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Patent application title: METHODS AND APPARATUS FOR IMPROVED LOW CURRENT AC/DC TIG WELDING AND STARTING Inventors: IPC8 Class: AB23K910FI USPC Class: 21913051 Class name: Including arc-power supplies with predetermined time variation of arc voltage or current (e.g., programmed) pulsating or periodic output Publication date: 2013-10-10 Patent application number: 20130264321 0 Svia m i se Budi prvi meu svojim prijateljima kome se ovo svia. Sign up to receive free email alerts when patent applications with chosen keywords are published SIGN UP Abstract: A TIG welder and methodologies for providing an output welding current in a welding circuit. The welder has main and background power supplies. The main supply has an SCR network which selectively connects a transformer secondary winding to the welding circuit according to SCR control signals. The background supply is connected to the SCR network, which selectively connects the second power supply to the welding circuit according to the SCR control signals. The SCR network may have first and second SCRs operating according to first and second SCR control signals from a control circuit, where the control circuit is connected to the SCR network and the second power supply and selectively connects the SCR control signals to the SCR network according to the setpoint current value. Images included with this patent application: Claims: 1. A method of providing an output welding current through a gap in a welding circuit between an electrode and a workpiece according to a setpoint current value in an AC/DC TIG welder, said method comprising: providing a first power supply having a first.transformer secondary winding and an SCR network, said SCR network being connected between said first transformer secondary winding and said welding circuit; providing a second power supply connected to said SCR network; selectively connecting said first transformer secondary winding to said welding circuit using said SCR network during a first portion of a power half-cycle to provide a first current to said welding circuit; and selectively connecting said second power supply to said welding circuit through said SCR network of said first power supply during a remaining portion of said power half-cycle using said SCR network. 2. The method of claim 1, wherein selectively connecting said first transformer secondary winding to said welding circuit comprises operating at least one SCR in said SCR network in a conductive state according to said SCR control signal so as to connect said first transformer secondary winding to said welding circuit during said first portion of said power half-cycle. 3. The method of claim 2, wherein selectively connecting said second power supply to said welding circuit comprises latching said at least one SCR using current from said second power supply so as to maintain said at least one SCR in said conductive state during said remaining portion of said power half-cycle. 4. The method of clai