Theory of operation, Ac welding output, Figure e.8 dc welding current generation – Lincoln Electric PRECISION TIG 275 SVM162-B User Manual
Page 44: Precision tig 275, Figure e.7 – ac welding output
E-6
E-6
PRECISION TIG 275
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 machineʼs
output work terminal. The other secondary lead (X2) is
connected to one of the AC connections of 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 appropri-
ate times, an AC square wave is developed and
applied to the output terminals. The bypass board pro-
tects the internal circuitry from interference.
THEORY OF OPERATION
FIGURE E.7 – AC WELDING OUTPUT
POWER
SWITCH
RE
CO
NN
EC
T
P
AN
EL
OPTIONAL POWER
FACTOR
POLARITY
SWITCH
BYPASS BOARD
WORK
FRONT
ELECTRODE
REAR
ELECTRODE
78
V
AC
X1
X2
AC
AC
DC
DC
SHUNT
CH
O
KE
HIGH FREQUENCY
TRANSFORMER
HIGH VOLTAGE
TRANSFORMER
THERMOSTAT
115 VAC
115 VAC
11
5 V
AC
FAN
GA
TE
LE
AD
S
FE
ED
BA
CK
GAS
SOLENOID
11
5 V
AC
11
5 V
AC
LED's
THERMOSTAT
20 VAC
20 VAC
CONTROL BOARD
BACKGROUND
CIRCUIT
FROM
CONTROL
BOARD
63
.5
VA
C
CORRECTION
CAPACITORS
REAR GANG
SCR
BRIDGE
ADVANCED CONTROL
PANEL RECEPTACLE
MINIMUM
OUTPUT
CONTROL
MAXIMUM
OUTPUT
CONTROL
PROTECTION
BOARD
REMOTE
RECEPTACLE
METER
STICK
TIG
SWITCH
BALANCE
CONTROL
POST
FLOW
LOCAL/REMOTE
SWITCH
FIGURE E.8 DC WELDING CURRENT GENERATION
G
CHOKE
ELECTRODE
WORK
DC
PRIMARY
10
G
G
G