IE41317L - Electric arc welder. - Google Patents

Abstract

1473510 Automatic control of arc welding C MAULE 30 April 1974 [3 May 1973] 18827/74 Heading G3R The voltage or current supplied by a static D.C. arc welder is regulated by a feedback circuit which controls a mains voltage converter producing a variable frequency squarewave which is fed to the arc terminals by way of an isolating transformer, a rectifier and an inductor. The squarewave frequency is controlled in accordance with measured output voltage or current. As shown, an arc 9 is supplied with mains voltage over a rectifier bridge 1, switching circuit 2 which may include transistors 11-13 or gated rectifiers, a transformer 4, rectifiers 6, an inductor 7 and a current-sensing resistor 8. The sensed current signal causes an amplifier 22 to block or saturate a transistor 23, thus determining the switching period of an astable multi-vibrator 26, the output of which is fed through a trigger circuit 37 and amplifier transistor 45 to the primary winding of a transformer 17 which has secondary windings connected in the base-emitter circuits of transistors 11-13. The operation of the feedback loop is such that the pulses fed to transformer 4 are of constant width but variable frequency. A diode 48 and Zener diode 49 protect transistors 11-13 and 45 from over-voltages. Zener diodes 19-21 protect, transistors 11-13 from negative over-voltages, and also discharge the energy stored in transformer 4 when the transistors are blocked. [GB1473510A]