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Thevenin and Norton Equivalent Circuits

Any Circuit. I AB. A. + V AB -. Circuit A ( Linear ). Circuit B. B. Thevenin and Norton Equivalent Circuits. Read: pages 120 – 133 Problems: 4.53 and 4.68 (Due 10/29/01).

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Thevenin and Norton Equivalent Circuits

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  1. Any Circuit IAB A + VAB - Circuit A (Linear) Circuit B B Thevenin and Norton Equivalent Circuits Read: pages 120 – 133 Problems: 4.53 and 4.68 (Due 10/29/01) Consider any circuit divided into separate circuits, where the two parts are connected at two points A and B as shown. ENGR-201 Thevenin's Theorem

  2. IAB RTH IAB A A + - + VAB - + VAB - Circuit A (Linear) VTH Circuit B Circuit B B B Thevenin’s Theorem Everything inside the linear circuit (A) can be replaced by an equivalent circuit that consists of two components, an ideal voltage source in series with a resistor. Two circuits are equivalent if they produce the same load voltage and current (VAB and IAB) for every possible load condition. ENGR-201 Thevenin's Theorem

  3. IAB IAB A A + VAB - + VAB - Circuit A (Linear) IN Circuit B Circuit B RN B B Norton’s Theorem Everything inside the linear circuit (A) can be replaced by an equivalent circuit that consists of two components, an ideal current source in parallel with a resistor. The trick is to find the values of VTH and RTH (IN and RN). ENGR-201 Thevenin's Theorem

  4. A IAB = 0 A + VAB = VOC - B IAB = 0 A RTH A + VAB = VTH - + - VTH Circuit A (Linear) B Finding VTH and RTH Two circuits are equivalent if they produce the same load voltage and current (VAB and IAB) for every possible load condition. Consider one extreme load condition: open circuit where IAB = 0 A. If the two circuits are equivalent, then VTH = Voc. ENGR-201 Thevenin's Theorem

  5. IAB = ISC A + VAB = 0 V - B ISC RTH A + VAB = 0 - + - VTH Circuit A (Linear) B Finding VTH and RTH Consider the other extreme load condition: short circuit where VAB = 0 A. If the two circuits are equivalent, then ISC = VTH/RTH RTH = VTH/ ISC ENGR-201 Thevenin's Theorem

  6. IAB RTH IAB A A IAB = ISC A + VAB - + VAB - + VAB = 0 V - VTH B B B IAB = 0 A A + - + VAB = VOC - Circuit A (Linear) Circuit A (Linear) Circuit A (Linear) B Summary: Finding VTH and RTH In summary, VTH and RTH can be found by performing two tests on a linear circuit: = Open Circuit Test: VTH = VOC Short Circuit Test: RTH = VTH/ISC Q: How practical are these two tests? ENGR-201 Thevenin's Theorem

  7. IAB IAB A A + VAB - + VAB - Circuit A (Linear) IN Circuit B Circuit B RN B B Norton’s Theorem: Finding IN and RN Using arguments similar to the ones for finding RTH an VTH, it can be shown that : IN = ISC and RN = RTH = VOC/ISC ENGR-201 Thevenin's Theorem

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