Precharge And Protection - Lincoln Electric PRO-CUT 55 Service Manual

E-3
INPUT
LINE INPUT
SWITCH RECTIFIER
AIR
PRESSURE
SWITCH
"A"
L
E
A
D
FAN
MOTORS
AUXILIARY
TRANSFORMER

PRECHARGE AND PROTECTION

The input voltage is rectified by the input rectifier. The
resultant DC voltage is applied, through the reconnect
switch, to the power board. The power board contains
precharging circuitry for the safe charging of the input
filter capacitors. Once the capacitors are precharged
and balanced the control board activates the CR1
input relay. This connects full input power to the filter
capacitors. When the filter capacitors are fully
charged they act as power supplies for the IGBT
switching circuit. The Insulated Gate Bipolar Tran-
sistors supply the main transformer primary winding
with DC current flow. See IGBT Operation discussion
and diagrams in this section.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
THEORY OF OPERATION
FIGURE E.3 – PRECHARGE AND PROTECTION
POWER BOARD
CR 1
RELAY
IGBT
CAPACITOR
R
E
IGBT
C
O
N
N
E
C
IGBT
T
TRANSFORMER
S
W
I
CAPACITOR
T
C
H
IGBT
P
R
O
T
CR 1
E IGBT
RELAY
C
GATE
DRIVE
T
SIGNALS
SIGNAL
I
O
N
SIGNAL
CONTROL BOARD
18/36VAC
A
R
I
E
R
THERMOSTATS A
D L
Y O
W
OUTPUT
CONTROL
DISPLAY BOARD
MAIN
TRANSFORMER
CURRENT
TRIGGER & SAFETY
ELECTRODE & TRANSFER
CURRENT FEEDBACK
PILOT ENABLE
ELECTRODE SOLENOID ENABLE
AIR SOLENOID ENABLE
T S
H
A
E
F
R
E
M
T
A
Y
L
The power board also monitors the filter capacitors for
voltage balance and under or overvoltage. If either
should occur, the appropriate signal is sent to the con-
trol board to deactivate the CR1 input relay.
machine output will also be disabled.
WORK
NOZZLE
ELECTRODE
TORCH
CONNECTOR
OUTPUT BOARD
E
L
E
C
T
R
O
D
E
CHOKE
S
O
PILOT
L
TRANSISTOR
E
N
O
I
D
TRIGGER & SAFETY
AIR
SOLENOID
12VAC
24VAC
E-3
The