Chopper Technology Fundamentals - Lincoln Electric VANTAGE SVM178-B Service Manual

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CHOPPER TECHNOLOGY
FUNDAMENTALS
The new era of welding machines such as the Vantage
500, 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.
EXTERNAL DC
SOURCE
In this system, the engine drives a three-phase alter-
nator, which generates power that is rectified and
filtered to produce about 80VDC. The current is applied
through a solid state switch (IGBT) to an inductor. By
70-80VDC
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
THEORY OF OPERATION
Hence the name "Chopper." The biggest advantage of
chopper technology is the high-speed control of the
arc, similar to the inverter machines. A block diagram
for this is as follows:
SOLID STATE
SWITCH
ARC
CONTROL
turning the switch on and off, current in the inductor
and the arc can be controlled. The following diagram
depicts the current flow in the system when the switch
is open and closed.
SWITCH
DIODE
CURRENT WITH SWITCH CLOSED
varying the ratio of on time versus off time of the switch
(Duty Cycle), the current applied to the arc is con-
trolled.
Controlling the switch in such a way as to produce
superior welding.
VANTAGE® 500
INDUCTOR
AND DIODE
INDUCTOR
ARC
CURRENT WITH SWITCH OPEN
This is the basis for Chopper Technology:
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ARC