Lincoln Electric SP-250 service manual Output Rectification and Feed, Back Control

E-2 THEORY OF OPERATION E-2

to Section TOC	to Master TOC		POWER SUPPLY OPERATION (CONTINUED)
Return	Return			PIEZO	GAS
			LCD	ALARM	SOLENOID
			DISPLAY				WIRE
							DRIVE
							MOTOR
			KEYPAD	CONTROL BOARD
					G		TACH
					A
					T		GUN TRIGGER AND THUMB SWITCH
		LINE	MAIN		E
					S
			TRANSFORMER
		SWITCH			I		FEEDBACK
					G
					N
TOC	TOC				A
					L
			RECONNECT				POSITIVE
Section	Master
							TERMINAL
						C	CHOKE
						A	F
						P	E
to	to					A	E
						C	D
				SCR		I	B
Return	Return
				RECTIFIER		T	A
						O	C
			FAN			R	K
						S	NEGATIVE
			MOTORS				TERMINAL
							SHUNT

Figure E.3 - Output Rectification and Feedback Control

TOC	TOC	OUTPUT RECTIFICATION AND FEED-
Sectionto	Masterto	BACK CONTROL
Return	Return	The AC output from the main transformer secondary
		weld winding is rectified and controlled through the
		SCR rectifier assembly. Output voltage and current
		are sensed at the shunt and output terminals and fed
		back to the control board. The control board compares
		the commands of the keypad (or gun thumb switch)
		with the feedback signals. The appropriate gate firing
		pulses are generated by the control board and applied
		to the SCR rectifier assembly. The control board con-
		trols the firing of the SCRs, thus controlling the output
TOC	TOC	of the machine. See SCR Operation. The control
		board also powers and commands the keypad, the
		LCD Display, the piezo alarm, the gas solenoid and the
Section	Master	wire drive motor.
to	to		NOTE: Unshaded areas of Block Logic
			Diagram are the subject of discussion
Return	Return
			IDEALARC SP-250