Lincoln Electric SQUARE WAVE TIG 355 Service Manual page 45

TABLE OF CONTENTS-THEORY OF OPERATION SECTION
E-1
Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-1
General Description And Input Power Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .E-2
Output Rectification And Feedback Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .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
FIGURE E.1 SQUARE WAVE TIG BLOCK LOGIC DIAGRAM
HIGH FREQUENCY SPARK
ELECTRODE SENSE
PANEL
SWITCHES
HIGH VOLTAGE
115VAC
TRANSFORMER
REMOTE
CIRCUIT
FEED - THRU
RECEPTACLE
BOARD
GAS/WATER
SOLENOIDS
115VAC
INTERLOCK
115VAC
FANS 115VAC
RECEPTACLE
CONTROL TRANSFORMER
INPUT
R
CONTACTOR
E
C
O
N
N
E
C
T
START/
STOP
PILOT
TRANSFORMER
UPPER
LOWER
DISPLAY
CONTROL
CONTROL
BOARD
PANEL PANEL
SCR GATE COMMANDS
ELECTRODE
SENSE
15VDC
CONTROL
TRIGGER
BOARD
REMOTE INTERLOCK
COMMANDS
HI-FREQ/ WATER/GAS
COMMANDS
INTERLOCK
HI-FREQ AND GAS/WATER
115VAC -
115VAC
AC
AC
POWER
FACTOR
CAPACITORS
POLARITY
SWITCH
MAIN
TRANSFORMER
SQUARE WAVE TIG 355
STATUS
BOARD
POWER
BOARD
SNUBBER
BOARD
DC-
C
H
DC+
O
K
E
SHUNT
BY-PASS
BOARDS
ELECTRODE
HI-FREQ
TRANSFORMER
E-1
WORK