Current control for pulse arc welding

Claim 1

In a pulse arc welding device for periodically superimposing a pulse current from a pulse current source on a D.C. welding current from a D.C. source to be fed between a welding electrode and a workpiece to be welded, the improvement which comprises a pulse current detector; a thyristor; a transformer connected between said pulse current source and said electrode and said workpiece through said pulse current detector and said thyristor; a variable voltage reference device including rectifier means connected to said transformer for rectifying a voltage across a secondary winding of said transformer, a diode connected to the output of said rectifier means and a potentiometer having a movable tap and being connected in parallel to said diode for providing a reference voltage; comparison means including a reference capacitor for comparing a voltage corresponding to the current detected by said pulse current detector and said reference voltage, said capacitor being connected to said movable tap and between the output terminals of said pulse current detector; adjusting means for adjusting the pulse current supplied to said welding electrode and workpiece by control of said thyristor including a resistor, a uni-junction transistor and a pulse transformer connected in series across said potentiometer, said pulse transformer having an output winding connected with the cathode and gate terminals of said thyristor, and means for supplying an electrical signal indicative of the difference between said detected voltage and said reference voltage to said adjusting means, including a transistor, a resistor and a second capacitor connected in series across said potentiometer, the base of said transistor being connected to said reference capacitor, the emitter of said unijunction transistor being connected to a common junction point between said resistor and said second capacitor.