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POWER MIG 255
THEORY OF OPERATION
E-4 E-4
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CONSTANT VOLTAGE OUTPUT
The controlled DC output from the SCR rectifier
assembly is supplied to the power factor enhancement
choke which limits the rate at which the supply current
rises through the capacitors. The DC output from the
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
FIGURE E.4 — CONSTANT VOLTAGE OUTPUT.
LINE
SWITCH
RECONNECT
MAIN
TRANSFORMER
SNUBBER
BOARD
RECTIFIER
DIODE
BRIDGE
ARC
VOLTAGE
WIRE
SPEED
GAS
SOLENOID
FAN
MOTOR
CONTROL
BOARD
WIRE
DRIVE
MOTOR
TACH
GUN TRIGGER
FEEDBACK
115 VAC
30 VAC
G
A
T
E
S
I
G
N
A
L
SCR
RECTIFIER
POWER
ENHANCEMENT
CHOKE
OUTPUT
CHOKE
C
A
P
A
C
I
T
O
R
S
F
E
E
D
B
A
C
K
NEGATIVE
TERMINAL
POSITIVE
TERMINAL
SHUNT
power factor enhancement choke is filtered by the
capacitor bank resulting in a constant voltage DC out-
put. Since the output choke is in series with the posi-
tive leg of the rectifier and also in series with the gun
and welding load, a filtered constant voltage output is
applied to the output terminals of the machine.