Lincoln Electric SVM188-A Firing CIRCUIT, Control CIR- Cuit and Rectification, Firing Board

E-3	THEORY OF OPERATION	E-3
	FIGURE E.2 - FIRING BOARD,CONTROL BOARD AND RECTIFICATION

Return to Section TOC

Return to Section TOC

CONTROL	POWER
TRANSFORMER	SWITCH
115VAC
	•
Pilot
Light
w
•	CR2
Secondary
Thermostat
Primary
Theromstat
1CR Coil
	R
	E
	C
	O
	N
	N
	E
	C
	T

CONTACTOR

CR1

							TERMINAL
							STRIP 1
								OUTPUT
FAULT PROTECTION								CONTROL
								SWITCH
							OUTPUT
32VAC						OUTPUT	CONTROL
32VAC				FIRING		CONTROL SIGNAL
32VAC				BOARD
				G	S
14-pin		115VAC	Fan	A	I
				T	G
Amphenol		Receptacle	Motor	E	N
					A
					L
T		115VAC					CONTROL
	S
R		•					BOARD		MODE
	T
E			OUTPUT						SWITCH
I	I
M	R
N	P	TERMINAL
AL	2
			SWITCH				F
42VAC		115VAC					E
							E
MAIN							D
							B
TRANSFORMER							A
							C		POSITIVE
							K
									TERMINAL
							SHUNT	F
								E
								E
							LATCHING	D
							RESISTOR	B
				SCR BRIDGE				A
								C	NEGATIVE
						CHOKE		K	TERMINAL

Return to Section TOC

Section TOC

Return to Master TOC

Return to Master TOC

Return to Master TOC

Master TOC

FIRING CIRCUIT, CONTROL CIR- CUIT AND RECTIFICATION

RECTIFICATION

The “neutrals” of the welding secondary windings in the main transformer are connected together, and the six starts are connected to the six Silicon Controlled Rectifier (SCR) assemblies to form a six-phase output. This six-phase AC output from the main transformer secondary is rectified and controlled by the SCR bridge.

FIRING BOARD

The firing board is powered by the three-phase 32vac transformer windings. Each phase provides two firing pulses, one for each of the two SCRs controlled by that phase. When a gate firing enable*(trigger) signal is received, the firing circuit supplies the proper amount of energy to the gates of the power SCRs. When this gate firing signal is applied at the correct time, the SCR will turn ON. The amount of ON time versus OFF time determines the output of the machine. See SCR Operation. At the same time the latching resistor is connected across the machine’s output circuit. The latching resistor provides a pre-load for the SCR bridge so the SCR’s will stay activated providing open circuit voltage (OCV).

CONTROL BOARD

The control board receives current feedback informa- tion from the shunt and voltage feedback information from the choke and welding output terminals. This feedback information is processed on the control board. The control board compares the commands of the mode switch, the output control potentiometer (or remote control device) and the arc force control with the feedback information and sends the appropriate output control signal to the firing board. In the event of a “fault condition,” the control board de-activates the fault relay (CR2). See Protective Devices and Shut Down Circuits.

An output choke is connected between the neutral con- nection of the main transformer secondaries and the negative output terminal. This large inductor stores energy, and provides current filtering for the welding output of the DC-600.

*Triggering is accomplished by a connection of lead #2 & #4 by way of the Output Terminal Switch or by a remote signal from a wire feeder. The 2 to 4 closure is indicated by LED10 on the firing Board and LED 6 on the Control Board.

Return to

Return to

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

DC-600