| 摘要 |
PURPOSE:To reduce the size of a power source device by connecting the 2nd reverse blocking switch in series to the circuit of the 1st reverse blocking semiconductor switch connected in series to the transformer of a welding machine. CONSTITUTION:The 1st and 2nd reverse blocking semiconductor switches 30, 28 and the transformer 32 of the welding machine are connected in series to an AC power source 24. Electrodes 34, 34 are connected to the secondary side of the transformer 32. The 2nd switch 28 is fired in the phase position where a transient phenomenon does not arise. The 1st switch 30 is so controlled by a control part 40 as to fire within the half cycle of the phase current to be passed by firing of the 2nd switch. The use of the switch 28 having the smaller rating than the rating of the switch 30 is made possible by the above-mentioned method. The power source device itself is thus made smaller in size and lower in cost. |
