When a network element or circuit element has the ability to deliver electrical energy or to produce power gain in the circuit, then the element is called an active element.
In other words, a circuit element for which the slope of its characteristics curve at any point is negative then the element is called an active element.
Active Elements are the network elements that deliver power to other elements present in an electric circuit. So, active elements are also called as sources of voltage or current type.
We can classify these sources into the following two categories:
As the name suggests, independent sources produce fixed values of voltage or current and these are not dependent on any other parameter.
Independent sources can be further divided into the following two categories:
Independent ideal voltage source and its V-I characteristics are shown in the following figure.
Independent practical voltage source and its V-I characteristics are shown in the following figure.
Independent ideal current source and its V-I characteristics are shown in the following figure.
Independent practical current source and its V-I characteristics are shown in the following figure.
A dependent voltage source produces a voltage across its two terminals. The amount of this voltage is dependent on some other voltage or current.
Hence, dependent voltage sources can be further classified into the following two categories:
Dependent voltage sources are represented with the signs ‘+’ and ‘-’ inside a diamond shape. The magnitude of the voltage source can be represented outside the diamond shape.
A dependent current source produces a current. The amount of this current is dependent on some other voltage or current. Hence, dependent current sources can be further classified into the following two categories:
Dependent current sources are represented with an arrow inside a diamond shape. The magnitude of the current source can be represented outside the diamond shape.
We can observe these dependent or controlled sources in equivalent models of transistors.
The current I flowing through the 7Ω resistor between P and Q (rounded off to one decimal place) is ______ A
We know that there are two practical sources, namely, voltage source and current source. We can transform (convert) one source into the other based on the requirement, while solving network problems.
The technique of transforming one source into the other is called as source transformation technique. Following are the two possible source transformations:
The transformation of practical voltage source into a practical current source is shown in the following figure:
Practical voltage source consists of a voltage source (VS) in series with a resistor (RS). This can be converted into a practical current source as shown in the figure. It consists of a current source (IS) in parallel with a resistor (RS).
The value of IS will be equal to the ratio of VS and RS. Mathematically, it can be represented as
The transformation of practical current source into a practical voltage source is shown in the following figure:
Some active elements are different types of transistors, generators, batteries , independent sources, Op Amps,etc
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1. What are independent sources in electrical engineering? |
2. Can you explain what dependent sources are in network theory? |
3. How can the source transformation technique be used in electrical engineering? |
4. How can a practical voltage source be transformed into a practical current source? |
5. How can a practical current source be transformed into a practical voltage source? |
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