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Unformatted text preview: 1 Unit 3: Other Circuit Analysis Techniques Unit 3.2 - Thevnin Equivalent Circuits Maximum Power Transfer Thevnin Equivalent Circuits f The objectives of this lecture are to: Define what is meant by an equivalent circuit. Learn how to define the two type of equivalent circuits: Thevnin equivalent circuit Norton Equivalent Circuit How to use equivalent circuits to simply the analysis of complex circuits and problems. Why are Equivalent Circuits Needed? f We have learned a number of methods and tools for analyzing electrical circuits: KVL, KCL, and Ohms Law Current and Voltage Division Node Voltage and Mesh Current Analysis Superposition Source transformation f Problems exists in analyzing circuits where part of the circuit is complex or unknown: Appliance plugged into a wall outlet. Attaching speakers to a stereo system. Speakers for a CD Player CD Reader Digital to Analog Converter Amplifier Speakers I dont care about the details of the CD player, I want to optimize the speaker design for maximum volume. Only the voltage and current at the speaker terminals are important. Importance of Equivalent Circuits f The equivalent circuit allows us to represent most of the circuit in a much simpler form f After determining the equivalent circuit, we know the current and voltage going to any load placed at that point f This allows us to do optimization, as needed, easier. Transistor Amplifier f I want to know how much power is going to resistor R5. What is important? Only the voltage and current for resistor R5 f We are not interested in the voltage and current of every element, just R5. +- R3 R5 + v 1- i 1 5000 1 v +- +- R2 + v o- i o 000 , 20 o v v s o i 40 R4 1 70 i R1 Transistor A Transistor B +- +- +- R3 R5 + v 1- i 1 5000 1 v +- +- +- +- +- R2 + v o- i o 000 , 20 o v v s o i 40 R4 1 70 i R1 Transistor A Transistor B 2 Equivalent Circuits f The goal here is to create an equivalent circuit for the complex one with the following conditions: Voltage across R5 does not change. Current to R5 does not change. f This resistor is traditionally called the LOAD Resistor. +- R3 R5 + v 1- i 1 5000 1 v +- +- R2 + v o- i o 000 , 20 o v v s o i 40 R4 1 70 i R1 Transistor A Transistor B +- +- +- R3 R5 + v 1- i 1 5000 1 v +- +- +- +- +- R2 + v o- i o 000 , 20 o v v s o i 40 R4 1 70 i R1 Transistor A Transistor B Complex Circuit I R5 +- V Thvenin Equivalent Circuit f Any linear DC circuit can be replaced by an equivalent circuit consisting of an ideal voltage source and a series resistor with appropriate values. If the complex circuit contains a dependent source, then the control voltage or current must be within that circuit....
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This note was uploaded on 08/27/2009 for the course EE 16200 taught by Professor Williamneal during the Fall '08 term at University of Texas at Austin.
- Fall '08