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Lesson 13: Maximum Power Transfer Theorem

Lesson 13: Maximum Power Transfer Theorem. Learning Objectives. Analyze complex series-parallel circuits using thevenin ’ s theorem. Apply the Maximum Power Transfer theorem to solve appropriate problems. MAX POWER TRANSFER.

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Lesson 13: Maximum Power Transfer Theorem

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  1. Lesson 13: Maximum Power Transfer Theorem

  2. Learning Objectives • Analyze complex series-parallel circuits using thevenin’s theorem. • Apply the Maximum Power Transfer theorem to solve appropriate problems.

  3. MAX POWER TRANSFER In someapplications, thepurpose of a circuitistoprovidemaximumpowerto a load. Someexamples: • Stereoamplifiers • Radio transmitters • Communicationsequipment Ourquestionis: Ifyouhave a system, what load shouldyouconnecttothesystem in orderthatthe load receivesthemaximumpowerthatthesystem can deliver?

  4. How might we determine RLD such that PLD is maximized? Maximizing PLD

  5. Maximum power is transferred to the load when the load resistance equals the Thévenin resistance as seen from the load (RLD = RTh). When RLD = RTh, the source and load are said to be matched. Maximum power transfer theorem

  6. As RLD increases, a higher percentage of the total power is dissipated in the load resistor. But since the total resistance is increasing, the total current is dropping, and a point is reached where the total power dissipated by the entire circuit starts dropping. Maximizing PLD

  7. Maximum power • The power delivered when RLD = RTh is • BE CAREFUL!!! Note that this is not true if RLD  RTh

  8. MAXIMUM POWER TRANSFER THEOREM • The total power delivered by a supply such as ETh is absorbed by both the Thévenin equivalent resistance and the load resistance. Any power delivered by the source that does not get to the load is lost to the Thévenin resistance.

  9. Example Problem 1 Find the Thévenin equivalent circuit to the left of terminals a-b. Calculate the maximum power transfer to the load if RLD=RTH Determine the power dissipated by RLD for load resistances of 2 and 6.

  10. When maximum power is delivered to RLD, the efficiency is a mere 50%. Efficiency

  11. Efficiency • Communication Circuits and Amplifiers: • Max Power Transfer Is More Desirable Than High Efficiency • Power Transmission (115 VAC 60 Hz Power ): • High Efficiency Is More Desirable Than Max Power Transfer • Load Resistance Kept Much Larger Than Internal Resistance Of Voltage Source

  12. Example Problem 2 Find the value of R so that RLD=RTH Calculate the maximum power dissipated by RLD

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