You may come across a number of voltage sources and also current sources in our day to day life.
Batteries, DC generator or alternator etc, each one is quite normal instances of voltage sources.
Additionally, there are some current resources experienced in our everyday routine, for example solar cells, metadyne generator etc.
The methods could be classified into two distinct types - independent source and dependent source.
Independent Voltage Source
Output from an independent source will not rely on the voltage or current of some other element of the system. When terminal voltage of a voltage source is not influenced by the current or voltage of some other section of the system, then the source is stated to be an independent voltage source.
This kind of sources could be understood as constant source or time variant source. When terminal voltage of an independent source stays consistent all through its functioning time frame, it is known as time-invariant or constant individual voltage source.
Yet again independent voltage source could be time-variant type, in which the output terminal voltage of the source my vary over time. Here, the source terminal voltage doesn't fluctuate with voltage or current variations involving another section of the network however it varies with respect to time.
Independent Current Source
In the same manner, output current of independent current source would not rely on the voltage or current of some other aspect of the system. It is likewise classified as independent time-invariant and time-variant current source.
Symbolic illustrations of independent time-invariant and time-variant voltage and current sources can be visualized in the following table.
Next, let's talk about dependent voltage or current source. It can be understood as the source whose output voltage becomes the function of voltage or current of some other portion of the circuit.
In the same way, dependent current source could be identified as the source whose output current becomes the function of current or voltage of some other elements of the circuit.
We can take an amplifier as an perfect illustration of dependent source in which the output signal depends upon the an external input signal.
Dependent Voltage Source and Dependent Current Source
One can find 4 practical dependent sources as shown in the following explanation:,
- Voltage which depends on another voltage source.
- Current that depends on another voltage source.
- Voltage that depends on another current source.
- Current that depends on another current source.
Dependent voltage and current sources can also be dependent on and therefore time variant or time invariant.
Meaning, when the output voltage or current of a dependent source is changed with respect to time, it is called time invariant dependent current or voltage source. Alternatively, when it functions without varying with time, it is recognized as time variant.
Ideal Voltage Source
In just about every existing voltage source, you can find certain electrical resistance within it. This resistance is referred to as internal resistance of the source. In situations when the source terminal is open circuited, no current moves through it; thus no voltage drop is experienced within the source.
However when we connect a load across the source, current begins moving via the load along with the source itself. As a result of resistance across the voltage source certain voltage drop across the source is developed.
In this situation if we measure the terminal voltage of the source, we may find the voltage level lowered corresponding to a magnitude that's proportional to the internal voltage drop of the source.
Therefore you will always see a change between no-load (while source terminals are not connected to any form of load) and with a load for a given practical voltage source.
Said that, for ideal voltage source this difference is regarded as as zero which means there may not be any drop in its voltage as long as current is flowing through it and this signifies that the internal resistance of a specified ideal source has to be zero.
Therefore from this we are able to deduce that, voltage throughout the source continues to be constant for all magnitudes of load current.
The V-I characteristics of an ideal voltage source is proven in the following illustration:
You may not find any an practical example of ideal voltage source nevertheless a battery source such as from a lead acid battery or a dry cell could be regarded as a good example with a condition where current consumed from it is restricted below a specified level.
Ideal Current Source
Ideal current sources could be considered as sources that offer constant current to the connected
load no matter what their impedance may be. Meaning, regardless of what could be the load impedance; ideal current source will consistently supply an uniform amount of current through it.
Even if the load exhibits limitless impedance or shows an open circuit condition across the ideal current source, it will continue to offer the same magnitude of constant current through it. Therefore obviously as the definition implies it is apparent that this form of current source may be hardly feasible in a practical environment.
Current Source to Voltage Source Conversion
Each and every electrical source will provide the connected load with both current and voltage supplies. This may not be basically feasible to tell apart between the sources of voltage and current.
Any kind of electrical source could be depicted as voltage source and also like a current source. It purely is determined by the working circumstance of the system. In case the load impedance is significantly over the internal impedance of the supply source, then it can be more appropriate to look at the source as a voltage source.
On the other hand if the load impedance is notably below internal impedance of the supply; it would be much better considering the conversion of current source to voltage source, or conversion of voltage source to current source may likewise be achievable.
At this point we are going to explore how you can transform a current source into voltage source and/or the other way round.
Imagine a voltage source without a load connected, and having a terminal voltage or source voltage V and an internal resistance r.
With this situation, it may be possible for us to convert this to an equivalent current source.
For this, initially we must compute the current that could possibly be moving across the source with a condition wherein the terminal A and B of the supply source had been directly touched or short circuited. This would simply result in the ohm's law expression I = V/r.
The result of this formula will gives us the current that will be supplied by the equivalent current source and this current source will possess exactly the same level of resistance hooked up across it.
In the very same manner, a source of current carrying an output I connected to a resistance r could be transformed into an proportionate voltage source through the formula V = Ir, where the resistance r may be assumed to connected in series with the source.
