Theory Of Operation; General Description - Lincoln Electric SQUARE WAVE TIG 175 Service Manual

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GENERAL DESCRIPTION

The Square Wave TIG 175 is a constant current, single range AC/DC TIG (GTAW) arc welding power source with
a built-in arc starter/stabilizer. It also has stick welding (SMAW) capability. The Square Wave TIG 175 is recom-
mended for the TIG (GTAW) and stick (SMAW) welding processes within its output capacity of 12 to 175 amps,
on both AC and DC polarity.
INPUT
POWER
SWITCH
H1
H2
H3
FAN
RECEPTACLE
INPUT POWER CIRCUIT
The desired single-phase input power is connected to
the TIG 175 through an input power switch located in
the front panel of the machine. The machine can be
configured for either 230VAC or 208VAC input voltage
by connecting the appropriate lead (H2 or H3) to the
input power switch. When the input power switch is
turned "ON" the input voltage is applied directly to the
primary of the main transformer.
The main transformer changes the high voltage, low
current input power to a low voltage, high current out-
put which is available at the main secondary winding
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.

THEORY OF OPERATION

FIGURE E.2 Main Transformer and Input Power
MAIN
TRANSFORMER
X1
X2
18VAC
18VAC
115VAC
REMOTE
THERMAL
LIGHT
SQUARE WAVE TIG 175
BY-PASS
BOARD
POLARITY
SWITCH
C
H
O
AC
DC+
K
SCR
E
BRIDGE
SHUNT
DC-
AC
F
E
E
D
B
A
C
K
CONTROL
BOARD
THERMO-
GAS OUTPUT
STATS
VALVE CONTROL
(X1 and X2). In addition three auxiliary windings are
incorporated in the main transformer.
winding supplies power to the fan motor and also,
through the control board, powers the gas solenoid
valve and the high voltage transformer. The 18VAC
winding provides power to the trigger circuitry. The
other 18VAC winding is rectified and regulated to a
15VDC supply which operates the circuitry on the con-
trol board.
WORK
ELECTRODE
HI-FREQUENCY
TRANSFORMER
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115VAC
POWER
"ON"
LIGHT
MODE
SWITCH
The 115VAC
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