Lincoln Electric INVERTEC SVM129-B - Manual (Page 29)

Section E-1 Section E-1
INVERTEC® STT® & STT® II
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, IGBT 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
TABLE OF CONTENTS
-THEORY OF OPERATION SECTION-
POSITIVE
OUTPUT
TERMINAL
TERMINAL
OUTPUT
NEGATIVE
CONTROL BOARD
IGBT
DRIVER
BOARD
P
O
W
E
R
B
O
A
R
D
FAN TRANS
T1
TRANS
T4
S
W
I
T
C
H
B
O
A
R
D
S
W
I
T
C
H
B
O
A
R
D
R
E
C
O
N
N
E
C
T
P
R
O
T
E
C
T
I
O
N
INPUT
RECTIFIER
LINE
SWITCH
CR1
CR2
B
O
A
R
D
D
R
I
V
E
R
B
O
A
R
D
PRE -
CHARGE
PRE -
CHARGE
CHOKE
CURRENT
SENSOR
IGBT
MODULE
1 OHM
PEAK
CURRENT
METER
BACK-
METER
PEAK
CURRENT
CONTROL
BACK-
CONTROL
HOT
START
CONTROL
WIRE
SIZE
SWITCH
WIRE
TYPE
SWITCH
VOLTAGE
SENSING
RECEPTACLE
REMOTE
CONTROL
RECEPTACLE
WIRE
RECEPTACLE
FEEDER
R
E
M
O
T
E
P
R
O
T
E
C
T
I
O
N
B
O
A
R
D
CURRENT
TRANS
T3
MAIN
TRANSFORMER
T2
115
VAC
18
VAC
2
4
V
A
C
"A"
LEAD
15VDC
T
H
E
R
M
O
S
T
A
T
CURRENT FEEDBACK
42VAC
VOLTAGE FEEDBACK
10VAC AND 6VAC
D
R
I
V
E
S
I
G
N
A
L
36VAC
GUN TRIGGER
LESS THAN 1VDC
PWM SIGNAL
PULSE TRANSFORMER SIGNAL
GROUND GROUND
FET
FET
FET
FET
CAP
CAP
TAILOUT
CONTROL
(STT II ONLY)
FIGURE E.1 – INVERTEC® STT® & STT® II
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