LEC5_Thevenin (PDF) - Applied Health Sciences Technology - Introduction to Electrical Engineering

Applied Health Sciences Technology Introduction to Electrical Engineering Lecture 5 Thevenin Theorem Academic Year: 2024-2025 Dr. Mahmoud Elgamasy Thevenin Theorem  Thevenin Theorem 𝑅𝑡ℎ R thévenin (Thévenin equivalent resistance...

Applied Health Sciences Technology Introduction to Electrical Engineering Lecture 5 Thevenin Theorem Academic Year: 2024-2025 Dr. Mahmoud Elgamasy Thevenin Theorem  Thevenin Theorem 𝑅𝑡ℎ R thévenin (Thévenin equivalent resistance): It is the equivalent resistance of the entire circuit as seen from the two terminals where the load is connected. To find Rthévenin, you: Remove the load resistor. Replace all independent voltage sources with short circuits and all independent current sources with open circuits. Calculate the resistance seen from the open terminals. Vth V thévenin (Thévenin equivalent voltage): This is the open-circuit voltage across the two terminals where the load is connected. It represents the voltage that would appear across the load if it were disconnected.  Example 1: Find Thevenin equivalent circuit The battery has an internal resistance ‘r’ Thevenin voltage 𝑉𝑡ℎ 𝑉𝑡ℎ E ER 2 I = V th = IR 2 = R1 + R 2 + r R1 + R 2 + r Thevenin voltage 𝑅𝑡ℎ R 2 (R1 + r ) R th = R 2 / /(R1 + r ) = R 2 + (R1 + r )  V th I = R th + R L Example 2: Calculate the current in the resistor R by using Thevenin theorem 4 R=4 12 V 4  Answer 4 A 4 12 V B  Answer Thevenin voltage 4 4 A + A 1.5 A 4 4 12 V B 12 V B - 𝑉𝑡ℎ = 𝑉𝐴𝐵 = 1.5 ∗ 4 = 6 V 𝑉𝑡ℎ = 6 V  Answer Thevenin resistance 4 A A A 4 4 2 B 4 B B 𝑅𝑡ℎ =2 Ω  Answer 4 Rth = 2 A A 4 Vth = 6 V 12 V B B  Answer 4 Rth = 2 A R=4 R=4 Vth = 6 V 12 V 4 B 6 6 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑛 𝑅 = = =1𝐴 2+4 6 Example 3: Find Thevenin equivalent circuit 10 5 A 12 V 10 10 B Answer Finding Rth 10 5 A 10 10 B Answer Finding Rth 5 A A 10 10 5 10 B B A 5 𝑅𝑡ℎ = 5 Ω B Answer Finding Vth 10 5 A 12 V ?? 10 Vth = VAB 10 B Vth = VAB  10 5 Answer Finding Vth 12 V 10 10 10 12 V 15 10 10 0.75 A 12 V 12 V 6 16  10 5 Answer Finding Vth 12 V 10 10 10 12 V 15 10 10 0.75 A 12 V 12 V 6 16 Answer Finding Vth 0.75 A 10 5 A 12 V I 10 10 B 10 𝐼 = 0.75 ∗ = 0.3 𝐴 10 + 15 𝑉𝑡ℎ = 0.3 ∗ 10 = 3 𝑉  Answer 10 5 A Rth = 5 A 12 V Vth = 3 V 10 10 B B