Lincoln Electric SVM152-A service manual Switch Board Main Transformer, Return

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E-3		THEORY OF OPERATION	E-3
	FIGURE E.3 – SWITCH BOARD & MAIN TRANSFORMER
		Main Switch Board	To Control
			Board
			Feedback Current
	Input		Positive
Input switch		Primary	Output
& 100A Breaker	Rectifier		Terminal
		Current

Sensor

Return

Return

Reconnect

Switch

Fan

115VAC Fan Supply

Auxiliary

115VAC, 42VAC Transformer 24VAC

ControlFan

Primary

Current

Sensor

Primary Current Feedback

Input Relay Control

Soft Start Control

V/F Capacitor Feedback (2)

rive S IGBT D

ignal

Choke	Negative
	Output
	Terminal
SenseVoltage Output

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	Machine Control Supply
	+15VDC, -15VDC, +6VDC
	Power
	Board SPI Supply +15VDC +5VDC		Control Board
28VAC	40VDC
14 Pin	RS232 Supply +5VDC
Amphenol
		SPI Communications		& +15VDC, +5VDC Supply
	Solenoid Supply
	40VDC	Remote	Mode	Status	Display
		Board	Panel	Panel	Panel
6 Pin	Remote Control & Trigger
Amphenol

Optional Solenoid

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SWITCH BOARD &

MAIN TRANSFORMER

There is one switch board in the Invertec V350-Pro. This board incorporates two pairs of input capacitors, two insulated gate bipolar transistor (IGBT) switching circuits, a fan motor drive circuit, and a voltage/fre- quency capacitor feedback circuit. The two capaci- tors in a pair are always in series with each other. When the reconnect switch is in the lower voltage position the capacitor pairs are in parallel . Thus two series capacitors in parallel with two series capacitors. When the reconnect switch is in the high voltage posi- tion the two capacitor pairs are in series. Thus four capacitors in series. This is required to accommodate the higher input voltages.

When the input capacitors are fully charged they act as power supplies for the IGBT switching circuits. When welding output is required the Insulated Gate Bipolar Transistors switch the DC power from the input capacitors, "on and off" thus supplying a pulsed DC current to the main transformer primary windings. See IGBT Operation Discussion and Diagrams in this section. Each IGBT switching circuit feeds current to a separate, oppositely wound primary winding in the main transformer. The reverse directions of current

flow through the main transformer primaries and the offset timing of the IGBT switching circuits induce an AC square wave output signal at the secondary of the main transformer. The two current transformers (CT) located on the switch board monitor these primary currents. If the primary currents become abnormally high the control board will shut off the IGBTs, thus dis- abling the machine output. The DC current flow through each primary winding is clamped back to each respective input capacitor when the IGBTs are turned off. This is needed due to the inductance of the transformer primary winding. The firing of the two switch boards occurs during halves of a 50 microsec- ond interval, creating a constant 20 KHZ output. In some low open circuit Tig modes the firing frequency is reduced to 5KHZ.

The Invertec V350-Pro has a F.A.N. fan as needed cir- cuit. The fan operates when the welding output ter- minals are energized or when a thermal over tempera- ture condition exists. Once the fan is activated it will remain on for a minimum of five minutes. The fan dri- ver circuit is housed on the switch board but it is acti- vated from a control board signal.

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

V350-PRO