Thevenin's theorem and application

1. Thevenin’s Theorem and its Application
By
Dr G R Sinha
IEEE Senior Member & Fellow IETE
Professor, Department of Electronics and Communication Engineering
CMR Technical Campus, Hyderabad

2. Outline of Lecture
 Lecture Objectives
 Thevenin’s Theorem
 Examples
 Application
2Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

3. Lecture Objectives
 To understand Thevenin’s theorem and simplify electrical networks
into simple equivalent circuits using the theorem.
 To study an application of the theorem.
+_20 V
5 
20 
10 
17 
1.5 A
A
B

An example of Network Transistor Circuit
3
11 22
Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

4. Thevenin's Theorem
Thevenin’s theorem states that a linear and bilateral network can be
replaced by an equivalent circuit consisting of a voltage source VTh in
series with a resistance RTh.
where VTh is the open-circuit voltage across load terminals, and RTh is the input or
equivalent resistance at the terminals when all the independent sources are turned
off.
4
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Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

5. Determination of RTh (Thevenin’s Resistance):
The resistance seen by the load, with removed load and all independent
sources turned off (Voltage sources replaced by short circuits & current
sources replaced by open circuits).
Thevenin's Theorem (contd..)
5
11
22
33
44
Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

6. Determination of VTh (Thevenin’s Voltage):
The voltage across the load under open circuit condition, also called as
open circuit voltage.
Thevenin's Theorem (contd..)
6
11
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Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

7. 2
10V 5V
2 2
OC Thv V  

5VThV 
2ThR  
2 2
1 2
2 2
ThR

   

Example # 1
7
11
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Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

8. Example # 2
8
12  4 
6  2  VX30 V +_
+
_
A
B


12  4 
6 30 V +_
A
B


(30)(6)
10
6 12
ABV V 

12  4 
6 
A
B


RTH = 12||6 + 4 = 8 
11
22
33
Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

9. +_20 V
5 
20 
10 
17 
1.5 A
A
B


9
Example # 3
+_20 V
5 
20 
10 
1.5 A
A
B


5 
20 
10 
A
B


11 22
33
44
Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

10. Example # 4
Determining the voltage drop across RL
11
22
33
VAB = −20 −(−12) = −8V
RTh = RTA + RTB = 2 + 2.4 = 4.4 Ω
44
10Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

11. 11
Example # 5
Find the voltage across the 100  load.
+_ 86 V
50 
30 
40 
100 
6 IS
IS


A
B
+_ 86 V
50 
30 
40 
6 IS
IS


A
B
86 80 6 0 1
6 30 36
S S S
AB S S
I I I A
V I I V
     
   
50 
30 
40 
6 IS
IS


A
B
RTH
50 
30 
40 
6 IS
IS
1 A
1 A
IS + 1 V
50 30( 1) 6 0S S SI I I   
15
43
SI A


11 22
33 44
22
Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

12. 50 
30 
40 
6 IS
IS
1 A = I
1 A
IS + 1 V
15
50 1(40) 0
43
V
 
   
 
57.4V volts
57.4
1
TH
V V
R
I
   
12
Example # 5 (contd..)
+_
RTH
VTH
57.4 
36 V 100 
100
36 100
22.9
57.4 100
x
V V 

55
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Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

13. Applications of Thevenin’s Theorem
 To determine Change in Load Voltage: To predict range of load
voltage variation due to change in load resistance.
 To obtain Norton’s equivalent circuit.
 To determine Maximum power that can be transferred to Load
from the network.
13Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

14. Maximum Power Transfer Theorem
Maximum power transfer from a circuit to a variable load occurs
when the load resistance equals the source resistance , RL = RTH.
LR
i
ThR
ThV
 
22
L Th Th L Lp i R V R R R    
This power is maximum when
0Lp R  
L ThR R
 
2
max L Th
Th Th L L R R
p V R R R 
   
 
2 2
max 2 4Th Th Th Th Thp V R R V R   
This gives:
14Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017

15. Sincere Thanks with Inspiring Equation
E= mc2
E=Excellence, m = Motivation, C =Commitment
c = 0.5 (Half hearted) E = ¼
c = 2 (Doubly enthused) E =4
Thevenin’s Theorem and its Application by G R Sinha 9th June, 2017