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TABLE OF CONTENTS-THEORY OF OPERATION SECTION
E-1 E-1
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PRECISION TIG® 225
TheoryofOperation .....................................................................E-1
GeneralDescription ...................................................................E-2
InputPowerCircuit....................................................................E-2
Output Rectification and Feedback Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-3
High Voltage/High Frequency Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-4
DCWeldingOutput ...................................................................E-5
ACWeldingOutput ...................................................................E-6
SCROperation.......................................................................E-7
ProtectiveCircuits ....................................................................E-8
ThermalProtection....................................................................E-8
OverloadProtection ...................................................................E-8
FIGURE E.1 PRECISION TIG® 225 BLOCK LOGIC DIAGRAM
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
THERMO-
STATS
OUTPUT
CONTROL
MODE
SWITCH
POWER
"ON"
DIGITAL
DISPLAY
F
E
E
D
B
A
C
K
AUTO
BALANCE
LED
TIG
LED
STICK
LED
PULSE
FREQ.
LED
BYPASS
ASBLY
AC
BALANCE
CONTROL
PULSE
CONTROL
POSTFLOW
CONTROL
115 VAC
Receptacle
Circuit Breaker
Protected