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CHAPTERS 2 & 3
NETWORKS 1:
0909201-01
17 September 2002 – Lecture 2b
ROWAN UNIVERSITY
College of Engineering
Professor Peter Mark Jansson, PP PE
DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING
Autumn Semester 2002
networks I
Announcements –

Homework 1 answers posted today
 Returned next Monday



Homework 2 is posted on web
First Test is in 1 week  Ch. 3: 24 Sep
Lab 1 assignment is due in 1 week
 Sec 1: 23 Sep
 Sec 2: 24 Sep
networks I
Today’s Learning Objectives –



Define open and short circuit elements
Analyze independent electrical sources
Analyze dependent sources
 VCVS, VCCS, CCVS, CCCS


Analyze DC circuits with passive and active
elements including: resistance and power
sources
Introduce Kirchhoff’s Laws
chapter 2 - overview
engineering and linear models - done
active and passive circuit elements -done
resistors – Ohm’s Law - done
independent sources
dependent sources
transducers
switches
open & short circuits
Open - a break in the circuit where no
current flows.
Short - a connector between two elements
with no voltage drop.
open
i(t) = 0
v(t)  0
(if there is a source in the circuit)
short
v(t) = 0
i(t)  0
(if there is a source
in the circuit)
sources
A “thing” that can supply energy.

The energy can come in the form of:
 current
 voltage
 power?
There are two types of sources:


Independent - constant no matter what you hook it to.
Dependent - the value is tied to some other point in the
circuit.
ideal independent sources
Ideal independent sources maintain their
assigned value indefinitely.
i(t)
An ideal voltage
+ v(t) source will maintain
–
its voltage value and
Voltage
source
+
v(t)
–
An ideal current
i(t) source will maintain
its current value and
sustain ANY value of
sustain ANY value of
current.
voltage.
Current
source
sources / series connections
series – elements connected in series
have the same current running through
them
10
+
_
V= 5v
+
_
+
i
20
_
sources / parallel connections
parallel – elements connected in
parallel have the same voltage
i1
i2
i3
+
I
R1
R2
R3
v
_
ideal dependent sources
Voltage and current sources can be
controlled by either a voltage or a current
somewhere else in the circuit.
voltage sources
+
–
current sources
vd = r ic
id = g vc
or
or
vd = b vc
id = d ic
r, b, g and d are the gains of these sources
the key dependent sources
CCVS:
VCVS:
VCCS:
CCCS:
current-controlled voltage source
voltage-controlled voltage source
voltage-controlled current source
current-controlled current source
examples
CCCS: exercise 2.8-1
VCCS: exercise 2.8-2
CCVS: exercise 2.8-3
a very important example
c
b
c
ic
ic
+
b
vbe
+
–
vbe
–
ic =
rp
gmvbe
e
e
transducers
devices that convert physical quantities
into electrical quantities:



pressure
temperature
position - potentiometer
switches
Make before break
SPST
SPDT
SPDT
ch. 1 & 2 important concepts
Circuits; current; voltage; power
Passive sign convention
Active and Passive elements
Linearity - superposition + homogeneity
Resistors and Ohm’s Law
Sources - Ideal, independent and dependent
Opens and Shorts
Switches
WHAT DO YOU KNOW (or,
what’s going to be on the
test)?
Homework for next Monday
9.23
show all work for any credit
Dorf & Svoboda, pp. 58-63
Problems 2.3-1, 2.3-2, 2.3-6, 2.4-1,
2.5-1, 2.5-3, 2.5-5, 2.5-7, 2.6-1, 2.6-2,
2.7-1
Verification Problem 2-2
Design Problem 2-1
chapter 3 - overview
electric circuit applications
define: node, closed path, loop
Kirchoff’s Current Law
Kirchoff’s Voltage Law
a voltage divider circuit
parallel resistors and current division
series V-sources / parallel I-sources
resistive circuit analysis
electric circuit applications
electric telegraph
transatlantic cable
engineers vs. scientists
those who can do, those who can’t
teach?
resistive circuits
we are ready to make working circuits
with resistive elements and both
independent and dependent sources.
words we know: short, open, resistor
new words:



node
closed path
loop
more definitions
node: a junction where two or more
are connected
closed path: a traversal through a
series of nodes ending at the starting
node
loop:
an illustration
R1
NODE
V
+
–
PATH OR LOOP
R2
ARE THESE TWO NODES OR ONE NODE?
Gustav Robert Kirchhoff
1824-1887
two laws in 1847
how old was he?
Kirchhoff’s laws
Kirchhoff’s Current Law (KCL): at
any instant is zero.
Kirchhoff’s Voltage Law (KVL):

The algebraic sum of the voltages around
any closed path in a circuit is zero for all
time.
KCL
R1=10
Node 1
Node 2
+
_
+
+
_
_
I=5A
R3= 5
R2= 20
Node 3
Assume passive sign convention
Node 1
I=5A
R1=10
i1
+ v1=50v _
Node 2
+
+
I
v2=20v
R2= 20
Node 1 +I - i1 = 0
Node 2 +i1 - i2 - i3 = 0
Node 3 +i2 + i3 - I = 0
i2 = v2/R2
i3 = v3/R3
i2
_
R3= 5
v3=20v
_
i3
Node 3
Use KCL and
Ohm’s Law
KVL
R1=10
_
+
+
V= 5v
+
_
Start
+V - vR1 - vR2 = 0
iV = iR1 = iR2 = i
+V = iR1 + iR2
V = i(R1 + R2)
LOOP 1
R2= 20 _
i = V/(R1 + R2)
vR! = iR1 = VR1 /(R1 + R2)
vR2 = iR2 = VR2/(R1 + R2)
SERIES RESISTORS
R =10
1
_
+
+
V= 5v
+
_
Start
LOOP 1
R2= 20 _
NOTE
+V - vR1 - vR2 = 0
i = V/(R1 + R2)
iV = iR1 = iR2 = i
vR! = iR1 = VR1 /(R1 + R2)
+V = iR1 + iR2
vR2 = iR2 = VR2/(R1 + R2)
V = i(R1 + R2)
VOLTAGE DIVIDER
SERIES RESISTORS
resistors attached in a “string” can be
added together to get an equivalent
resistance.
R = 2
R = 3
R = 9
R = 4
One Minute Paper
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