thevenin theorem. SLIDE NUMBER 3 EXPLANATION OF THEOREM: it is possible to simplify any electrical circuit, no matter how complex, to an equivalent two-terminal circuit with just a single constant voltage source in series with a resistance (or impedance) connected to a load. SLIDE NUMBER 4 INVENTION STORY THE THEOREM WAS INDEPENDENTLY DERIVED IN 1853 BY THE GERMAN SCIENTIST HERMANN VON HELMHOLTZ. SLIDE NUMBER 5 EXPLANATION OF Thevenin’s equivalent circuit As far as the load resistor RL is concerned, any complex “one-port” network consisting of multiple resistive circuit elements and energy sources can be replaced by one single equivalent resistance Rs and one single equivalent voltage Vs. Rs is the source resistance value looking back into the circuit and Vs is the open circuit voltage at the terminals. SLIDE NUMBER 6 EXPLANATION OF DIAGRAM 1 Let us consider a simple DC circuit as shown in the figure above, where we have to find the load current IL by the Thevenin’s theorem. In order to find the equivalent voltage source, rL is removed from the circuit as shown in the figure below and Voc or VTH is calculated. SLIDE NUMBER 7 EXPLANATION OF DIAGRAM 2 Now, to find the internal resistance of the network (Thevenin’s resistance or equivalent resistance) in series with the open circuit voltage VOC , also known as Thevenin’s voltage VTH, the voltage source is removed or we can say it is deactivated by a short circuit (as the source does not have any internal resistance) SLIDE NUMBER 9 As per Thevenin’s Statement, the load current is determined by the circuit shown above and the equivalent Thevenin’s circuit is obtained. Where, VTH is the Thevenin’s equivalent voltage. It is an open circuit voltage across the terminal AB known as load terminal RTH is the Thevenin’s equivalent resistance, as seen from the load terminals where all the sources are replaced by their internal impedance rL is the load resistance Steps for Solving Thevenin’s Theorem Step 1 – First of all remove the load resistance rL of the given circuit. Step 2 – Replace all the impedance source by their internal resistance. Step 3 – If sources are ideal then short circuit the voltage source and open the current source. Step 4 – Now find the equivalent resistance at the load terminals know as Thevenin’s Resistance (RTH). Step 5 – Draw the Thevenin’s equivalent circuit by connecting the load resistance and after that determine the desired response. Slide number-10 Thevenin Voltage The Thevenin voltage e used in Thevenin's Theorem is an ideal voltage source equal to the open circuit voltage at the terminals. In the example below, the resistance R2 does not affect this voltage and the resistances R1 and R3 form a voltage divider Slide number-11 Thevinin resistance The Thevenin resistance r used in Thevenin's Theorem is the resistance measured at terminals AB with all voltage sources replaced by short circuits and all current sources replaced by open circuits.

1. Circuit Theory & Networks
TOPIC: ThÉvenin's Theorem
ELECTRONICS AND TELECOMMUNICATION
ENGINEERING
SECOND YEAR
1. ARPITA BANERJEE
2. ROHAN HORE
3. SOUMYA GHOSH CHOWDHURY
4. RANIK AHAMED
Presented By-

2. INDEX
1. THEOREM
2. DEVELOPED BY
3. Thevenin’s equivalent circuit
4. EXPLANATION
5. Thevenin Voltage
6. Thevenin Resistance
7. Why Thevenin's theorem is not applicable to non-linear circuits?
8. Can Thevenin theorem be applied to circuit having A.C sources?
9. Why Thevenin equivalent circuit is not very useful at microwave frequencies?
10. APPLICATIONS
11. Advantages
12. LIMITATIONS

3. THEOREM:
– THEVENIN’S THEOREM STATES THAT “ANY LINEAR CIRCUIT CONTAINING
SEVERAL VOLTAGES AND RESISTANCES CAN BE REPLACED BY JUST ONE
SINGLE VOLTAGE IN SERIES WITH A SINGLE RESISTANCE CONNECTED
ACROSS THE LOAD“.

