Difference Between Dependent and Independent Sources

Dependent and independent sources are used very often when designing and analyzing an electrical circuit.

The electrical source is the power source that provides active power to the network. There are two sorts of electrical sources: independent and dependent sources. The terms “independent” and “dependent” refer to whether voltage or current sources are dependent on another source or act independently.

Difference Between Dependent and Independent Sources

Independent source is a source that is not dependent on any other variable in the circuit. They are two-terminal devices with a constant value, which means that the voltage across the two terminals remains constant under all circuit conditions.

Dependent or controlled sources are sources which have an output voltage or current that is not fixed and is dependent on the voltage or current in another section of the circuit. They are components with four terminals.

Independent Voltage and Current Source

The term “independent source” refers to a source that is not dependent on any other variable in the circuit. They are two-terminal devices with a constant value, which means that the voltage across the two terminals remains constant under all circuit conditions.

When the strength of voltage or current is unaffected by changes in the connected network, the source is referred to as an independent voltage or current source. The voltage or current value is fixed in this case and cannot be changed.

Regardless of the other components in the circuit, an ideal independent source maintains the same voltage or current. It has a constant value (DC) or a sinusoidal value (AC). Variations in the connected network have no effect on the strength of voltage or current.

Independent Voltage Source

An independent voltage source has its voltage independent from other values in the circuit. If you have a 5V voltage source then it will supply voltage at 5V to the circuit. It doesn’t matter how much current will be generated in the circuit.

The term “constant source” or “time variant source” can be used to describe this type of source. A time–invariant or constant independent voltage source is one in which the terminal voltage of an independent source remains constant during its operation.

Again, an independent voltage source can be of the time–variant type, with the source’s output terminal voltage changing with time. The source’s terminal voltage does not change with changes in voltage or current in any other portion of the network, but it does fluctuate with time.

Below is the common symbol of an independent voltage source,

There are some main points you need to remember about an independent voltage source:

• It is a two-terminal circuit element and able to generate fixed voltage in the circuit.
• Its voltage value can not be affected by the current flowing through it.
• It is specified independently from other variables in the circuit.

Independent Current Source

An independent current source has its current independent from other values in the circuit. If you have a 5A current source then it will supply current at 5A to the circuit. It doesn’t matter how much voltage will be generated in the circuit.

Below is the common symbol of an independent current source,

There are some main points you need to remember about an independent current source:

• It is a two-terminal circuit element and able to generate fixed current in the circuit.
• Its current value can not be affected by the voltage across it.
• It is specified independently from other variables in the circuit.

Read also : laplace transform

Dependent Voltage and Current Source

Dependent or controlled sources have an output voltage or current that is not fixed and is dependent on the voltage or current in another section of the circuit. They are components with four terminals.

Dependent sources occur when the value of voltage or current varies in the source as a result of a change in the associated network. A diamond shape represents the dependent sources.

A dependent source is one whose value is determined by another circuit variable. The voltage or current values in the circuit are proportional to another voltage or current. Modeling the behavior of amplifiers, for example.

There are two common examples of this dependent source:

1. A bipolar junction transistor can be a dependent current source, with the magnitude of the current delivered into its regulating base terminal determining the magnitude of the current.
2. An operational amplifier is a voltage source whose output is determined by the difference in input voltage between its input terminals.

The dependent sources are further divided into the following categories:

Voltage Controlled Voltage Source (VCVS)

The voltage source is reliant on any element in the circuit in a voltage-controlled voltage source.

In the circuit above we conclude that the value of the dependent voltage source (aV_X) depends on the value of the voltage V_X across the resistor R.

Where a is the constant.

Voltage Controlled Current Source (VCCS)

Just as the name implies, this is a current source (bV_X) which its value is dependent on the voltage V_X in the circuit as shown in figure below:

Where b is a constant.

Current Controlled Voltage Source (CCVS)

The current controlled voltage source is a voltage source whose value is determined by the current in the circuit somewhere.

The voltage source ci_X value is dependent on the current value i_X. With c as a constant.

Current Controlled Current Source (CCCS)

The current controlled current source is a current source with its value determined by other current in the circuit just as shown in figure below.

With d is a constant.

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