Lecture 12
Source Transformation
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Source Transformation
Basis for Thevenin and Norton Equivalent
Circuits
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Source Transformation
• We have noticed that series-parallel
combination and wye-delta transformation help
simplify circuits.
• Source transformation is another tool for
simplifying circuits.
• Basic to these tools is the concept of
equivalence.
– an equivalent circuit is one whose v-i characteristics
are identical with the original circuit.
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Source Transformation
• A source transformation is the process of
replacing a voltage source vs in series with a
resistor R by a current source is in parallel with
a resistor R, or vice versa.
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Source Transformation
• Source transformation also applies to dependent
sources, provided we carefully handle the
dependent variable.
– A dependent voltage source in series with a resistor can be
transformed to a dependent current source in parallel with
the resistor or vice versa.
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Equivalence
• An equivalent circuit is one in which the iv characteristics are identical to that of the
original circuit.
– The magnitude and sign of the voltage and
current at a particular measurement point are
the same in the two circuits.
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Example 1…
• Find an equivalent current source to replace Vs
and Rs in the circuit below.
IL
VL
RL
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…Example 1…
• Find IL and VL.
VL =
RL
VS
RL + RS
VL =
6k
18V = 12V
6k + 3k
IL
VL
RL
I L = VL / RL
I L = 12V / 6k = 2mA
PVs = PL + PRs
PVs = 12V (2mA) + (18V − 12V )(2mA)
PVs = 36mW
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Example 2…
• Find an equivalent voltage source to replace Is
and Rs in the circuit below.
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…Example 2…
• Find IL and VL.
50
IS
300 + 50
I L = 0.714mA
IL =
VL = I L RL
VL = 0.714mA(300) = 0.214V
PVs = PL + PRs
PVs = 0.214V (0.714mA)
+ 0.214V (5mA − 0.714mA)
PVs = 1.07mW
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Example 3
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Example 4
• Use source
transformation to find
v0 in the circuit.
– Use current division
– or
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Example 5
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Example 6
• Use source transformation to find i0 in the
circuit.
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Thank You
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