What is a Thévenin equivalent?

A simplified model of a linear network, viewed from two terminals, consisting of an ideal voltage source $V_{th}$ in series with a resistance $R_{th}$.

What does $V_{th}$ represent?

The open-circuit voltage measured across the network's output terminals A–B when no external load is connected.

How is $R_{th}$ defined using independent ideal sources?

It is the resistance looking into the output terminals after setting independent voltage sources to zero (short circuits) and independent current sources to zero (open circuits).

What is the short-circuit current of a Thévenin equivalent?

It is $I_{sc}=V_{th}/R_{th}$, from Ohm's law for the voltage source and its series resistance.

What does the Thévenin model preserve?

It preserves the voltage-current behavior observed at the output terminals by an external load, but not necessarily the original circuit's internal details or power dissipation.

Electrical engineeringLesson 3 of 4 in the course Circuit laws

Thévenin Equivalents: Calculation, Norton Conversion, and AC Limits

5 flashcards · 5 quiz questions · 5 match pairs · 3 fill-in sentences · English

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Summary

Thévenin's theorem simplifies a linear circuit by replacing the network seen from two terminals with one voltage source in series with one resistance or impedance. This lesson introduces the equivalent circuit and explains why it is useful.

A linear network containing sources and resistances can be represented, as viewed from a pair of terminals A–B, by a single ideal voltage source $V_{th}$ in series with a resistance $R_{th}$ . The pair of values is called the network's Thévenin equivalent.

All flashcards

What is a Thévenin equivalent?: A simplified model of a linear network, viewed from two terminals, consisting of an ideal voltage source $V_{th}$ in series with a resistance $R_{th}$ .
What does $V_{th}$ represent?: The open-circuit voltage measured across the network's output terminals A–B when no external load is connected.
How is $R_{th}$ defined using independent ideal sources?: It is the resistance looking into the output terminals after setting independent voltage sources to zero (short circuits) and independent current sources to zero (open circuits).
What is the short-circuit current of a Thévenin equivalent?: It is $I_{sc}=V_{th}/R_{th}$ , from Ohm's law for the voltage source and its series resistance.
What does the Thévenin model preserve?: It preserves the voltage-current behavior observed at the output terminals by an external load, but not necessarily the original circuit's internal details or power dissipation.

Quiz questions

What is the standard form of a Thévenin equivalent for a resistive network?Answer: An ideal voltage source in series with a resistance.
When finding terminal resistance in a circuit with dependent sources, how should those sources be treated?Answer: Leave them active and apply a test voltage or current at the terminals.
How is the Norton current related to the Thévenin voltage and resistance?Answer: $I_{no}=V_{th}/R_{th}$
In frequency-domain AC analysis, what replaces resistance in the Thévenin model?Answer: Impedance, which can include reactive effects.
What does Thévenin equivalence imply about power dissipated inside the original network?Answer: It need not equal the internal power dissipated by the equivalent circuit.

Based on the Wikipedia article Thévenin's theorem, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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