This dc output is controlled by chopper technology, F. see chopper technology, Theory of operation – Lincoln Electric MULTI-WELD SVM151-A User Manual

Page 39: Chopper technology fundamentals

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CHOPPER TECHNOLOGY
FUNDAMENTALS

The new era of welding machines such as the Multi-
Weld 350 employ a technology whereby a DC source
is turned on and off (chopped up) at high speed, then
smoothed through an inductor to control an arc.

Hence the name “Chopper.” The biggest advantage of
chopper technology is the high-speed control of the
arc, similar to how inverter machines operate. A block
diagram for this is as follows:

In this system, current from a DC source such as the
MULTI-SOURCE is applied through a solid state switch
to an inductor. By turning the switch on and off, current

in the inductor and the arc can be controlled. The fol-
lowing diagram depicts the current flow in the system
when the switch is open and closed:

When the switch is closed, current is applied through
the inductor to the arc. When the switch opens, current
stored in the inductor sustains flow in the arc and
through the diode. The repetition rate of switch closure
is 20Khz, which allows ultra-fast control of the arc. By

varying the ratio of on time versus off time of the switch
(Duty Cycle), the current applied to the arc is con-
trolled. This is the basis for Chopper Technology:
Controlling the switch in such a way as to produce
superior welding.

E-9

THEORY OF OPERATION

MULTI-WELD 350