Unit 1.4 Circuits and Circuit Elements

# Unit 1.4 Circuits and Circuit Elements - Circuits and...

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1 1 Unit 1: Basic Circuit Theory Unit 1.4: Circuits and Circuit Elements 2 Circuits and Circuit Elements f In this lecture, you will learn about: ± Representing physical systems as circuit diagrams ± Conventional Symbols used in circuits • Ideal voltage and current sources • Resistors • Practical Voltage Source • Others • Dependent Sources 3 Physical System Example 4 Physical System Example #2 5 Schematic of Physical System 6 Schematic of Physical System

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2 7 AC and DC f DC: Direct Current ± Electrical current that flows in one direction only. f AC: Alternating Current ± Electrical current that changes (or alternates) in magnitude and direction at regular intervals. f These terms are also applied to voltages: ± DC voltage or AC voltage • Direct Current Voltage may seem weird, but that’s the way it is. f These terms are also applied to sources: ± DC current source or AC voltage source, etc. 8 EE302: DC Circuit Analysis f Nomenclature: lower case i, v denote general representations for current and voltage that may be DC and/or AC f For EE302, we will focus on DC circuits ± I (upper case) will denote currents ± V (upper case) will denote voltages 9 Types of Devices f Active Devices ± Capable of generating power ± Examples: voltage and current sources, operational amplifiers, transistors f Passive Devices ± Cannot generate power ± Examples: resistors, capacitors, inductors f For EE302, we focus on DC circuits involving resistors 10 Battery Æ Voltage Source f Source of power ± Provides voltage (12 V) ± Provides current • Varies depending what is attached to the battery + - 12 V or Circuit Symbol: + - 12 V 11 Ideal Voltage Source: Properties f If providing power to circuit, which way does the physical current flow? f Always provides the specified voltage between its terminals. f Current determined by the attached circuit. f Can supply unlimited power. + - 12 V a b I I 12 Can a voltage source absorb power?? f Battery Charger ± The battery being charged acts as a load. ± It absorbs power from the circuit.
3 13 Ideal Current Source: Properties f Always provides the specified current flowing from b to a. f Voltage between a and b can vary. f Can provide unlimited power. 2 A a b No everyday analogy for a current source. Useful to model more advanced devices. 14 Headlight f Can I represent the headlight as a voltage or current source? f No ± Gets its power from the battery ± Absorbs power all the time resistor 15 Resistor: Ohm’s Law f The current through a resistor and the voltage across it are proportional.

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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.

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Unit 1.4 Circuits and Circuit Elements - Circuits and...

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