Ac Welding Output - Lincoln Electric SQUARE WAVE TIG 255 SVM100-A Service Manual

E-5
LINE
MAIN
SWITCH
TRANSFORMER
R
E
C
O
N
N
E
C
T
POWER
FACTOR
CAPACITORS
115VAC
FAN
115 VAC
RECEPTACLE
By rotating the polarity switch to the AC position the
welding power circuit is changed. One lead (X2) of
the main transformer secondary is connected to the
machine's output work stud. The other secondary
lead (X1) is connected to one of the AC connections
on the SCR bridge. The electrode stud is connected
PRIMARY
1Ø
SQUARE WAVE TIG 255
THEORY OF OPERATION

AC WELDING OUTPUT

POLARITY SWITCH
(AC POSITION)
AC DC+
X2
SCR
BRIDGE
X1
AC DC-
ARC START
115 VAC
PROTECTION
SNUBBER
GATE SIGNALS
BOARD
HI-FREQ
115 VAC
CONTROL
TRANSFORMER
115 VAC
REMOTE
RECEPTACLE
G
G
AC WELDING CIRCUIT
BY-PASS
BOARD
SHUNT
CHOKE
LCD DISPLAY
CONTROL
BOARD
24 VAC
18 VAC
16 VAC
HIGH VOLTAGE
HIGH FREQUENCY SPARK
TRANSFORMER
CIRCUIT
to the other AC side of the bridge. The choke is now
electrically across the negative and positive SCR
bridge connections. Due to the ability of the choke to
store energy and the SCR's ability to turn on at the
appropriate times, an AC Square Wave is developed
and applied to the output studs.
CHOKE
G
G
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
KEYPAD
LED
BOARD
KEYPAD
ELECTRODE
WORK
AC DC