Thevenin's theorem explains how to simplify a complex scheme. It states that any linear chain with only voltage sources, current sources and resistors can be simplified to a voltage source with a series resistor.
But what does it really mean?
Sometimes a picture says more than a thousand words, so here are two pictures to explain what all this theorem Thevenin.
This scheme...
... It can be represented by this simple scheme
How to use the Thevenin theorem?
To move from a complex scheme to its simple Thevenin equivalent, we must:
- Calculate equivalent voltage between terminals AB open circuit
- Calculate the equivalent resistance between terminals AB, when all current sources are opened and closed all voltage sources
Finding the equivalent stress
First, we find the equivalent stress.
We see that R4 forms a voltage divider together with R3 and R2. Since R4 = R2 + R3, the voltage will be divided in half at the right side of R4.
Since A to anything not connected, no current will flow through R1, and therefore, no voltage drop will occur across R1. Thus at terminal A will be 7.5 V.
Finding the equivalent resistance
Then let's find the equivalent resistance.
First, we short-circuit the voltage source. This puts R4 in parallel with R2 + R3. We expect equivalent and R4 (R2 + R3) and obtain 1 kW. Connected in series with R1 (also 1 kW), and obtain the total resistance of 2 ohms.
We obtain the Thevenin equivalent circuit of the following:
Why use the Thevenin equivalent circuit?
Thevenin's theorem is really useful to perform calculations with chains. If you have a complicated scheme, you can simplify it and significantly simplify the calculations.
But I must admit that I do not remember to have ever applied it :) Maybe it's my omission?
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