METHOD AND DEVICE FOR CONTROLLING ELECTRIC CURRENT IN ARC WELDING POWER SOURCE

摘要

PURPOSE:To prevent arc breakage without providing a base power source and to simplify circuit constitution by changing over control of welding current to constant current control to maintain the welding current at a set value when the welding current decreases to the set current value or below. CONSTITUTION:When an arc voltage VA is increased by a disturbance, a differential signal SDV heads toward a negative direction to shorten the positive pulse width of a pulse signal SP. As a result, the conducting width of a switch SW is shortened and welding voltage IW is decreased. When the feedback signal If of welding current IW is below a set current value IS, a differential signal SDI>0 is attained. Since the differential signal SDV 0, SDI>SDV is obtained and the output VM=SDI of a max. value selecting circuit 7 is attained with the widened positive pulse width of the pulse signal SP. As a result, the conducting width of the switch SW is increased and the welding current IW is increased and is maintained at the value conforming to the set value IS. The generation of arc breakage is consequently prevented.