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E-2
THEORY OF OPERATION
E-2
IDEALARC SP-250
OUTPUT RECTIFICATION AND FEED-
BACK CONTROL
The AC output from the main transformer secondary
weld winding is rectified and controlled through the
SCR rectifier assembly. Output voltage and current
are sensed at the shunt and output terminals and fed
back to the control board. The control board compares
the commands of the keypad (or gun thumb switch)
with the feedback signals. The appropriate gate firing
pulses are generated by the control board and applied
to the SCR rectifier assembly. The control board con-
trols the firing of the SCRs, thus controlling the output
of the machine. See SCR Operation. The control
board also powers and commands the keypad, the
LCD Display, the piezo alarm, the gas solenoid and the
wire drive motor.
Figure E.3 - Output Rectification and Feedback Control
POWER SUPPLY OPERATION (CONTINUED)
LINE
SWITCH
MAIN
TRANSFORMER
RECONNECT
FAN
MOTORS
SCR
RECTIFIER
C
A
P
A
C
I
T
O
R
S
SHUNT
CHOKE
WIRE
DRIVE
MOTOR
TACH
POSITIVE
TERMINAL
NEGATIVE
TERMINAL
GAS
SOLENOID
PIEZO
ALARM
KEYPAD
CONTROL BOARD
FEEDBACK
GUN TRIGGER AND THUMB SWITCH
F
E
E
D
B
A
C
K
G
A
T
E
I
G
N
S
A
L
LCD
DISPLAY
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
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