DC or AC arc welding supply - with rectifier and inverter for current zero passage driven firing control

摘要

A c.c. and/or a.c. arc welding current supply uses an inverter to produce an a.c. of much higher frequency than the mains supply. A transformer or a rectifier connect up electrode and workpiece to this supply. The chopper units for the thyristors of the inverter receive zero passage signals which are picked up from free-running circuits of the thyristors. These circuits include primary windings of at least one current transformer, preferably a saturable pulse transformer which is joined through its secondary winding to the chopper control. This prevents short-circuits by too early a firing of a blocked thyristor, due to temporary collapse of the magnetic field in the pulse transformer caused by the welding current flucturations.