S5 Topic

1. Ideal voltage & current sources
Anilkumar K M
MSM College
Kayamkulam

2. Ideal Voltage Source
• A voltage source is a device which provides a constant voltage to load at any
instance of time and is independent of the current drawn from it.
• This type of source is known as an ideal voltage source
• It has zero internal resistance

3. • Voltage sources that have some amount of internal resistance are known as a
practical voltage source.
• Due to this internal resistance, voltage drop takes place.
• A practical voltage source is thus denoted by a resistance in series which represents
the internal resistance of source.

4. Ideal Current Source
• A current source is a device which provides the constant current to load at any time
and is independent of the voltage supplied to the circuit.
• This type of current is known as an ideal current source
• practically ideal current source is also not available.
• It has infinite resistance

5. Practical Current source
• Practically current sources do not have infinite resistance across there but
they have a finite internal resistance.
• So the current delivered by the practical current source is not constant and it
is also dependent somewhat on the voltage across it.

6. • The examples of current source are solar cells, transistors
• examples of some voltage sources are batteries and alternators.
Why ideal Current source has infinite resistance?
A current source is used to power a load, so that load will turn on. We try to supply 100% of the power to load.
For that, we connect some resistance to transfer 100% of power to load because the current always takes the
path of least resistance. So, in order for current to go to the path of least resistance, we must connect resistance
higher than load. This is why we have the ideal current source to have infinite internal resistance. This infinite
resistance will not affect voltage sources in the circuit.