Importance

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Abstract

A power supply apparatus for a plasma arc utilizing equipment providing an output current nearly equal to an input current includes a first converter for converting an AC voltage to a DC voltage. The DC voltage is converted to a high frequency voltage by an inverter. The output of the inverter is converted through a second converter to a DC voltage which is applied between a torch and a workpiece. A current detector detects an output current flowing between the second converter and the workpiece. A voltage detector detects an output voltage between the torch and the workpiece. A multiplier multiplies the output current and the output voltage to provide a signal representative of an output power. A comparator compares the output power representative signal with a first preset value. A signal from the current detector is applied to an error amplifier when the output power representative signal is smaller than the first preset value, and, otherwise, the output power representative signal is applied to the error amplifier. The error amplifier controls the inverter such that the signal applied to the error amplifier can be equal to a second preset value set by a setting device.

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First Claim