What is an Electrical Source

8/13/2019 What is an Electrical Source

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What Is An Electrical Source?

You probably suspect an

electrical source has to besomething that gives you a

voltage or a current, and

you would be correct.


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Why Are Sources Important?

Electrical sources, in practice, includethings like:

batteries,

the ever-present wall plug,

power supplies (like those little things you

use with your calculator and other things) and many other kinds of electrical devices

that deliver electrical energy.


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What Is An Ideal Voltage Source?

A voltage source that can maintain a

constant voltage - no matter what you do

to it, like drawing a lot of current, or putting

it in a situation where current flows

through it - is an ideal voltage source.


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Ideal Voltage Source

An ideal voltage source is a voltagesource that maintains the samevoltage across the source's terminalsno matter what current is drawn fromthe terminals of the source or whatcurrent flows into the terminals.


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The voltage across the terminals isdenoted as Vt.

The load current flowing from thesource to a load (presumably a load

is attached when the source is in acircuit) is denoted as IL.

With those definitions, here is thesource symbol. It's just a circle withpolarity indicated.


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Vt = constant, no matter

what the load current is.


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Direct Voltage Source:

Alternating Voltage Source:

Ideal Voltage Source:


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Direct Voltage Source:

A device which produces a continuous direct voltage

output is called a Direct Voltage Source. For example:

Cells , Battery , DC Generator.

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.


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Alternating Voltage Source:

A device which produces a alternating direct voltageoutput is called a Alternating Voltage Source. Forexample: AC Generator , DC to AC converter etc.

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


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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 evenif the external load resistance is changes.


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Current Source:

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

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

There is a special circuit symbol for an idealcurrent source. See below.


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Symbol and Graph


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IL = constant, no matter what the terminal

voltage is.

The plot of load current against terminal

voltage is similar to the plot for an ideal

voltage source, but voltage and current

are interchanged. Here is the plot.


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Types of current sources:

Direct Current Source:

The current source made of a Direct Voltage Source iscalled 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 currentwithout any relation with the voltage supplied to the loadis called Ideal Current Source.


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Conversion of Voltage Source into

Current Source and Vice Versa:

The Internal resistance of the voltage source =Latex formula

The Load resistance = Latex formula

The Open Voltage across the load resistance =V = Latex formula

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

Now we need to convert the above Constant

voltage current source into a Constant CurrentSource with Following anatomy:


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As we can see in the above constant current source:

the Open Voltage = V = Latex formula

and also the short current = I Short = Latex formula

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


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Hence , To convert a Constant Voltage Sourceinto a Constant Current Source we need to

follow the following steps.

Find the Internal resistance of the ConstantVoltage source and place it in parallel with the

Voltage source to convert it into a ConstantCurrent Source.

Find the Current flowing through the Load in aVoltage source with the Load resistance being

short (I = V / R_i) and the Current Provided bythe converted constant current source is thesame I.


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We can also convert a Constant Current Sourceinto a Constant Voltage Source by followingMethod:

Find the resistance parallel of the Constantcurrent source and place it in series with thecurrent source to convert it into a Constant

Voltage Source. Find the Open Voltage of the current source ( V

= I * R_i) and the voltage provided by theconstant voltage source will be the same V.

What is an Electrical Source

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