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E-7

E-7

THEORY OF OPERATION

FIGURE E.9 – SCR OPERATION

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ANODE

INPUT

CATHODE

OUTPUT

GATE

NOTE: AS THE GATE PULSE IS APPLIED LATER IN THE CYCLE THE SCR OUTPUT IS DECREASED.

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GATE

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SCR OPERATION

A silicon controlled rectifier (SCR) is a three-terminal device used to control rather large currents to a load. An SCR acts very much like a switch. When a gate sig- nal is applied to the SCR, it is turned ON and there is current flow from anode to cathode. In the ON state the SCR acts like a closed switch. When the SCR is turned OFF there is no current flow from anode to cath- ode. Thus, the device acts like an open switch. As the name suggests, the SCR is a rectifier, so it passes cur- rent only during positive half cycles of the AC supply. The positive half cycle is the portion of the sine wave in which the anode of the SCR is more positive than the cathode.

When an AC supply voltage is applied to the SCR, the device spends a certain portion of the AC cycle time in the on state and the remainder of the time in the off state. The amount of time spent in the ON state is con- trolled by the gate.

An SCR is fired by a short burst of current into the gate. This gate pulse must be more positive than the cath- ode voltage. Since there is a standard PN junction between gate and cathode, the voltage between these terminals must be slightly greater than 0.6V. Once the SCR has fired, it is not necessary to continue the flow of gate current. As long as current continues to flow from anode to cathode, the SCR will remain on. When the anode to cathode current drops below a minimum value, called holding current, the SCR will shut off. This normally occurs as the AC supply voltage passes through zero into the negative portion of the sine wave. If the SCR is turned on early in the positive half cycle the conduction time is longer, resulting in greater SCR output. If the gate firing occurs later in the cycle the conduction time is less, resulting in lower SCR output.

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SQUARE WAVE TIG 275

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Lincoln Electric SVM141-A service manual Figure E.9 SCR Operation
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SVM141-A specifications

The Lincoln Electric SVM141-A is a cutting-edge solution designed for operators requiring precision, efficiency, and versatility in their welding applications. This machine is known for its compact form but robust feature set, making it an ideal choice for both professional welders and industrial applications.

One of the standout features of the SVM141-A is its advanced inverter technology. This innovation allows for a stable arc, providing consistent results even under varying conditions. The machine minimizes power consumption, making it energy-efficient without compromising performance. The inverter technology also supports a wider input voltage range, making the SVM141-A suitable for use in diverse environments and job sites.

Another key characteristic is its multi-process capability. The SVM141-A supports MIG, stick, and TIG welding processes, providing flexibility for various welding tasks. This versatility enables operators to tackle different materials, including mild steel, stainless steel, and aluminum, making it a valuable tool for numerous projects.

The user-friendly interface of the SVM141-A includes an intuitive digital display, which allows welders to adjust settings with ease. This feature is crucial for ensuring the right configurations for specific welding tasks, reducing the chances of errors and enhancing the overall finish of welds.

Safety is also a priority with the Lincoln Electric SVM141-A. It comes with built-in safety features such as overheat protection and automatic shutdown, ensuring operator safety and equipment longevity. The machine's lightweight design enhances portability, allowing it to be used in various workspaces with ease.

Durability is another hallmark of the SVM141-A. Constructed with high-quality materials, the machine is designed to withstand the rigors of demanding work environments. This ensures reliability over time, providing consistent performance even under heavy use.

In summary, the Lincoln Electric SVM141-A is a versatile, efficient, and user-friendly welding machine that appeals to a wide range of users. Its advanced inverter technology, multi-process capabilities, safety features, and durable construction make it a strong contender in the welding market, suitable for both professionals and hobbyists alike. Whether it’s for light fabrication, repairs, or industrial welding tasks, the SVM141-A meets diverse needs with precision and reliability.
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