Dependent And Independent Sources

Electric circuit: An electric circuit is a closed path comprising of electrons flowing along it from a voltage source or a current source.

Important points: 

1.Source-The point where the electrons enter an electrical circuit.
2.Return- exit point.
3.Load-  The part of an electrical circuit that is between the electrons’ starting point and the point where they return to the source.
4. The electric circuit use alternating current sources.

Electric Circuit

Sources are of two types-  dependent sources and independent sources

1)Dependent source : A dependent source is one whose value depends on some other variable in the circuit. The voltage or current values is proportional to some other voltage or current in the circuit. for example, in modelling the behavior of amplifiers.

Examples:

1)A bipolar junction transistor can be  a dependent current source whose magnitude depends on the magnitude of the current fed into its controlling base terminal.

2)An operational amplifier can be described as a voltage source dependent on the differential input voltage between its input terminals.

Classification:

Dependent sources can be classified as follows:

Voltage-controlled voltage source: The source delivers the voltage as per the voltage of the dependent element. V=avx
Voltage-controlled current source: The source delivers the current as per the voltage of the dependent element. I=bvx
Current-controlled current source: The source delivers the current as per the current of the dependent element. I=cix
Current-controlled voltage source: The source delivers the voltage as per the current of the dependent element. V=Idx

-The proportionality constant between dependent and independent variables is dimensionless if they are both currents (or both voltages).

– A voltage controlled by a current has a proportionality factor expressed in units of resistance (ohm), and this constant is sometimes called “trans-resistance”.

– A current controlled by a voltage has the units of conductance , and is called “trans-conductance”.

-Trans-conductance is a commonly used specification for measuring the performance of field effect transistors and vacuum tubes.

2) Independent sources: Ideal Independent Source maintains same voltage or current regardless of the other elements present in the circuit.Its value is either constant (DC) or sinusoidal (AC). The strength of voltage or current is not changed by any variation in connected network.

Example: a Copper resistance along the circuit

Classification:

1) Ideal Independent Voltage Sources
An ideal independent voltage source is a two-terminal circuit element where the voltage across it
a) is independent of the current through it
b) can be specified independently of any other variable in a circuit.

In a circuit, voltage across elements which are parallel with voltage sources are equal to the voltage of the corresponding voltage sources

2) Ideal Independent Current Sources
In contrast to ideal independent voltage sources, an ideal independent current source is a two-terminal circuit element where the current passing through it
a) is independent of the voltage across it
b) can be specified independently of any other variable in a circuit.