Discover Thevenin's theory

Thevenin's theory
Thevenin's theorem states that any complex network across its load terminals can be replaced by a voltage source with one resistance in series. This theory helps in studying the variation of current in a particular branch when the resistance of the branch varies while the remaining network remains the same.

For example in the design of electrical and electronic circuits.

A more general statement of Thevenin's theory is that any linear active network consisting of an independent or dependent voltage and current source and network elements can be replaced by an equivalent circuit having a voltage source in series with a resistance.

Where the voltage source is the open circuit voltage across the open circuit load terminals and the resistance is the source's internal resistance.

In other words, the current flowing through a resistor connected through any two terminals in the network in an equivalent circuit having an Eth voltage source in series with the resistor Rth. where Eth is the open circuit voltage between the two required terminals called Thevenin voltage and Rth is the equivalent resistance of the network as seen from two ends with all other sources replaced with their internal resistances called Thevenin resistance.



Explanation of Thevenin's theory

Steps to Solve Thevenin's Theorem

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Explanation of Thevenin's theory

Thevenin's statement is explained with the help of the circuit shown below:

Thevenin's-Theorem-figure-1 Let's consider a simple DC circuit as shown in the above figure, where we have to find the load current IL by Thevenin's theorem.

In order to find the equivalent voltage source, r is removed from the circuit as shown in the figure below and V or VTH is calculated.

Thevenin's Theorem Figure 2

So, thevenin theory EQ1

Now, to find the internal resistance of the network (Thevenin resistance or equivalent resistance) in series with the open circuit voltage VOC, also known as Thevenin voltage VTH, the voltage source is removed or we can say that it is disabled by a short circuit (the source has no internal resistance) As shown below:

Thevenin's Theorem Figure 3

Therefore, Thevenin theory EQ2

And therefore,

Thevenin's theorem Figure 4

Equivalent circuit of Thevenin theorem

According to Thevenin statement, the load current is determined by the circuit shown above and the equivalent Thevenin circuit is obtained.

The load current IL is given as:

Thevenen EQ3 Theory

where,

VTH is Thevenin Equivalent Voltage. It is an open circuit voltage across terminal AB known as load terminal

RTH is Thevenin equivalent resistance, as indicated by load stations where all sources are replaced by their internal resistance

L is the load resistance

Steps to Solve Thevenin's Theorem

Step 1 - First of all, remove the load resistance r of the given circuit.

Step 2 - Replace all sources with their internal resistance.

Step 3 - If the sources are perfect, then short the voltage source and open the current source circuit.

Step 4 - Now find the equivalent resistance at the load terminals, known as Thevenin resistance (RTH).

Step 5 - Draw the Thevenin equivalent circuit by connecting the load resistance and then specify the desired response.

This theory is perhaps the most widely used network theory. It is applicable when it is required to determine the current through or voltage across any one element in the network. Thevenin theorem is an easy way to solve a complex network.