Lincoln Electric SP-100 service manual Output CONTROL, RECTIFICA- Tion and Voltage Feedback

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THEORY OF OPERATION		E-2
	FIGURE E.2 – Output Circuits

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OUTPUT CONTROL, RECTIFICA- TION AND VOLTAGE FEEDBACK

The AC voltage that is applied to the main transformer primary is controlled at the con- trol board by two SCR’s (Silicon Controlled Rectifiers). The SCR’s are controlled by a pulse signal developed on the control board. The control board compares the commands of the arc voltage control with the voltage feedback signal. The board circuitry then sends a pulse to turn on the SCR’s. In this manner, the voltage applied to the primary of the transformer is varied and controlled. This variable and controlled voltage is

reflected at the transformer secondary wind- ing and is applied to the rectifier diode bridge. This rectified DC voltage is filtered by the output capacitor and choke circuit and is applied to the machine’s output ter- minals.

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

SP-100