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THEORY OF OPERATION
E-6 E-6
INVERTEC STT
FIGURE E.6 – CONTROL BOARD, IGBT DRIVE AND MODULE
CONTROL BOARD, IGBT DRIVE
AND MODULE
The control board monitors the directives of the various
controls and compares these commands to the current
and voltage feedback information received from the
current sensor and voltage sensing receptacle. This
data is processed and the suitable PWM signal is sent
to the power board. (See Pulse Width Modulation
discussion).
The control board also determines when the IGBT
module should be switched OFF to reduce weld spat-
ter and fumes. The appropriate signal is sent to the
IGBT drive board which then applies, or removes, the
gate drive signal to the IGBT module. When the IGBT
module is in the OFF state, the welding current must
pass through the one ohm resistance. This reduces
the current and, subsequently, spatter and fumes.
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
RECEPTACL
E
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)