Abstract: An AC arc welding circuit for controlling current supplied to a welding electrode for welding thin metal pieces. A coupling circuit connects a capacitance circuit between a terminal of the secondary winding of a power supply transformer and the welding electrode. The other terminal of the secondary transformer is connected to the common electrode of the secondary winding which is, in turn, connected to a thin metal piece to be welded. The control circuit is provided with a sensing coil to sense the current flowing in the thin metal piece and to initiate a trigger pulse to switch a TRIAC to short-circuit the capacitance circuit during a predetermined short time as determined by the timing circuit so as to provide for a high voltage high current supply to the welding electrode during arc initiating when the electrode is spaced from the metal piece.