Lincoln Electric SVM175-A Chopper Technology Fundamentals, 90 VDC, Diode, Inductor ARC

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E-7		THEORY OF OPERATION		E-7
	CHOPPER TECHNOLOGY
	FUNDAMENTALS		Hence the name “Chopper.” The biggest advantage of
	The new era of welding machines such as the Ranger
	305D employ a technology whereby a DC source is		chopper technology is the high-speed control of the
	turned on and off (chopped up) at high speed, then		arc, similar to the inverter machines. A block diagram
	smoothed through an inductor to control an arc.		for this is as follows:

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3PHASE ALTERNATOR

DC RECTIFIER

AND FILTER

SOLID STATE

SWITCH

ARC

CONTROL

INDUCTOR AND DIODE

ARC

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In this system, the engine drives a three-phase alter-	the switch on and off, current in the inductor and the
nator, which generates power that is rectified and fil-	arc can be controlled. The following diagram depicts
tered to produce about 90 VDC. The current is applied	the current flow in the system when the switch is open
through a solid state switch to an inductor. By turning	and closed:

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90 VDC	SWITCH
	DIODE

INDUCTOR

ARC

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CURRENT WITH SWITCH OPEN

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.

RANGER 305D