https___courseware.ee.calpoly.edu_~jzhang_EE112_lecture3

7/27/2019 https___courseware.ee.calpoly.edu_~jzhang_EE112_lecture3

1/5

Circuit Elements

Circuit element is a mathematical model of a

real device Active element: is capable of generating energy

Examples: generators, batteries

Passive element: absorbs (dissipates) energy

Examples: resistors, capacitors, inductors

Active Element

The most important active elements are voltageand current sources

Independent sources independent voltage source

independent current source

Dependent sources dependent voltage source

dependent current source

Active Element

Independent voltage source

provides a specified voltage

(independent of the current through the element)

v

+V

-


2/5

Active Element

Independent current sourceprovides a specified current

(independent of the voltage across the element)

i

Active Element

Dependent source

is a voltage or current generator whose source quantity

depends on another circuit variable (current or voltage)

+

-v i

dependent voltage source dependent current source

Active Element

Dependent source

There are four types of dependent sources:VCVS, VCCS, CCVS, CCCS

Vx: controlling voltage

Ix: controlling current

a,b,c,d: multiplying constants

What are the units?


3/5

+

-

+-

voltage- controlledvoltage source (VCVS)

voltage- controlledcurrent source (VCCS)

current- controlled

vol tage source (CCVS)

current- controlledcurrent source (CCCS)

v=avx i=cvx

v=bix i=dix

Example

Compute the power that is absorbed or suppliedby the element in the following network.

1 - +

2 3

36 V

Ix=4A

2A

2A

+

28V

-

+

24V

-

+ 12V -

Ix

Passive Element

Resistance is the physical ability to resistcurrent.

The circuit element used to model this behavior

is the resistor.

Circuit symbol:R

2inareasectional-cross:

inlength:

inmaterialtheofyresistivit:

mA

ml

mO

A

lR

=

Units for R:


4/5

Ohms Law

The voltage v across a resistor is directlyproportional to the current I flowing through

the resistor.

V/A1O1 =

=

iRv

ivR

+ v -

i

Ohms Law

R R

+

v

-

+

v

-

ii

v=iR v=-iR

Two possible reference choices forthe current and voltage

Conductance

Conductance is the reciprocal of resistance

Symbol: G

Units: siemens (S) or mho ( )

viRG //1 ==

Example:

Consider a 10 resistor. What is its conductance?


5/5

Power in a resistor

The powerdelivered to a resistor is

RiiiRvip

R

v

R

vvvip

2

2

)(

)(

===

===

+ v -

i

R

Example

vs

i

R=1k

Find1. G

2. i

3. p(t)

for a. vs=12 V

b. vs=10 costV

(a) A short circuit (R = 0)(b) An open circuit (R=).

Model for open and short circuit

Documents

https___courseware.ee.calpoly.edu_~jzhang_EE112_lecture3