1. THEVENIN THEOREM & NORTON
Lecture 06
THEVENIN THEOREM & NORTON

2. OBJECTIVES
Apply Thevenin’s theorem to simplify AC circuits for analysis.
List the steps for determining the Thevenin Equivalent of an actual electronic circuit.
Using Thevenin’s theorem, analyze complex series-parallel circuits with multiple load values.
Calculate the average power dissipated by a load.

3. THÉVENIN’S THEOREM
Used to reduce an AC circuit to a single voltage source “VTH” in series with a single Impedance “ZTH “

4. THEVENIN VOLTAGE “VTH” is:
the “Open Circuit Voltage” measured across the load, with the load removed.

5. THEVENIN IMPEDANCE “ZTH ” is:
the “Total Equivalent Impedance” of the circuit as seen from the load position with the load removed and all sources zeroed.

6. Steps for Thevenin circuit
Step 1: Open the two terminals between which you want to find the Thevenin circuit.
Step 2: Determine the voltage across the terminals.
Step 3: Determine the impedance viewed from the terminals with all sources zeroed.
Step 4: Connect VTH and ZTH in series to produce the Thevenin Equivalent circuit.

7. Step 5: Redraw the Thevenin equivalent circuit as a single Impedance “ZTH” in series with the load impedance “ZL” and voltage source “ETH”.

8. Ex: Calculate the Thévenin Equivalent circuit.
Given: Vs = 25<0 V; R1 = 100Ω ; R2 = 25 Ω; RL = 1kΩ, XL = 80 Ω, f = 509 Hz

9. Solution: Find VTH

10. Calculate VTH (open circuit)

11. Find ZTH

12. Calculate ZTH

13. Draw Thevenin equivalent circuit

14. Ex: NORTON THEOREM

15. STEP 1: Find ZN = ZTH

16. Calculate ZN = ZTH

17. STEP 2: Find IN = Isc

18. Calculate IN = Isc
Note that,

19. Equation for Mesh 1

20. Equation for Mesh 2

21. Calculate IN

22. Norton Equivalent Circuit

23. NORTON THEOREM

24. THEVENIN THEOREM

25. RELATIONSHIP
Keep in mind that the two equivalent circuits (Thevenin and Norton) are related as:

26. RELATIONSHIP