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THEORY OF OPERATION
E-7 E-7
INVERTEC STT
FIGURE E.7 – POWER BOARD AND REMOTE PROTECTION BOARD
POWER BOARD
The power board creates a pulse transformer drive sig-
nal, which is derived from the PWM signal received
from the control board. See Pulse Width Modulation
discussion. This drive signal is applied to the primary
winding of the pulse transformer, which is located on
the driver board. The pulse transformer secondary
windings generate the proper gate pulse for the switch
board FETs. See Field Effect Transistor (FET)
Operation.
The power board supplies a 15VDC supply voltage for
the control board and also powers the input relays
(CR1 and CR2).
REMOTE PROTECTION BOARD
The remote protection board provides noise suppres-
sion and by-pass filtering to protect the internal circuit-
ry of the STT machine.
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)