Source of Electrical Energy

There are two types of sources of electrical energy
  1. Ideal Voltage Source
  2. Ideal Current Source

Ideal Voltage Source

An ideal voltage source is a two terminal element which maintains a terminal voltage regardless of the value of the current through its terminals. An ideal voltage source can maintain the fixed voltage independent of the load resistance. The internal resistance of an ideal voltage source is equal to zero. ideal voltage source Although ideal sources do not exist in reality so in a practical voltage source the voltage across the terminals of the source keeps falling as the current through it increases.

This behavior can be explained by putting a resistance in series with an ideal voltage source as shown in figure below. practical voltage source Then the terminal voltage V as Examples of voltage sources – Batteries and Electrical Generators are normally used as voltage sources.

Ideal Current Source

An ideal current source is a two terminal element which maintains a current flowing through its terminals regardless of the value of the terminal voltage. The internal resistance of ideal current source is infinite. ideal current source In a practical current source the current through the source decreases as the voltage across it increases, this behavior can be explained by putting a resistance in parallel with the terminals of the current source as shown in the figure. practical current source Then the terminal current is given by  Examples of current sources- Most of the semiconductor devices like transistor etc. are treated as current sources.

Dependent Energy Sources

The two types of sources that we have discussed up to now are called independent sources because the value of the source quantity is not affected in any way by activities in the remainder of the circuit. In dependent sources the source quantity is determined by a voltage or current existing some other location. dependent energy source

Electrical Source Transformation

A current source is dual form of a voltage source and a voltage source is dual form of a current source. A voltage source can be converted into equivalent current source and a current source can also be converted into equivalent voltage source. We can understand the conversion process as

Voltage Source to Current Source Conversion

Assume a voltage source with terminal voltage V and the internal resistance r. Now according to the Ohm’s law current through the source can be calculated as  This current is supplied by the equivalent current source and same resistance r will be connected across the source. Voltage source to current source conversion is shown in the following figure. voltage to current source transformation

Current Source to Voltage Source Conversion

Similarly assume a current source with value I and internal resistance r. Now according to the Ohm’s law the voltage across the source can be calculated as  current to voltage source transformation

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