engineering

Generator (circuit theory)

Generator (circuit theory) is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Generator (circuit theory) rather than just read about it. In short: A generator in electrical circuit theory is one of two ideal elements: an ideal voltage source, or an ideal current source. These are two of the fundamental elements in circuit theory.

Key takeaways

Generator (circuit theory) belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Generator (circuit theory) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Generator (circuit theory) from memory before moving on to harder problems.

Reference excerpt

A generator in electrical circuit theory is one of two ideal elements: an ideal voltage source, or an ideal current source. These are two of the fundamental elements in circuit theory. Real electrical generators are most commonly modelled as a non-ideal source consisting of a combination of an ideal source and a resistor. Voltage generators are modelled as an ideal voltage source in series with a resistor. Current generators are modelled as an ideal current source in parallel with a resistor. The resistor is referred to as the internal resistance of the source. Real world equipment may not perfectly follow these models, especially at extremes of loading (both high and low), but for most purposes, they suffice. The two models of non-ideal generators are interchangeable; either can be used for any given generator. Thévenin's theorem allows a non-ideal current source model to be converted to a non-ideal voltage source model and Norton's theorem allows a non-ideal voltage source model to be converted to a non-ideal current source model. Both models are equally valid, but the voltage source model is more applicable when the internal resistance is low (that is, much lower than the load impedance), and the current source model is more applicable when the internal resistance is high (compared to the load).

Symbols

Symbols commonly used for ideal sources are shown in the figure. Symbols do vary from region to region and time period to time period. Another common symbol for a current source is two interlocking circles.

Dependent sources A dependent source is one in which the voltage or current of the source output is dependent on another voltage or current elsewhere in the circuit. There are thus four possible types: current-dependent voltage source, voltage-dependent voltage source, current-dependent current source, and voltage-dependent current source. Non-ideal dependent sources can be modelled with the addition of an impedance in the same way as non-dependent sources. These elements are widely used to model the function of two-port networks; one generator is needed for each port, and it is dependent on either voltage or current at the other port. The models are an example of black box modelling; that is, they are quite unrelated to what is physically inside the device but correctly model the device's function. There are a number of these two-port models, differing only in the type of generator required to represent them. This kind of model is particularly useful for modelling the behaviour of transistors.

The model used to represent h-parameters is shown in the figure. h-parameters are frequently used in transistor data sheets to specify the device. The h-parameters are defined as the matrix

[ V 1 I 2 ] = [ h 11 h 12 h 21 h 22 ] [ I 1 V 2 ] {\displaystyle {\begin{bmatrix}V_{1}\\I_{2}\end{bmatrix}}={\begin{bmatrix}h_{11}&h_{12}\\h_{21}&h_{22}\end{bmatrix}}{\begin{bmatrix}I_{1}\\V_{2}\end{bmatrix}}}

where the voltage and current variables are as shown in the figure. The circuit model using dependent generators is just an alternative way of representing this matrix.

References

Illustrations

Worked examples

Example 1 — a first encounter with Generator (circuit theory)

Start with the simplest possible case. Write down what Generator (circuit theory) claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Generator (circuit theory) before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Generator (circuit theory) ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Generator (circuit theory)

In research: Generator (circuit theory) appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Generator (circuit theory) in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Generator (circuit theory) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Circuit theorems, so understanding it makes those chapters shorter.
In everyday life: Look for Generator (circuit theory) outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Generator (circuit theory) in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Generator (circuit theory) means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Generator (circuit theory) out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Generator (circuit theory) in simple terms?

A generator in electrical circuit theory is one of two ideal elements: an ideal voltage source, or an ideal current source. These are two of the fundamental elements in circuit theory.

Why does Generator (circuit theory) matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Generator (circuit theory)?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Generator (circuit theory).