4. DEVELOPED BY-
– IN 1883 THE THEOREM WAS DEVELOPED BY LÉON CHARLES
THÉVENIN (1857–1926), AN ELECTRICAL ENGINEER WITH FRANCE'S
NATIONAL POSTES ET TÉLÉGRAPHES TELECOMMUNICATIONS
ORGANIZATION.

5. Thevenin’s equivalent circuit:

6. EXPLANATION:
THE THEVENIN’S STATEMENT IS EXPLAINED WITH THE HELP OF A CIRCUIT
SHOWN BELOW.
STEP- 1 :

7. STEP-2 :

8. STEP-3 :

9. STEP-4 :

10. Thevenin Voltage:

11. THEVENINRESISTANCE:

12. Why Thevenin's theoremis not applicable to non-linear circuits?
– THE THEVENIN'S THEOREM CAN BE USED IN NON LINEAR CIRCUITS, AS LONG AS IT'S USED AT LINEAR (OR APPROX
LINEAR) PARTS OF THE CURVE.
FOR EXAMPLE, LET'S LOOK AT COMMON EMITTER AMPLIFIER.

13. Why Thevenin's theoremis not applicable to non-linear
circuits?

14. CAN THEVENINTHEOREMBE APPLIED TO CIRCUIT
HAVING A.C SOURCES?
YES. THEVENIN'S THEOREM IS APPLICABLE TO BOTH AC AND DC SOURCES.

15. WHY THEVENIN EQUIVALENT CIRCUITIS NOT VERY USEFULAT
MICROWAVE FREQUENCIES?
– WHEN IT GETS TO MICROWAVES, THE LENGTH OF THE WIRES START TO
GET COMPARABLE TO THE WAVELENGTH OF YOUR SIGNAL, SO YOU START
TO GET SOME WEIRD THINGS LIKE STATIONARY WAVE PATTERNS ON
YOUR CIRCUIT AND THE CONNECTION BETWEEN ELEMENTS BECOME
WAVE GUIDES, THE CIRCUIT STARTS TO INTERFERE WITH ITSELF
DEPENDING ON THE PHYSICAL DISPOSITION OF ELEMENTS. THEVENIN
DOESN'T CONSIDER THOSE DIFFERENCES IN THE CIRCUIT MODELING, SO
IT'S NOT GOOD ENOUGH IN THIS CASE.

16. APPLICATIONS:
– 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.
– SOURCE MODELING AND RESISTANCE MEASUREMENT USING THE
WHEATSTONE BRIDGE PROVIDE APPLICATIONS FOR THEVENIN’S
THEOREM.
– THIS HELPS IN MAKING INTEGRATED CIRCUITS.

17. ADVANTAGES:
– IT REDUCES A COMPLEX CIRCUIT TO A SIMPLE
CIRCUIT VIZ A SINGLE SOURCE OF E.M.F
– IT GREATLY SIMPLIFIES THE PORTION OF THE
CIRCUIT OF THE LESSER IMPORTANCE AND
ENABLES US TO VIEW THE ACTION OF THE OUTPUT
PART DIRECTLY.
– THE THEOREM IS PARTICULARLY USEFUL TO FIND
CURRENT IN A PARTICULAR BRANCH OF A
NETWORK AS THE RESISTANCE OF THAT BRANCH IS
VARIED WHILE ALL OTHER RESISTANCES AND E.M.F
SOURCE REMAIN CONSTANT.

18. LIMITATIONS:
– MANY, IF NOT MOST CIRCUITS ARE ONLY LINEAR OVER A CERTAIN RANGE
OF VALUES, THUS THE THÉVENIN EQUIVALENT IS VALID ONLY WITHIN
THIS LINEAR RANGE AND MAY NOT BE VALID OUTSIDE THE RANGE.
– THE THÉVENIN EQUIVALENT HAS AN EQUIVALENT I-V CHARACTERISTIC
ONLY FROM THE POINT OF VIEW OF THE LOAD.
– THE POWER DISSIPATION OF THE THÉVENIN EQUIVALENT IS NOT
NECESSARILY IDENTICAL TO THE POWER DISSIPATION OF THE REAL
SYSTEM.

19. THANK YOU