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Theory Thevenin and Norton

A circuit or linear network, active and resistive containing one or more sources of voltage or current source can be replaced with a voltage source and a series resistance (Theorem Thevenin) or a current source and a parallel resistance (Theorem Norton). The voltage is referred to as a replacement voltage UT and current source called current source IT penggnati resistannya’re both the same.
Thevenin and Norton’s theory is only applied to the circuit the two terminals, which consists of a resistance element and a constant voltage source.

Thevenin theory
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Figure 4.2 active two-terminal circuit

According to Thevenin, an active two-terminal circuit can be replaced with a voltage source UT and RT resistance is connected in series (Figure 4.3).
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Figure 4.3 Thevenin equivalent circuit

Where UT is an open-circuit voltage of the circuit the two terminals (Uab) and RT is the total resistance seen from ab terminal when the voltage source of the circuit the two terminals short circuited.

Theory Norton
And according to Norton, a circuit with two terminals can be replaced with a constant current source IT and a parallel resistance RT.
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Figure 4.4 Equivalent Circuit Norton

Where IT is a short circuit current that flows when terminals ab short circuited and RT is the total resistance seen from ab terminal when the voltage source of the circuit the two terminals short circuited.

Example 1:
Determine the equivalent circuit thevenin and Norton, of an active two-terminal circuit having two resistors R1 = 10 ohms, R2 = 30 ohm, and Us = 12V, as shown below.
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Solution:
According thevenin, a two-terminal circuit can be replaced with a voltage source UT, the open-circuit voltage at the terminals ab and Resistance RT, connected in series, in which RT is the total resistance when short circuited Us (R1 // R2).
Thevenin equivalent circuit is:
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Where:
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According to Norton, a circuit with two terminals can be replaced with a constant current source IT and a parallel resistance RT. Where IT is a short circuit current that flows when terminals ab short circuited and RT is the total resistance seen from ab terminal when the voltage source of the circuit the two terminals short circuited.

Norton equivalent circuit:
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Where:
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