Lincoln Electric 11141 Service Manual page 41

E-3
Input switch
Auxiliary
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P
Transformer
o
220 VAC
w
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r
W
a
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42VAC
4
220
0
5
Receptacle
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n DC
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Bus
y
Board
SWITCH BOARD &
MAIN TRANSFORMER
There is one switch board in the POWER WAVE
355M/405M. This board incorporates two pairs of
input capacitors, two insulated gate bipolar transistor
(IGBT) switching circuits, a fan motor drive circuit, and
a voltage/frequency capacitor feedback circuit. The
two capacitors in a pair are always in series with each
other. When the reconnect switch is in the lower volt-
age position the capacitor pairs are in parallel - that is,
two series capacitors in parallel with two series capac-
itors. When the reconnect switch is in the high voltage
position the two capacitor pairs are in series or, four
capacitors in series. This is required to accommodate
the higher input voltages.
When the input capacitors are fully charged they act as
power supplies for the IGBT switching circuits. When
welding output is required the Insulated Gate Bipolar
Transistors switch the DC power from the input capac-
itors, "on and off" thus supplying a pulsed DC current
to the main transformer primary windings. See IGBT
Operation Discussion and Diagrams in this section.
Each IGBT switching circuit feeds current to a sepa-
rate, oppositely wound primary winding in the main
transformer. The reverse directions of current flow
through the main transformer primaries and the offset
timing of the IGBT switching circuits induce an
THEORY OF OPERATION
FIGURE E.3 – SWITCH BOARD & MAIN TRANSFORMER
Main Switch Board
Input
Rectifier
Reconnect
Switch
Fan
115VAC Fan Supply
V/F Capacitor Feedback (2)
Machine Control Supply
40VDC
+15VDC, -15VDC, +5VDC
Power
Board
RS232 Supply +5VDC
Can Supply +5VDC
40VDC
POWER WAVE
Primary
Current
Sensor
Primary
Current
Sensor
Primary Current Feedback(2)
Input Relay Control
Soft Start Control
Control Board
Arc
Electrode
Link
Sense
Wire
Feeder
Recp.
Thermostats
2
To
F
AC square wave output signal at the secondary of the
®
main transformer. The two current transformers (CT)
located on the switch board monitor these primary cur-
rents. If the primary currents become abnormally high
the control board will shut off the IGBTs, thus disabling
the machine output. The DC current flow through each
primary winding is clamped back to each respective
input capacitor when the IGBTs are turned off. This is
needed due to the inductance of the transformer pri-
mary winding. The firing of the two switch boards
occurs during halves of a 50 microsecond interval, cre-
ating a constant 20 KHZ output. In some low open cir-
cuit Tig modes the firing frequency is reduced to 5KHZ.
The POWER WAVE ®
needed) circuit. The fan operates when the welding
output terminals are energized or when a thermal over
temperature condition exists. Once the fan is activat-
ed it will remain on for a minimum of five minutes. The
fan driver circuit is housed on the switch board but it is
activated by a signal from the control board.
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
® 355M/405M
To Control
Board
Positive
Output
Terminal
Choke
Negative
Output
Terminal
Yellow
Thermal
LED
Status
Red/Green
LED
21 Lead
Voltage
R232
Sense
Connector
Recp.
355M/405M has a F.A.N. (fan as
E-3