Theory of operation, General description, Input voltage – Lincoln Electric INVERTEC SVM129-B User Manual
Page 30
GENERAL DESCRIPTION
The INVERTEC® STT® & STT® II is a 225 ampere,
inverter based, arc welding power supply specifically
designed for the Surface Tension Transfer (STT) weld-
ing process. It cannot be classified as either a constant
current (CC) or a constant voltage (CV) machine. The
STT produces current of a desired waveform to reduce
spatter and fumes. The STT process is optimized for
short - circuit GMAW welding only.
INPUT VOLTAGE
The INVERTEC® STT® & STT® II can be connected
for a variety of three-phase voltages. The initial input
power is applied to the STT through a line switch locat-
ed on the front of the machine. The AC input voltage is
applied to the input rectifier and the T1 auxiliary trans-
former. The T1 transformer develops the appropriate
AC voltages to operate the cooling fan, the power and
control boards. The T1 transformer also supplies pri-
mary voltage to the T4 auxiliary transformer as well as
42 VAC to an external wire feeder. The T4 transformer
supplies power to the IGBT drive board and the control
board.
THEORY OF OPERATION
E-2
E-2
INVERTEC® STT® & STT® II
FIGURE E.2 – INPUT VOLTAGE
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
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)