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INC 111 Basic Circuit Analysis

INC 111 Basic Circuit Analysis. Week 5 Thevenin’s Theorem. Special Techniques. Superposition Theorem Thevenin’s Theorem Norton’s Theorem Source Transformation. Linearity Characteristic. If R L change its value , how will it effect the current and voltage across it?. I.

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INC 111 Basic Circuit Analysis

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  1. INC 111 Basic Circuit Analysis Week 5 Thevenin’s Theorem

  2. Special Techniques • Superposition Theorem • Thevenin’s Theorem • Norton’s Theorem • Source Transformation

  3. Linearity Characteristic If RL change its value , how will it effect the current and voltage across it?

  4. I Voc = Voltage open-circuit Isc = Current short-circuit ISC V VOC For any circuit constructed from only linear components Not just RL, all resistors have this property.

  5. Thevenin’s Theorem When we are interested in current and voltage across RL, we can simplify other parts in the circuit. Equivalent circuit

  6. I ISC Slope = RL change value V VOC Voc = Voltage open-circuit Isc = Current short-circuit Rth = Rth equivalent

  7. Thevenin’s Equivalent Circuit Thevenin’s equivalent circuit VTH = Voc (by removing RL and find the voltage difference between 2 pins) RTH (by looking into the opened connections that we remove RL, see how much resistance from the connections. If we see a voltage source, we short circuit. If we see a current source, we open circuit.)

  8. Why do we needequivalent circuit? • To analyze a circuit with several values of RL • For circuit simplification(source transformation) • To find RL that gives maximum power (maximum power transfer theorem)

  9. Procedure • Remove RL from the circuit • Find voltage difference of the 2 opened connections. Let it equal VTH. • From step 2 findRTH by • 3.1 short-circuit voltage sources • 3.2 open-circuit current sources • 3.3 Look into the 2 opened connections. Find equivalent resistance.

  10. Example Find Thevenin’s equivalent circuit and find the current that passes through RL when RL = 1Ω

  11. 6V 10V 6V 0V 0V 0V Find VTH

  12. Find RTH Short voltage source RTH

  13. Thevenin’s equivalent circuit If RL = 1Ω, the current is

  14. Example Find Thevenin’s equivalent circuit

  15. 3V 5V 3V 0V 0V 0V Find VTH

  16. Find RTH Open circuit current source RTH

  17. Thevenin’s equivalent circuit

  18. Example: Bridge circuit Find Thevenin’s equivalent circuit

  19. 10V Find VTH 8V 2V 0V VTH = 8-2 = 6V

  20. Find RTH RTH

  21. Thevenin’s equivalent circuit

  22. Special Techniques • Superposition Theorem • Thevenin’s Theorem • Norton’s Theorem • Source Transformation

  23. I ISC V VOC For any point in linear circuit

  24. Thevenin’s Equivalent Circuit

  25. Norton’s Equivalent Circuit In= Isc from replacing RL with an electric wire(resistance = 0) and find the current Rn = RTH (by looking into the opened connections that we remove RL, see how much resistance from the connections. If we see a voltage source, we short circuit. If we see a current source, we open circuit.)

  26. Example Find Norton’s equivalent circuit and find the current that passes through RL when RL = 1Ω

  27. Find R total Find I total Current divider Find In

  28. Find Rn Short voltage source RTH

  29. Norton’s equivalent circuit IfRL = 1Ω, the current is

  30. Relationship BetweenThevenin’s and Norton’s Circuit I ISC Slope = - 1/Rth V VOC

  31. Norton’s equivalent circuit Thevenin’s equivalent circuit Same R value

  32. Example Find Norton’s equivalent circuit

  33. Current divider Find In

  34. Find RTH Open circuit current source RTH

  35. Norton’s equivalent circuit

  36. Thevenin’s equivalent circuit Norton’s equivalent circuit 0.2 x 15 = 3

  37. Equivalent Circuits withDependent Sources We cannot find Rth in circuits with dependent sources using the total resistance method. But we can use

  38. Example Find Thevenin and Norton’s equivalent circuit

  39. I2 I1 KVL loop1 KVL loop2 Find Voc

  40. I2 I1 Solve equations I1 = 3.697mA I2 = 3.678mA

  41. I2 I1 I3 KVL loop1 KVL loop2 KVL loop3 Find Isc

  42. I2 I1 I3 Find Isc I1 = 0.632mA I2 = 0.421mA I3 = -1.052 A Isc = I3 = -1.052 A

  43. Norton’s equivalent circuit Thevenin’s equivalent circuit

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