Patent ID: 6388232
Filing Date: 2002-05-14
Classification: B23K

Abstract:
A DC TIG welder operable at a set low current level under about 5 amperes in a welding circuit including an electrode separated from a workpiece by a gap, said welder having an output welding current adjustable above said low current and driven by a constant current power supply with a first rectifier having an output current controlled by the firing phase of SCRs in an SCR network, a second rectifier settable at said low current and a sensor for sensing arc voltage, said welder further comprising: a circuit to deactivate said SCRs when said output welding current is equal to or less than said set low current and an arc starting device including a high frequency generator connected in said welding circuit to pass a high frequency, high voltage current across said gap; a circuit for activating said high frequency generator upon starting of said welder and after said arc voltage is sensed to be greater than a first given value; a start pulse device activated simultaneously with the arc start by high frequency from said high frequency generator to cause said first rectifier to output a high current pulse by operation of said SCRs of said network; and, a termination circuit for deactivating said high frequency generator after said arc voltage is generally less than a second given value.