Voltage and Current Source Conversion. 1

Ideal Sources. 2

Real Sources. 2

Real Source (Voltage). 3

Solution. 4

Constant Current Sources. 4

Real Source (Current). 4

Example. 5

Solution. 5

Source Conversion. 6

Converting a Voltage Source to a Current Source. 6

Converting a Current Source to a Voltage Source. 7

Problem.. 8

Convert Following Current Source to Voltage Source. 8

Voltage and Current Source Conversion

There are two type of sources.

1. · Ideal Sources
2. · Real Sources

Ideal Sources

Ideal source is a source , which supply same voltage / current on its terminal for unlimited span of time. It should be remember that ideal source do not exist in real life

Real Sources

Real sources, represent real life model. Their out put voltage / current decrease with the span of time.

1. VL= Ideal Source
2. Vs= Real Source

Normally to power up a circuit two type of sources can be used.

a. Voltage Source

b. Current Source

Although in real life , we do not have any thing like current source, how ever in texts and theory , current source does exist. Some time conversion of One source to another , help us t solve the problem easily

Real Source (Voltage)

All real sources has some type of internal resistance. They are mainly offered due to structure and composition of courses. Although while during calculations we normally ignore the internal resistance However the internal resistance causes terminal voltage to decrease when current is drawn from its terminals

Solution

A voltage source has an internal resistance of 2 W

a) Find the terminal voltage 22 W load is connected across its terminals

b) Find the current in the load

Constant Current Sources

1. Maintains same current in branch of circuit

2. Doesn’t matter how components are connected external to the source

3. Direction of current source indicates direction of current flow in branch

Real Source (Current)

1. AS real voltage source can be repressed as ideal current source in parallel with inter resistance

2. Causes terminal voltage to decrease when current is drawn from its terminals

Example

When a 1 KΩ load is connected across at 20 – mA , it is found that only 18 mA flows in load. What is internal Resistance of the source ?

Solution

We need to Find Internal Resistance

The Formula is

R internal =

We have I but do not have V. Remember that the circuit is in parallel configuration. If we find voltage in one branch , it will be same for other

So voltage for branch 2

V= IxR = 18mA x 1 KΩ =18V

Now Back to Resistance of Branch 1 = R internal =

= =9K Ω

Source Conversion

1. A real voltage Source can be converted to equivalent real current source , and vice versa.

2. When Conversion is made, the sources are equivalent

Converting a Voltage Source to a Current Source

The voltage source can be converted to an equivalent current source by:

IS = VS/RS

For Example

Converting a Current Source to a Voltage Source

Similarly vice versa conversion can be made in similar fashion

Problem

Convert Following Current Source to Voltage Source

Solution