Abstract: A welding power supply includes a DC power supply circuit that outputs DC power, an inverter circuit provided with a plurality of switching elements and configured to receive the DC power from the DC power supply circuit and to output AC power, a current sensor that detects output current from the inverter circuit, and a controlling circuit that controls the DC power supply circuit and the inverter circuit. In switching the output polarity of the inverter circuit, the controlling circuit reduces the output of the DC power supply circuit, then provides a short-circuit state by setting all of the switching elements to ON, and then switches a switching element that was ON before the short-circuit state to OFF when the absolute value of an instantaneous value of the output current decreases to or below a threshold value.

Abstract: A welding power supply is configured to supply electric power to a coated electrode. The welding power supply includes a rectifying circuit that converts inputted AC power into DC power, and an inverter circuit that converts the DC power into AC power to be outputted to the coated electrode. The inverter circuit is configured to output a square-wave current.

Abstract: A power source applies an AC voltage between a welding torch and a workpiece. The power source includes an inverter circuit to switch between a positive polarity and an opposite polarity, a restriking circuit to apply a restriking voltage to an output of the inverter circuit when the positive polarity is switched to the opposite polarity, and a control circuit to control the restriking circuit. The restriking circuit includes a restriking capacitor to be charged with the restriking voltage, a charging circuit to charge the restriking capacitor with the restriking voltage, and a discharging circuit to discharge the restriking voltage in the restriking capacitor. The control circuit causes the charging circuit to start charging at a time of the opposite polarity, and to end charging after the opposite polarity is switched to the positive polarity.