Lincoln Electric SVM101-B Precharge & Protection Circuits, Return to Return to Section TOC

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E-3	THEORY OF OPERATION	E-3
	FIGURE E-3 ---PRECHARGE & PROTECTION CIRCUITS

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1

2

3

FAN

LINE

SWITCH

3A

AUXILIARY

TRANSFORMER

TO

WIREFEEDER

POWER SWITCH SECTIONS 20KHZ

LEFT SWITCH BOARD

FET MODULES

			CAP
			FET MODULES		CURRENT
1ø OR 3ø DETETCTION (H5)
					TRANSFORMER
	PRE-CHARGE
INPUT	DRIVER
RECTIFIER	BOARD				CONTROL
	CR1
					BOARD
AC1		PROTECTION
	PULSE
AC2		BOARD			Y-Y FEEDBACK
	TRAIN
AC3
	CR2
A-LEAD
24VDC	PRE-CHARGE
		RIGHT SWITCH BOARD
18VAC	2ND STEP PWM		FET MODULES
	POWERBOARD		CAP
24VAC
	<1 VDC		FET MODULES
	LOCAL	METER	MODE	POT	POT
	REMOTE
	1ST STEP PWM VOLTAGE
	15VDC-CONTROL BOARD FUNCTION VOLTAGE
	24VAC-THERMOSTATS-GUN TRIGGERING

MAIN	CHOKE	RECTIFIER
TRANSFORMER
		HEATSINK
TOP
		1 DIODE

5 DIODES

BOTTOM

5 DIODES

TOP

1 DIODE

CHOKE

VOLTAGE FEEDBACK

CURRENT FEEDBACK-PROTECTION

CHOKE

SHUNT

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PRECHARGE & PROTECTION CIRCUITS

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The DC voltage from the Input Rectifier is applied to the Driver Board to begin charging the Switch Board capacitors at a slow rate. When the pre-charge level is achieved, the input relays close, applying the full DC voltage to the capacitors. Depending on the Code Number of the machine, there will be either two or four relays and they may or may not be mounted on the Driver Board.

The Driver Board is also responsible for gating the Field Effect Transistors (FETs) on the Switch Boards, as directed by the pulse width modulated (PWM) signal from the Control Board.

The Protection Board monitors the capacitors for prop- er balance and voltage level. If an imbalance or over- voltage condition is detected, the Protection Circuit will de-energize the relays, removing the power from the switch circuits. The machine output will also be dis- abled.

Another function of the Protection Board is to detect whether the input voltage is single phase or three phase and pass that information to the Control Board. The maximum output of the machine will be limited to approximately 250 amps with single phase input and 360 amps with 3 phase input.

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NOTE: Unshaded areas of block logic diagram are the subject of discussion

V300-I