Name: thevenin circuit equivalents
Uploaded: 2024-04-11T12:48:31.000Z
Duration: 1 min 15 s
Channel: JoVE

Thevenin&#39;s theorem states that any linear two-terminal circuit can be replaced by an equivalent circuit with a single voltage source in series with a resistor.
In the absence of load, the voltage across the open terminals will be the Th&#233;venin voltage.
For finding Th&#233;venin resistance, all independent sources are turned off. Then the resistance seen across the terminals is the Th&#233;venin resistance.
If the circuit contains dependent sources, the independent sources are still switched off, but a known test source is applied at the terminals.
From the resulting terminal voltage or current, the Th&#233;venin resistance can be determined.
Finally, the load is connected to the equivalent circuit. The current through the load is calculated using the current divider formula. Using Ohm&#39;s Law, the Th&#233;venin voltage across the load is determined.
A battery can be represented as the Th&#233;venin equivalent circuit. Th&#233;venin voltage is the battery&#39;s open circuit voltage and resistance is its internal resistance.
Knowing the Th&#233;venin parameters, it is easy to calculate the current for various loads without re-examining the entire circuit.

thevinin's theorem

Th&#233;venin's theorem plays a pivotal role in electrical circuit analysis, offering a solution to the challenges posed by variable loads within a circuit. In practical applications, it is common to encounter circuits where certain elements remain fixed while others fluctuate, often referred to as the "load." A typical household electrical outlet serves as a prime example of a variable load, as it can be connected to a variety of appliances, each with its own unique electrical characteristics. Every time a new appliance is plugged in or removed, the entire circuit requires a fresh analysis. Th&#233;venin's theorem provides a technique that replaces the fixed portion of the circuit with an equivalent circuit, thereby simplifying analysis and design.
Th&#233;venin's theorem states that a linear two-terminal circuit can be represented by an equivalent circuit consisting of a voltage source in series with a resistor. This equivalent circuit effectively encapsulates the behavior of the original circuit from an external perspective. Two critical parameters define this Th&#233;venin equivalent circuit: the Th&#233;venin equivalent voltage (VTh), which corresponds to the open-circuit voltage at the terminals, and the Th&#233;venin equivalent resistance (RTh), which represents the input or equivalent resistance at the terminals when all independent sources are deactivated.
To illustrate the concept further, consider two circuits shown in Figure 1 and Figure 2. These circuits are deemed equivalent when they share the same voltage-current relationship at their terminals. When the terminals are left open-circuited, resulting in no current flow, the voltage across the open terminals will be the Th&#233;venin voltage. When all independent sources are turned off. Then the resistance seen across the terminals is the Th&#233;venin resistance.
<img alt="Linear two-terminal circuit diagram; electrical circuit analysis, showing voltage VOC terminals a, b." src="/files/ftp_upload/15053/15053_PT_Figure_1.svg" style="text-align: center; height: 128px;" data-altupdatedat="1761830439000" data-alt="Figure1" />
Figure 1
<img alt="Thevenin equivalent voltage equation VTh=Voc, formula for circuit voltage analysis." src="/files/ftp_upload/15053/15053_PT_Equation_1.svg" style="text-align: center; height: 14px;" data-altupdatedat="1761830439000" data-alt="Equation1" />
<img alt="Linear circuit diagram, independent sources zeroed, finding input resistance Rin across points a, b." src="/files/ftp_upload/15053/15053_PT_Figure_2.svg" style="text-align: center; height: 128px;" data-altupdatedat="1761830439000" data-alt="Figure2" />
Figure 2
<img alt="Thevenin's theorem formula R&#60;sub&#62;Th&#60;/sub&#62;=R&#60;sub&#62;in&#60;/sub&#62;, circuit analysis, electrical engineering." src="/files/ftp_upload/15053/15053_PT_Equation_2.svg" style="text-align: center; height: 14px;" data-altupdatedat="1761830439000" data-alt="Equation2" />
To practically apply this idea and determine the Th&#233;venin resistance, we must consider two scenarios:
CASE 1: In situations where the network contains no dependent sources, all independent sources are deactivated and the input resistance is ascertained, which is the resistance seen between terminals a and b.
CASE 2: When the network incorporates dependent sources, continue to deactivate all independent sources. However, refrain from deactivating dependent sources since they are controlled by circuit variables.
It is worth noting that the value of Th&#233;venin resistance (RTh) can sometimes be negative, signifying that the circuit is supplying power rather than consuming it. This scenario is feasible in circuits with dependent sources.

Thevinin's Theorem

Thevenin&#39;s theorem states that any linear two-terminal circuit can be replaced by an equivalent circuit with a single voltage source in series with a ...

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KEY TERMS AND CONCEPTS

thevenin circuit equivalents

Thevenin circuit equivalents simplify linear two-terminal circuits by replacing the fixed part of a network with one equivalent source and one resistor. This method is useful when a circuit has a fixed section and a load that can change. A household electrical outlet is a familiar example, because different appliances can be plugged in or removed. Each change in load can require a new circuit analysis, so an equivalent circuit makes the work easier.

Thevenin's theorem states that a linear two-terminal circuit can be represented by a voltage source in series with a resistor. From the outside, this equivalent circuit has the same behavior as the original network. Two circuits are considered equivalent when they have the same voltage-current relationship at their terminals. The Thevenin equivalent voltage, VTh, is the open-circuit voltage at the terminals, and the Thevenin equivalent resistance, RTh, is the input resistance seen at the terminals when the independent sources are turned off.

To find the Thevenin resistance, the method depends on the kind of sources in the network. If the circuit has no dependent sources, all independent sources are deactivated and the resistance between terminals a and b is found. If the network includes dependent sources, the independent sources are still turned off, but the dependent sources stay active because they are controlled by circuit variables. In some cases, RTh can be negative. That means the circuit is supplying power instead of consuming it, which can happen in circuits with dependent sources.

Thevenin Circuit Equivalents

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Thevenin circuit equivalents simplify linear two-terminal circuits by replacing the fixed part of a network with one equivalent source and one resistor. This method is useful when a circuit has a fixed section and a load that can change. A household electrical outlet is a familiar example, because different appliances can be plugged in or removed. Each change in load can require a new circuit analysis, so an equivalent circuit makes the work easier. Thevenin's theorem states that a linear...

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key terms and concepts

Learn how Thevenin’s theorem replaces a linear two-terminal circuit with a voltage source and resistor, and how to find VTh and RTh in circuit analysis.

Thevenin Circuit Equivalents | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Thevenin Circuit Equivalents

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