Lincoln Electric 11519 Service Manual page 42

E-4
AUX
115 VAC
LINE
SWITCH
RECONNECT
TRANSFORMER
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
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.
THEORY OF OPERATION
FIGURE E.4 — CONSTANT VOLTAGE OUTPUT
GAS
MOTOR
SOLENOID
WIRE
SPEED
CONTROL
ARC
BOARD
VOLTAGE
RECTIFIER
DIODE
G
BRIDGE
A
T
30 VAC
E
SNUBBER
S
BOARD
I
G
N
A
L
POWER
ENHANCEMENT
CHOKE
MAIN
SCR
RECTIFIER
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
Power MIG® 255XT
SPOOL
FAN
GUN
WIRE
DRIVE
MOTOR
TACH
TIMER ASSEMBLY
GUN TRIGGER
FEEDBACK
C OUTPUT
POSITIVE
F
A CHOKE
TERMINAL
E
P
E
A
D
C
B
I
A
T
C
O
NEGATIVE
K
R
TERMINAL
S
SHUNT
E-4