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THEORY OF OPERATION
E-6 E-6
PRECISION TIG® 225
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AC WELDING OUTPUT
Rotating the polarity switch to the AC position changes the welding power circuit. One lead (X1) of the main
transformer secondary is connected to the machine output work terminal. The other secondary lead (X2) is con-
nected to one of the AC connections on the SCR bridge. The electrode terminal is connected to the other AC
side of the bridge. The choke is now electrically across the negative and positive SCR bridge connections. With
the ability of the choke to store energy and the SCRs to turn on at the appropriate times, an AC square wave is
developed and applied to the output terminals.
FIGURE E.6 AC Square Wave Welding Current Generation.
CHOKE
WORK
ELECTRODE
PRIMARY
1Ø
G
G
G
G
DC