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Section E-1 Section E-1
SQUARE WAVE TIG 275
TABLE OF CONTENTS
- THEORY OF OPERATION SECTION -
Theory of Operation .............................................................................................................Section E
General Description ....................................................................................................................E-2
Input Power Circuit......................................................................................................................E-2
Output Rectification, Control Board and Feedback ....................................................................E-3
High Voltage/High Frequency Circuit..........................................................................................E-4
DC Welding Output .....................................................................................................................E-5
AC Welding Output .....................................................................................................................E-6
SCR Operation............................................................................................................................E-7
Protective Circuits .......................................................................................................................E-8
Thermal Protection ...............................................................................................................E-8
Overload Protection..............................................................................................................E-8
INPUT
POWER
SWITCH
MAIN
TRANSFORMER
POLARITY
SWITCH
SCR
BRIDGE
X1
X2
AC
AC
DC+
DC-
CONTROL
BOARD
18VAC
18VAC
115VAC
FAN
REMOTE
RECEPTACLE
H1
H2
H3
SHUNT
115VAC
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
BY-PASS
BOARD
HI-FREQUENCY
TRANSFORMER
C
H
O
K
E
WORK
ELECTRODE
THERMAL
LIGHT
GAS
VALVE
OUTPUT
CONTROL
MODE
SWITCH
F
E
E
D
B
A
C
K
H4
"A"
RECONNECT
PANEL
23VAC
DOWNSLOPE
CONTROL
POSTFLOW
CONTROL
BALANCE
CONTROL
THERMOSTATS
115VAC
RECEPTACLE
FIGURE E.1 - SQUARE WAVE TIG 275 BLOCK LOGIC DIAGRAM