Patent ID: 8476554

Claim:
A TIG welder operable to provide an output welding current through a gap in a welding circuit between an electrode and a workpiece according to a setpoint current value, said welder comprising: a first power supply comprising a first transformer secondary winding; an SCR network connected to said first transformer secondary winding, said SCR network being operable to selectively connect said first transformer secondary winding to said welding circuit according to SCR control signals so as to provide a first current to said welding circuit; a second power supply connected to said SCR network, said SCR network being operable to selectively connect said second power supply to said welding circuit according to said SCR control signals so as to provide a second current to said welding circuit through at least one SCR in said SCR network of said first power supply; a control circuit connected to said SCR network and to said second power supply and operable to selectively connect said SCR control signals to said SCR network according to said setpoint current value; and an AC/DC switch with a first switch condition and a second opposite switch condition; wherein said welder is operable in an AC mode to provide an AC output welding current through said gap in said welding circuit according to said setpoint current value when said AC/DC switch is in said first switch condition, and is operable in a DC mode to provide a DC output welding current through said gap in said welding circuit according to said setpoint current value when said AC/DC switch is in said second switch condition; wherein said SCR network is operable in said AC mode to provide current of a first polarity to said welding circuit from at least one of said first and second power supplies in a first half-cycle, and to provide current of a second polarity to said welding circuit from at least one of said first and second power supplies in a second half-cycle according to said setpoint current value; and wherein said SCR network is operable in said DC mode to provide current of one of said first and second polarities to said welding circuit from at least one of said first and second power supplies according to said setpoint current value.