Lincoln Electric INVERTEC V275-S Service Manual page 25

E-3
FIGURE E.3 – MAIN IGBT SWITCH BOARD & MAIN TRANSFORMER
Input Switch
Input
& 100A Breaker
Rectifier
+
-
-
Aux.
Trans
Fan
Relay
Fan
Fan
Motor Motor
230VAC
230VAC
6
Pin
Amphenol
SWITCH BOARD
TRANSFORMER
There is one switch board in the Invertec V275-S. This
board incorporates two input capacitors, two insulat-
ed gate bipolar transistor (IGBT) switching circuits, a
precharge circuit, an over and under voltage protec-
tion circuit and two isolated +15VDC supplies that are
derived from the input capacitors. The two +15VDC
supplies are utilized by the electronic circuitry housed
on the Switch Board.
When the reconnect switch is in the lower voltage
position the two input capacitors are in parallel. When
the reconnect switch is in the higher voltage position
the two input capacitors are in series. This series con-
figuration is required to accommodate the higher input
voltages. Thus, the higher input voltage is shared
between the two capacitors. When the input capaci-
tors 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 capacitors "on and off"
thus supplying a pulsed DC current to the main trans-
former primary windings.
THEORY OF OPERATION
Main Switch Board
Reconnect
Switch
IGBT Drive Signal
Precharge Relay Control
To
Shut Down Signal
Fan
Motors
18 VAC
Relay Control
AND MAIN
V275-S
#1 Primary
Current
Feedback
To Control
Board
#2 Primary
Current
Feedback
Output
Diodes
#1 Primary
Current
Feedback
Control Board
Hot
Arc
Output
Mode
Start
Force Control
See IGBT Operation and Discussion 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 AC
square wave output signal at the secondary of the
main transformer. The two current transformers (CT),
located on the transformers primary winding leads,
monitor the two primary winding currents. If the pri-
mary currents become abnormally high the control
board will shut off the IGBTs, thus disabling the
machine's 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 transformers primary windings.
The firing of the two IGBT switching circuits occurs
during halves of a 33 microsecond interval, creating a
30 KHZ switched output Due to the full wave rectifi-
cation of the transformers secondary output voltage a
60KHZ DC output is presented at the machine's out-
put terminals.
E-3
Choke
Positive
+
Output
Terminal
Negative
-
Shunt
Output
Terminal
Thermostats
Thermo.
LED
Local
Remote