a first mode, the inverter in such a manner that the current representative signal becomes equal to a reference-current representative signal.

Abstract: An inverter includes a series circuit of two current conducting units connected between two input terminals adapted to be connected to a DC power supply. Two first capacitors are connected in series between the two input terminals. A primary winding of a transformer is connected between the junction of the current conducting units and the junction of the first capacitors. Each of the current conducting units includes a parallel circuit of an IGBT, a diode and a second capacitor. The IGBT has a collector, an emitter and a gate and is rendered conductive when a control signal is applied to the gate while a voltage of a predetermined polarity is applied between the collector and the emitter. The diode is connected in inverse parallel with the IGBT. An inverter control circuit applies alternately the control signals to the respective IGBTs with a predetermined quiescent period disposed between the respective control signals applied.

Abstract: Power supply apparatus includes a converter which converts a commercial AC voltage into a DC voltage. An inverter converts the DC voltage into a high frequency voltage. The high frequency voltage is voltage-transformed by a transformer, and then rectified and smoothed by a rectifier and a smoothing reactor into a DC voltage. This DC voltage is applied between a workpiece and a torch. A high frequency voltage generator generates a high frequency voltage and applies it to a primary winding of a coupling transformer. A boosted high frequency voltage is induced in a first secondary winding and applied between the workpiece and the torch, so that arcing is initiated. The coupling transformer includes a second secondary winding in which another high frequency voltage is induced. The high frequency voltage induced in the second secondary winding is converted into a DC voltage by a diode and a smoothing capacitor for application between the workpiece and the torch, so that the arcing is sustained.