1. Lecture-4

2. Md.Kausher ahmed Electrical department

3. Electrical engineering-1 Code-6723

4. Lesson declared The venin's theorem

5. After, previous class………….

6. Importance of Thevenin’s theorem: In circuit analysis Thevenin’s theorem is very important. It is helpful simplifying a circuit. A large circuit can be replaced with an independent voltage source and a resistor. This replacement system is very helpful tool in circuit design. According to Thevenin’s theorem we replace a huge circuit with Thevenin’s equivalent, actually original circuit behaves same as Thevenin’s equivalent.

7. Continue……… Consider a linear two terminal circuit shown in figure 4(a).

8. Continue…….. Let us find that what will make two circuits are equivalent. If we remove the load from figure 1(a), the voltage source will be open circuit then voltage source of figure 1(a) must equal to voltage source V Th in figure 1(b). So the two circuits will become equivalent and open circuit voltage across two terminals is V Th = V oc

9. Fig :Thevenin’s theorem And figure 2(a) shows that

10. Continue…… Load current I L and voltage across the load v L can be easily determined if the Thevenin’s equivalent circuit at the load terminals is obtained shown in figure 4(b).

11. Continue……

12. Thevenin’s theorem problem: Find the Thevenin’s equivalent circuit of the circuit shown in figure 5, to the left of the terminals a-b. Then find the current through R L = 6, 16, 36Ω.

13. Answer Turning off voltage source and making short circuit and 2A current circuit replacing it open circuit we get the circuit shown in figure 6 (a)

14. Continue……. To find V Th applying mesh analysis consider figure 6(b).

15. Continue……. In two loops applying mesh analysis we get, -32 + 4i 1 + 12 (i 1 – i 2 ) = 0, i 2 = -2A i 1 = 0.5A. In this way V Th = 12 (i 1 – i 2 ) = 30v

16. Continue……. We can use alternative way nodal analysis or source transformation to find V Th. nodal analysissource transformation The Thevenin’s equivalent circuit shown in figure 7.

17. We know I L = V Th / (R Th + R L ) = 30 / (4 + R L ) When R L = 6, I L = 30/10 = 3A When R L = 16, I L = 30/20 = 1.5A When R L = 36, I L = 30/40 = 0.75A

18. Feedback # Explain Thevenin’s theorem. Find the Thevenin’s equivalent circuit of the circuit shown in figure 5, to the left of the terminals a-b. Then find the current through R L = 6, 16, 36Ω.