Lincoln Electric SVM136-A service manual Output CONTROL, Rectification and Feedback

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E-3 E-3

THEORY OF OPERATION

FIGURE E.3 – OUTPUT CONTROL, RECTIFICATION AND FEEDBACK

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CONTROL

TRANSFORMER

POWER

SWITCH MAIN

TRANSFORMER

R

E

C

O

N

N

E

C

T

INPUT

CONTACTOR

		T		115VAC
TO	REMOTE	E	S
	CONTROL	R	T
CONTROL		M
			R
BOARD		I		FAN
			I
		N
			P
		LA
			s	42VAC

OUTPUT

CONTROL

CONTROL BOARD

		F
G	S
		E
A	I
		E
T	G	D
E	N	B
	A	A
	L	C
	S	K

OUTPUT

CAPACITORS

SCR / DIODE

HYBRID BRIDGE

NEGATIVE

OUTPUT

TERMINAL

F

E

E

D

B

A

C

K

POSITIVE

OUTPUT

TERMINAL

SHUNT

14 PIN AMPHENOL

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OUTPUT CONTROL, RECTIFICATION AND FEEDBACK

The three-phase AC output from the main transformer secondary is rectified and controlled through the SCR/diode bridge. Output current and voltage is sensed at the shunt and output capacitors, respective- ly. This feedback information is processed in the con- trol board. The control board compares the commands of the output control (or remote control) with the feed- back information and sends the appropriate gate firing signals to the SCR/diode bridge. See SCR Operation in this section.

A "dry closure" of leads #2 and #4, either at the termi- nal strip or the 14 pin amphenol, signals the control board to apply gate firing signals to the SCR/diode bridge, which creates a DC voltage at the output of the bridge assembly. This output is filtered by the capacitors to reduce the ripple content of the wave- form. Thus, a smoother DC output is created. The choke, which is in series with the negative output ter- minal, stores energy and provides current filtering.

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NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

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