Lincoln Electric SVM118-A service manual Table of Contents Theory of Operation Section

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Section E-1Section E-1

TABLE OF CONTENTS

-THEORY OF OPERATION SECTION-

Theory of Operation	Section E
General Description	E-2
Input Power Circuit:
Input Voltage, Contactor, Reconnect Panel, Pilot Transformer, Control Transformer,
Power Factor Capacitors, and Main Transformer	E-2
Output Rectification and Feedback Control	E-3
High Voltage/High Frequency Circuit	E-4
DC Welding Output	E-5
AC Welding Output	E-6
SCR Operation	E-7
Protective Circuits	E-8
Thermal Protection	E-8
Overload Protection	E-8

FIGURE E.1 – SQUARE WAVE TIG BLOCK LOGIC DIAGRAM

HIGH FREQUENCY SPARK

ELECTRODE SENSE

PANEL	UPPER		LOWER	DISPLAY	STATUS
	CONTROL	CONTROL
SWITCHES				BOARD	BOARD
	PANEL		PANEL

			ELECTRODE		SCR GATE COMMANDS
HIGH VOLTAGE	115VAC		SENSE		15VDC
TRANSFORMER	REMOTE
CIRCUIT		FEED - THRU		CONTROL		POWER
	RECEPTACLE
		BOARD	TRIGGER	BOARD		BOARD
GAS/WATER			REMOTE		INTERLOCK
SOLENOIDS	115VAC		COMMANDS
					HI-FREQ/ WATER/GAS
	INTERLOCK				COMMANDS
			INTERLOCK
			115VAC -HI-FREQ AND GAS/WATER
	FANS 115VAC	115VAC				SNUBBER
	RECEPTACLE	CONTROL TRANSFORMER				BOARD
			115VAC

INPUT	R		AC	DC-
CONTACTOR
	E
					C
	C
			AC	DC+	H
	O				O
	N				K
		POWER			E	BY-PASS
	N						WORK
	E	FACTOR				BOARDS
		CAPACITORS	POLARITY
	C
	T		SWITCH
						SHUNT
	START/	MAIN					ELECTRODE
	STOP
		TRANSFORMER
							HI-FREQ
	PILOT						TRANSFORMER
	TRANSFORMER

SQUARE WAVE TIG 355