POWER MODULES AND FEED-
BACK
The external DC source voltage is applied to parallel
capacitors incorporated within each of the two Power
(Chopper) Modules. These capacitors function as fil-
ters and as power supplies for the IGBTs. See IGBT
Operation in this section. The IGBTs act as high-
speed switches operating at 20KHZ. These devices
are switched on and off by the Weld Control Board
through pulse width modulation gate signals. See
Pulse Width Modulation in this section. This
“chopped” DC output is applied through choke coils
and a shunt to the welding output terminals. The
chokes function as current filters. Free-wheeling
diodes are incorporated in the power circuit to provide
a current path for the stored energy in the chokes when
the IGBTs are turned off. See Chopper Technology in
this section.
Output voltage and current feedback information is fed
to the Weld Control Board. This information is sensed
from the output terminal circuits and the shunt. The
feedback information is processed by the Weld Control
Board, which regulates output voltage and current.
E-3 E-3
THEORY OF OPERATION
MULTI-WELD 350
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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
