Source transformation:
A current source or a voltage source drives current through its load resistance and the
magnitude of the current depends on the value of the load resistance.
Consider a practical voltage source and a practical current source connected to the same load
resistance RL
as shown in the figure
R1’s in figure represents the internal resistance of the voltage source VS and current source IS.
Two sources are said to be identical, when they produce identical terminal voltage VL and load current
IL.
The circuit in figure represents a practical voltage source & a practical current source respectively, with
load connected to both the sources.
The terminal voltage VL and load current IL across their terminals are same.
Hence the practical voltage source & practical current source shown in the dotted box of figure are
equal.
The two equivalent sources should also provide the same open circuit voltage & short circuit current.
From fig (a)
From fig (b)
IL =
IL =
I
=
I
VS = IR or I =
Hence a voltage source Vs in series with its internal resistance R can be converted into a current source
I =
, with its internal resistance R connected in parallel with it. Similarly
a current source I
in parallel with its internal resistance R can be converted into a voltage source V = IR in series with its
internal resistance R.
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