What is a Source in Electrical Engineering?
A Source in Electrical Engineering is a device or a system that converts any form of energy such as mechanical energy, chemical energy, thermal energy, etc into Electrical Energy. In other words, a source is a device or system that generates energy that powers the electric circuit. The sources are the starting point of an electrical system that supplies the necessary energy to power the electrical components.
Type of Sources
There are generally two types of sources: voltage sources and current sources.
What is a Voltage Source?
A voltage source in an electric circuit is a two-terminal device or component that provides electrical energy by maintaining a specific potential difference across its terminals.
What is the Ideal Voltage Source?
An Ideal Voltage source is also a two-terminal device or component that provides electrical energy to an electric circuit. However, the potential difference across its terminals is always constant regardless of load. Which means that it has zero internal resistance and infinite current-supplying capabilities.
Since an ideal voltage source has zero internal resistance there is no voltage drop within the source itself regardless of the current flowing through the circuit. These zero internal resistances and zero voltage drop make it capable of maintaining a constant potential difference across its terminals.
Also, due to constant potential difference, the ideal voltage source can supply an infinite amount of current. Therefore, a short circuit in an ideal voltage source cannot affect it.
The ideal voltage source is a complete theoretical concept and practically it is impossible to obtain an ideal voltage source. It is used theoretically to make a circuit analysis easy and understandable.
The symbolic representation of an Ideal Voltage source is given below:
Characteristics of Ideal Voltage Source
The characteristics of an Ideal Voltage source is the relationship between voltage across its terminals and current drawn by the circuit.
From the above figure, the X-axis shows current and Y-axis shows voltage. As you can see, the voltage is always constant even if the current is increasing. Which depicts that the source is supplying constant voltage.
Differences Between Ideal and Practical Voltage Sources
| Aspect | Ideal Voltage Source | Practical Voltage Source |
| Definition | Maintains a constant voltage regardless of current drawn. | Provides nearly constant voltage but is affected by internal resistance. |
| Internal Resistance | Zero. | Small, non-zero resistance in series with the source. |
| Behaviour with Load | Voltage remains fixed regardless of load changes. | Voltage decreases as load current increases. |
| Current Supply | Can provide infinite current. | Limited by the internal resistance and source capacity. |
| Voltage Limit | Voltage does not vary under any condition. | Voltage output reduces under heavy load due to internal resistance. |
| Example | A 12V ideal source always provides exactly 12V, irrespective of load. | A 12V car battery may drop to 11.8V when powering high loads. |
What is a Current Source?
A current source in an electric circuit is a two-terminal device or component that provides a specific current regardless of load or voltage across its terminals.
What is the Ideal Current Source?
An Ideal Current source is also a two-terminal device or component that provides current to an electric circuit. However, the current it delivers is always constant regardless of load or voltage across its terminals.
An ideal current source has infinite internal resistance and due to this, there is no chance of any leakage current coming back to the source itself. This makes it capable to maintain and supply a constant magnitude of current to the load.
The ideal current source is a complete theoretical concept and practically it is impossible to obtain an ideal current source with infinite internal resistance. It is used theoretically to make a circuit analysis easy and understandable.
The symbolic representation of an Ideal Current source is given below:
Characteristics of Ideal Current Source
The characteristics of an Ideal Current source is the relationship between the magnitude of current supplied by the source and voltage across its terminals.
From the above figure, the X-axis shows the voltage across the terminals of a current source and Y-axis shows the current supplied by the source. As you can see, the current is always constant even if the voltage is increasing. Which depicts that the current source is supplying constant current.
Differences Between Ideal and Practical Current Sources
| Aspect | Ideal Current Source | Practical Current Source |
| Definition | Maintains a constant current regardless of voltage across terminals. | Provides nearly constant current but is affected by internal resistance. |
| Internal Resistance | Infinite. | Large but finite resistance in parallel with the source. |
| Behaviour with Load | Current remains fixed regardless of load or terminal voltage changes. | Current may decrease slightly with changes in load resistance or voltage. |
| Voltage Supply | Can supply infinite voltage to maintain constant current. | Limited by the source’s maximum voltage capability. |
| Current Limit | Current does not vary under any condition. | Current may vary due to practical limitations like internal resistance. |
| Example | A 5A ideal source delivers 5A regardless of load resistance. | A constant current driver may deliver approximately 5A but varies slightly. |