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

LINE
MAIN
SWITCH
TRANSFORMER
R
E
C
O
N
N
E
C
T
POWER
FACTOR
CAPACITORS
115VAC
FAN
115 VAC
RECEPTACLE
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-
PRIMARY
1Ø
THEORY OF OPERATION

DC WELDING OUTPUT

POLARITY SWITCH
(DC 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
G
G
DC WELDING CIRCUIT
BY-PASS
BOARD
SHUNT
CHOKE
LCD DISPLAY
CONTROL
BOARD
24 VAC
18 VAC
16 VAC
HIGH VOLTAGE
HIGH FREQUENCY SPARK
TRANSFORMER
CIRCUIT
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.
CHOKE
WORK
HI-FREQ
TRANSFORMER
ELECTRODE
KEYPAD
LED
BOARD
KEYPAD
ELECTRODE
WORK
SQUARE WAVE TIG 255
E-4
DC