Electrical circuits lecture notes b. Tech

V
OC
across these two terminals and 
I
SC
through these two terminals 
are found out using the conventional network mesh/node analysis methods and they are 
same as what we obtained in Thevenin’s equivalent circuit
.
3.
Next 
Norton resistance R
N
is found out depending upon whether the network contains 
dependent sources or not. 
a)
With dependent sources: 
R
N
= V
oc
/ I
sc
b)
Without dependent sources : 
R
N
=
Equivalent resistance looking into the 
concerned terminals with all voltage & current sources replaced by their internal 
impedances (i.e. ideal voltage sources short circuited and ideal current sources 
open circuited) 
4.
Replace the network with 
I
N
in parallel with 
R
N
and the concerned branch resistance 
across the load terminals(A&B) as shown in below fig 
 
Example:
Find the current through the resistance R
L
(1.5 Ω) of the circuit shown in the 
figure (a) below using Norton’s equivalent circuit.? 
Fig(a) 
Solution: 
To find out the Norton’s equivalent ckt we have to find out
I
N
 
=
I
sc
,R
N
=V
oc
/
I
sc
. 
Short the 1.5Ω load resistor as shown in (Fig 2), and Calculate / measure the Short Circuit 
Current. This is the Norton Current (I
N
). 
 
Fig(2)

---

We have shorted the AB terminals to determine the Norton current, I
N.
The 6Ω and 3Ω are then 
in parallel and this parallel combination of 6Ω and 3Ω are then in series with 2Ω.So the Total 
Resistance of the circuit to the Source is:- 
2Ω + (6Ω || 3Ω) ….. (|| = in parallel with) 
R
T
= 2Ω + [(3Ω x 6Ω) / (3Ω + 6Ω)]
R
T
= 2Ω + 2Ω
R
T
= 4Ω 
I
T
= V / R
T 
I
T
= 12V / 4Ω= 3A.. 
Now we have to find I
SC
= I
N
… Apply CDR… (Current Divider Rule)… 
I
SC
= I
N
= 3A x [(6Ω / (3Ω + 6Ω)] = 2A.