EE 2006 Electrc Crcut Analyss Fall 2014 September 04, 2014 Lecture 02 1
For Your Informaton Course Webpage http://www.d.umn.edu/~jngba/electrc_crcut_analyss_(ee_2006).html You can fnd on the webpage: Lecture: course syllabus, lecture notes, homework (& solutons) Lab: lab syllabus (lab report format, gradng matrx), lab nstructons (11 labs) Tutorals: breadboard, resstor color code, Pspce (download ste and tutoral) For unt conerson, you can learn more at http://physcs.nst.go/cuu/unts/unts.html 2
Lab 1 Dgtal Multmeter Lab nstructons Aalable onlne Prnt out and read before Lab MWAH 391, 4:00 7:00 pm, next Monday or Wednesday (Sept 8/10) Work n pars (group of 3 f odd number) Group data, nddual report Lab safety rules 3
Lecture Outlne Voltage, power, and energy Acte and passe elements Ohm s Law Krchhoff s current and oltage laws 4
Reew: Electrc Current Created by moton of charge I Measured by charge change rate, unt n A (amperes) = dq dt, 1A = 1C 1s Conenton on drecton: flow drecton of poste charges, opposte to the flow of negate charges 5
Reew: DC Current and AC current Drect current (DC) Alternatng current (AC) I DC ( I ): current that remans constant wth tme AC ( ): current that ares snusodally wth tme 6
Voltage Defnton: electrcal potental dfference between two ponts of an electrc crcut or electromote force (emf) requred to moe the charge from one pont to another pont a ab b The potental dfference between ponts a and b: ab = a b = dw/dq, w: energy wth unt n joules (J) q: charge wth unt n coulombs (C) : oltage wth unt n olts (V) 1V=1J/C Polarty: or used to defne the reference drecton Voltage drop drecton: from polarty to polarty The polarty can be defned by you 7
Power and Energy Power: the tme rate of expendng or absorbng energy, measured n watts (W): p=dw/dt=(dw/dq).(dq/dt)= Sgn conenton: a b Current drecton s the same as the oltage drop drecton, P= When current drecton s opposte to the oltage drop drecton, P= a b 8
Crcut Elements Crcut element s a mathematcal model of a real dece Acte element: p = <0, generatng energy.e., batteres, generators, operatonal amplfers Passe element: p=>0, absorbng or storng energy.e., resstors (absorbng energy), capactors and nductors (storng energy) 9
Acte Element The most mportant acte elements are oltage and current sources Independent sources Dependent sources V Independent oltage sources Independent current sources Dependent oltage source, VCVS or CCVS Dependent current source, VCCS or CCCS 10
Example of Dependent Sources A B A 10 C 5V C 0.2 CCVS CCCS 11
Resstance Resstance s the physcal ablty to resst current. The crcut element used to model ths behaor s the resstor, whch s a passe element Crcut symbol: R Unt for R: Ω, 1Ω =1V/A A: crosssectonal area n m 2 l: length n m Resstance s dependent on the materal property and physcal dmensons of the resstor ρ: Materal receptty n Ω m A R l = ρ 12
Ohm s Law Statement: the oltage across a resstor s drectly proportonal to the current flowng through the resstor,.e., = R V = R 13
Short Crcut and Open Crcut = R ( 0 R < ) (A)Short Crcut (SC) R = 0 = 0 (B) Open Crcut (OC) R = = 0 =0 R=0 =0 R = 14
Conductance Conductance G s the recprocal of resstance R,.e., G = 1 = R Unt of G: semens (S) or mhos ( ) 1S=1/Ω=1A/V 15
Power Power: the tme rate of expendng or absorbng energy, measured n watts (W): p=dw/dt=(dw/dq).(dq/dt)= Instantaneous power for any crcut element: p(t)=(t)(t) The power delered to a resstor s p p = = = = R ( R) = = 2 2 R R = = 2 G 2 G 16
Branch, Nodes and Loops One node A branch s a sngle element such as a oltage (current) source or a resstor; A node s the pont of connecton between two or more branches; A loop s any closed path n a crcut 17
Elements n Seral and Parallel Two elements are n seres f they exclusely share a sngle node Two elements are n parallel f they are connected to the same two nodes 18