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a
-
a´
by all the independent sources within the network N
1 
when the 
output terminals are kept open. Therefore, it is called the open-circuit voltage. R
o
will again be the 
equivalent resistance of the deactivated network seen from 
a
-
a´
. The resulting equivalent circuit for 
N
1
is called its Thevenin’s Equivalent.

---

5.24
Circuit Theorems
Thevenin’s Equivalent may also be derived from Norton’s Equivalent by applying Source 
Transformation Theorem.
thevenin’s theorem
Let a network with unique solution be represented as interconnection of two networks 
N
1
and 
N
2
and let the interaction between 
N
1
and 
N
2
be only through the two terminals 
at which they are connected. 
N
1
is linear and 
N
2
may be linear or non-linear. Then, the 
network 
N
1
may be replaced by an independent voltage source of value 
v
oc
(
t
) in series 
with a resistance 
R
o
without affecting any voltage or current variable within 
N
2
provided 
the resulting network has unique solution. 
v
oc
(
t
) is the voltage that will appear across the terminals when they are kept open and 
R
o
is the equivalent resistance of the deactivated circuit (‘dead’ circuit) seen from the 
terminals.
This equivalent circuit for 
N
1
is called its 
Thevenin’s Equivalent.
+
+
–
–
i
(
t
)
v
oc
(
t
)
R
o
i
(
t
)
v
(
t
)
Linear memoryless 
circuit with many 
independent and 
dependent sources
N
1
N
2
Linear or 
non-linear
circuit
N
2
Linear or 
non-linear
circuit
a
a
+
–
v
(
t
)
a
a
Fig. 5.5-4 
Thevenin’s theorem and Thevenin’s equivalent