Lincoln Electric SVM151-A service manual Chopper Technology Fundamentals, 70-80VDC

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THEORY OF OPERATION

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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:

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EXTERNAL DC	SOLID STATE	INDUCTOR	ARC
SOURCE	SWITCH	AND DIODE

ARC

CONTROL

In this system, current from a DC source such as the	in the inductor and the arc can be controlled. The fol-
MULTI-SOURCE is applied through a solid state switch	lowing diagram depicts the current flow in the system
to an inductor. By turning the switch on and off, current	when the switch is open and closed:

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SWITCH

70-80VDC

DIODE

INDUCTOR

ARC

CURRENT WITH SWITCH OPEN

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CURRENT WITH SWITCH CLOSED

When the switch is closed, current is applied through	varying the ratio of on time versus off time of the switch
the inductor to the arc. When the switch opens, current	(Duty Cycle),	the current applied to the arc is con-
stored in the inductor sustains flow in the arc and	trolled. This	is the basis for Chopper Technology:
through the diode. The repetition rate of switch closure	Controlling the switch in such a way as to produce
is 20Khz, which allows ultra-fast control of the arc. By	superior welding.

MULTI-WELD 350