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SQUARE WAVE TIG 255
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E-4
THEORY OF OPERATION
LINE
SWITCH
R
E
C
O
N
N
E
C
T
MAIN
TRANSFORMER
X2
X1
POWER
FACTOR
CAPACITORS
FAN
115VAC
PROTECTION
SNUBBER
BOARD
ARC START
115 VAC
GATE SIGNALS
HI-FREQ
115 VAC
CONTROL
BOARD
LCD DISPLAY
KEYPAD
LED
BOARD
KEYPAD
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115 VAC
115 VAC
REMOTE
RECEPTACLE
115 VAC
RECEPTACLE
CONTROL
TRANSFORMER
24 VAC
18 VAC
16 VAC
HIGH FREQUENCY SPARK
WORK
ELECTRODE
HI-FREQ
TRANSFORMER
BY-PASS
BOARD
POLARITY SWITCH
(DC POSITION)
CHOKE
FEED BACK
GATE SIGNALS
AC
AC
DC+
DC-
SCR
BRIDGE
SHUNT
When the polarity switch is placed in either DC posi-
tion, the AC voltage from the main transformer sec-
ondary is applied to the SCR bridge. The SCR bridge
and choke circuits are connected in a conventional full
wave bridge and filter configuration, resulting in a con-
trolled DC output. Since the choke is in series with
the negative leg of the bridge and also in series with
the welding load, a filtered DC is applied to the
machine’s output studs.
DC WELDING OUTPUT
CHOKE
WORK
ELECTRODE
PRIMARY
1Ø
G
G
G
G
DC
DC WELDING CIRCUIT