Voltage Source and Current Source

Voltage Source:A device which can produce a continuous force to move the electrons (or, continuous voltage) through the wire connected into the two terminals of the device is called a Voltage Source. There are two types of the Voltage Source which are:

Direct Voltage Source:

A device which produces a continuous direct voltage output is called a Direct Voltage Source. For example: Cells , Battery , DC Generator.


Suggested Readings:
Electromotive force (EMF)
Basics Of Electric Current
Body Or Chassis Ground in Electronic Circuits

A direct voltage is the kind of voltage whose polarity remains the same. Direct Voltage causes the current to move only in one direction continuously.
 

Alternating Voltage Source:

A device which produces a alternating direct voltage output is called a Alternating Voltage Source. For example: AC Generator , DC to AC converter etc.

A alternating voltage is the kind of voltage whose polarity is reversed periodically. Alternating Voltage causes the current to move in one direction for a period and then in another direction for another period.
 

Ideal Voltage Source:

An Ideal Voltage source is a kind of Voltage source whose internal resistance is zero! Such that the supplied voltage does not changes even if the external load resistance is changes.
Anatomy of a Virtually Ideal (Constant) Voltage Source:

A Voltage source which have zero internal resistance or impedance is called an Ideal or Constant voltage source!

But practically it is not possible. No matter how much efforts are made the voltage source still have a small internal resistance , But a voltage source can be converted into a Virtually Constant Voltage Source by changing the internal materials used in a cell or voltage source such that the internal resistance of the source is minimized.

A practical virtual constant voltage source haves a very low internal impedance (let it be 0.005 ohm or 5 mili Ohm in this case) and the actual circuit diagram of a voltage source looks like:


Current Source:

A current source is a device which provides the regular flow or electrons or current on a circuit.

A current source is a type of voltage source which have enough EMF and surplus electrons so as to produce the flow of electrons.
 

Direct Current Source:

The current source made of a Direct Voltage Source is called Direct Current Source.
 

Alternating Current Source:

The current source made of a Alternating Voltage Source is called Alternating Current Source.
 

Ideal Current Source:

A current source which provides a constant current without any relation with the voltage supplied to the load is called Ideal Current Source.
Anatomy of a Virtually Ideal (Constant) Current Source:

Practically a Ideal Current source is impossible but a circuit can be configured such that when the voltage across the load is changed the supplied current current varies negligibly. A virtual Constant or Ideal current source can be made by adding a very high internal impedance to a Voltage Source.a shown in the figure below:


Conversion of Voltage Source into Current Source and Vice Versa:

Here in the following constant voltage source:


The Internal resistance of the voltage source =

The Load resistance =

The Open Voltage across the load resistance = V =

And the Short Current across the load resistance = I Short =

Now we need to convert the above Constant voltage current source into a Constant Current Source with Following anatomy:


  As we can see in the above constant current source:

the Open Voltage = V =

and also the short current = I Short =

Thus the Open Voltage and Short Current in both circuits is same , thus both circuits are electrically equivalent.

Hence , To convert a Constant Voltage Source into a Constant Current Source we need to follow the following steps.

  1. Find the Internal resistance of the Constant Voltage source and place it in parallel with the Voltage source to convert it into a Constant Current Source.
  2. Find the Current flowing through the Load in a Voltage source with the Load resistance being short (I = V / R_i) and the Current Provided by the converted constant current source is the same I.

We can also convert a Constant Current Source into a Constant Voltage Source by following Method:
  1. Find the resistance parallel of the Constant current source and place it in series with the current source to convert it into a Constant Voltage Source.
  2. Find the Open Voltage of the current source ( V = I * R_i) and the voltage provided by the constant voltage source will be the same V.

No comments