Thevenin dependent Ohms Law tells us that V = I*R so Equivalent - PowerPoint PPT Presentation

2/24/20 Equivalent Resistance • Equivalent resistance and voltage are terminal- Thevenin dependent • Ohm’s Law tells us that V = I*R so… Equivalent Circuit 2 • R = V / I • Electrical resistance is the ratio of: • The (open circuit) voltage across a pair of nodes to • The (short circuit) through the pair of nodes EGR 220, Chapter 4 February 25, 2020 2 1 2 Thevenin Equivalent – Process • Equivalent circuits concept 1) Find R Th : a) Indistinguishable from each other, b) …In terms of the V – I – R eq characteristics, c) …At the specified terminals (nodes) 2) Find V Th : 3 4 3 4 1

2/24/20 Thevenin Equivalent – Process Thevenin: Find V Th , R Th 1) Find R Th : – Find R Th – a) Remove the load resistor ( if there is one ) b) Set all (independent) sources equal to zero. • V-source = 0V ð < open / short > • I-source = 0A ð < open / short > c) Find the equivalent resistance from the specified nodes 2) Find V Th : a) Return to the original circuit, remove the load again, but keep all sources, and b) Find the open-circuit voltage across the specified nodes 5 6 5 6 Thevenin: Find V Th , R Th Thevenin: Find V Th , R Th – Nodal Analysis – – Mesh Analysis – 7 8 7 8 2

2/24/20 Thevenin: Find V Th , R Th Thevenin: Find V Th , R Th – Source Transformation, 2A – – Source Transformation, 30V – 9 10 9 10 Maximum Power Transfer * Maximum Power Transfer * • How do we find the P max the circuit can deliver to R L ? 11 12 11 12 3

2/24/20 Maximum Power Transfer Concept Question • Are equivalent circuits all the same? • Discuss V Th , R Th at a-b and b-c • What is R L for maximum power transfer, and how do you find the amount of power transferred? 13 14 13 14 Thevenin Equivalent Thevenin Equivalent 15 16 15 16 4

2/24/20 Thevenin Equivalent 2 Thevenin Equivalent 2 17 18 17 18 Thevenin Self-Review For the next homework: a to c (Thevenin equivalent for b to c is posted) • What is a Thevenin Equivalent Circuit? • Draw a generic Thevenin equivalent circuit • Discuss and write down 3 good uses for a Thevenin equivalent circuit, or for the Thevenin theorem • How might you find the maximum power that can be delivered to any load from any circuit? • Why is this an important question? 19 20 19 20 5

2/24/20 Norton Equivalent Circuit Summary • Source transformation = V v • Equivalency Th oc • Equivalent resistance • Voltage – Current – R eq behavior = I i • Thevenin equivalent circuit N sc • V-source & series resistor v • Uses for Thevenin equivalent circuits = = = R R R oc • Only need to know the Norton equivalent exists. We will Th N in focus on Thevenin i sc 21 22 21 22 Questions? 23 6