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ECE 4991 Electrical and Electronic Circuits Chapter 2

ECE 4991 Electrical and Electronic Circuits Chapter 2. Hitchhikers Guide to the Galaxy. Chapter 2 - The basic concepts and practice at analyzing simple electric circuits with sources and resistors Chapter 3 – More harder networks to analyze and the notion of equivalent circuits

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ECE 4991 Electrical and Electronic Circuits Chapter 2

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  1. ECE 4991 Electrical and Electronic CircuitsChapter 2

  2. Hitchhikers Guide to the Galaxy • Chapter 2 - The basic concepts and practice at analyzing simple electric circuits with sources and resistors • Chapter 3 – More harder networks to analyze and the notion of equivalent circuits • Chapter 4 – Capacitors and inductors added to the mix • Chapter 5 – Analyzing transient situations in complex passive networks • Chapter 8 – New subject – the wonders of operational amplifiers as system elements • Chapter 9 – Introduction to semiconductors – the basics and diodes – more network analysis • Chapter 10 – Bipolar junction transistors and how they work – now you can build your own op amp

  3. What’s Important in Chapter 2 • Definitions • KCL & applications • KVL & applications • Electric power / power ratings • Ohm’s Law • Equivalent resistance computation • Voltage Dividers / Current Dividers • Ideal v real voltage sources

  4. 1. Definitions • Voltage • Current • Charge • Power • Energy • Network • Branch • Node • Loop • Mesh

  5. 2. KCL & Applications • First, note that for current to flow, there must be a closed circuit • Kirchhoff’s Current Law (KCL)  in = 0

  6. 2. Applying KCL • Find nodes • Label currents • Write node equations

  7. 2 ½ . Current Speed • Metals are seas of electrons – each atom gives up an electron which can move and be part of the current • i = dq/dt = charge density/length of wire * carrier velocity • Therefore carrier velocity = v = i / charge density • Charge density = e * ~3x1023/m3 = ~5x104 Coul/m3 • For a 1 amp current, v = ~ 2x10-5 m/s = ~ .02 mm/s !

  8. 3. KVL & Applications • First, note that for KVL to work, there must be a closed circuit • Kirchhoff’s Voltage Law (KVL) vn = 0

  9. 3. Applying KVL • Label voltages • Pick loops • Write loop equations

  10. 4. Electric Power / Power Ratings • Power is work done per unit time • For an electronic element, Power is the product of the voltage across the element and the current flowing through it P = VI • “Positive Power” is dissipated by a load • “Negative Power” is provided by an energy source

  11. 4 ½. I-V Characteristics i v

  12. 5. Ohm’s Law • A resistor is a passive electronic circuit element with the following property – the voltage developed across it is directly proportional to the electric current through it V = IR • R is measured in volts per amp • 1 volt/amp = 1 ohm (Ω) • What are some ways to calculate the power dissipated in resistor R?

  13. 5. Working with Ohm’s Law

  14. 6. Equivalent Resistance Computation

  15. 6. Equivalent R • For series resistors Req =  Ri • For parallel resistors 1 / Req =  1/Ri

  16. 6. Equivalent R Practice

  17. 7. Voltage & Current Dividers • A voltage divider accesses a fraction of a voltage • A current divider accesses a fraction of a current

  18. I I 8. Ideal v Real Sources • Ideal sources are independent of loading • Real sources have equivalent series or parallel internal resistances

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