Theory Of Operation .............................................................................................................Section E - Lincoln Electric INVERTEC STT Series Service Manual

Section E-1
-THEORY OF OPERATION SECTION-
Theory of Operation .............................................................................................................Section E
General Description ...............................................................................................................E-2
Input Voltage..........................................................................................................................E-2
Reconnect, Protection Board, Rectification and Precharge ..................................................E-3
Switch Boards........................................................................................................................E-4
Main Transformer, Output Rectification and Choke...............................................................E-5
Control Board, Darlington Drive and Module.........................................................................E-6
Power Board ..........................................................................................................................E-7
Remote Protection Board ......................................................................................................E-7
Field Effect Transistor (FET) Operation.................................................................................E-8
Pulse Width Modulation .........................................................................................................E-9
Minimum Output ..............................................................................................................E-9
Maximum Output .............................................................................................................E-9
Protective Circuits................................................................................................................E-10
Overload Protection.......................................................................................................E-10
Thermal Protection ........................................................................................................E-10
S
W
I
T
C
H
LINE INPUT
SWITCH RECTIFIER
CR1
"A"
LEAD
CR2
115 VAC 18
FAN
VAC P B
TRANS
O O
T1
W A
115
E R
VAC
2
R D
4
V
A
TRANS
C
T4
T
H
E
R
PWM SIGNAL
M
O
S
15VDC
T
A
T
GUN TRIGGER
36VAC
PEAK
CURRENT
METER
TABLE OF CONTENTS
B
FET
O
A
CAP
R
FET
D
PRE -
CHARGE
R
P D
B
E
R
B
R
C O O
CURRENT
T O I
O A
TRANS
E
A V T3
N
C R
N T R E
D
I
E
D R
O
C
N
T
PRE -
CHARGE
B
S
FET
W
O
I
A
CAP
T
R
C
FET
H D
LESS THAN 1VDC
PULSE TRANSFORMER SIGNAL
CONTROL BOARD
WIRE
BACK- WIRE
PEAK HOT BACK-
GROUND SIZE TYPE
CURRENT
START GROUND
METER SWITCH SWITCH
CONTROL CONTROL
CONTROL
FIGURE E.1 - INVERTEC STT
INVERTEC STT
MAIN
TRANSFORMER
T2
CURRENT
SENSOR
CHOKE
CURRENT FEEDBACK
DARLINGTON
DRIVER
BOARD
VOLTAGE FEEDBACK
10VAC AND 6VAC
42VAC
Section E-1
POSITIVE
OUTPUT
TERMINAL
1 OHM
DARLINGTON NEGATIVE
MODULE OUTPUT
TERMINAL
R VOLTAGE
SENSING
E
RECEPTACLE
M
O
D
T
R
REMOTE
I E
B CONTROL
V
RECEPTACLE
E
P O
R
A
S
I O
R
G
T
N
D
E
A
C
L
T
WIRE
I FEEDER
RECEPTACLE
O
N