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THEORY OF OPERATION
E-4 E-4
INVERTEC STT
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
FIGURE E.4 – SWITCH BOARDS
SWITCH BOARDS
There are two switch boards in the Invertec STT, each
containing an input filter capacitor. The capacitors are
connected in parallel when the machine is connected
for "low" input voltage. The capacitors are connected
in series when the reconnect switch is configured for
"high" input voltage. When the capacitors are fully
charged, they act as power supplies for the switch
boards. The switch boards contain the Field Effect
Transistors (FETs) which, when switched on, supply
the main transformer primary windings with DC current
flow. See Field Effect Transistor (FET) Operation
discussion and diagrams. See Figure E.4.
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)