Electrical circuits lecture notes b. Tech

R
Th
while all sources are replaced by their internal resistors at ideal condition i.e. 
voltage source is short circuit and current source is open circuit. 
(a)
(b) 
Figure (a)
 
shows a simple block representation of a network with several active / passive
 
elements with the load resistance 
R
L
connected across the terminals 
‘a
&
b’
and figure (b) shows 
the 
Thevenin equivalent circuit 
with
 V
Th
 
connected across
 R
Th
 
&
 R
L
 .
Main steps to find out V
Th
 and R
Th
 : 
1.
The terminals of the branch/element through which the current is to be found out are 
marked as say 
a & b
after removing the concerned branch/element. 

---

2.
Open circuit voltage 
V
OC
across these two terminals is found out using the conventional 
network mesh/node analysis methods and this would be 
V
Th
.
3.
Thevenin resistance R
Th
is found out by the method depending upon whether the 
network contains dependent sources or not. 
a.
With dependent sources: 
R
Th
= V
oc
/ I
sc
b.
Without dependent sources : 
R
Th
= 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