Energy Sources

ENERGY SOURCES

Energy sources are devices which supply electric energy. It can be classified as

(i) Voltage sources

(ii) Current sources

Voltage Sources

Ideal voltage source

Ideal voltage source is a source which delivers energy with specified terminal voltage, which is independent of the current supplied by the source. For ideal voltage source the internal resistance / impedance is zero. It is shown in figure 1.7 (a).

Practical voltage source

All practical voltage sources fall short of an ideal source and the terminal voltage Hence, a practical source is represented by voltage source in series with an internal resistance Rs or impedance. It is shown in figure 1.7 (b).

Current Sources

Ideal current source

The ideal current source is a source which delivers energy with a specified current which is independent of the voltage at its terminals. The internal impedance (or admittance) of an ideal current source is zero. It is shown in figure 1.8 (a).

Practical current source

Practical current source is represented by the current source I in parallel with internal impedance (or resistance). In a practical current source, current supplied by increase in voltage. It is shown in figure (1.8 (b)).

Dependent Sources

A dependent voltage or current source is one which depends on some other quantity in the circuit which may be either a voltage or a current. Such a source is represented by a diamond shaped symbol.

There are four types of dependent sources.

1. Voltage dependent voltage source

2. Current dependent voltage source

3. Voltage dependent current source

4. Current dependent current source

Figure (1.8 (c)) shows symbolic representation of dependent sources.

(i) Voltage dependent voltage source

(ii) Current dependent voltage source

(iii) Voltage dependent current source

(iv) Current dependent current source

The constants of proportionality are written as a, r, g and β in which ɑ and  β has no units, r has unit of Ω and g has unit of 

Independent sources actually exist as physical entities such as battery, a DC generator and an AC generator etc. But, dependent sources are part of models that are used to represent electrical properties of electronic devices, such as transistors and operational amplifiers.