BASICS OF ELECTRICAL CIRCUITS
EHB 211 E
Introduction
Asst. Prof. Onur Ferhanoğlu
1
BASICS OF ELECTRICAL CIRCUITS
Time: Monday: 09:30 – 12: 30
Place: Room 5301
Grading: Midterm 1 (20%)
Midterm 2 (20%)
HW1-4 (5% * 4 = 20 %)
Final
(40%)
Web: http://web.itu.edu.tr/~ferhanoglu/teaching.htm
References:
• Leon O. Chua, Charles A. Desoer, Ernest S. Kuh, ”Linear and
Nonlinear Circuits,” McGraw-Hill, 1987.
• Prof. Müştak E. Yalçın’s notes
• Norman Balabanian, “Electric Circuits,” McGraw-Hill, 1993.
• J.W. Nillson, S. Riedel, “Electric Circuits,” Prentice Hall, 2010.
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
Lecture 1: Intro & KVL + KCL
Lecture 2: Graph theory
Lecture 3: Two-terminal resistors
Lecture 4: Simple resistive circuits
MIDTERM 1
Lecture 5: Techniques of circuit analysis
Lecture 6: Multiterminal resistors
Lecture 7: Operational amplifiers
Lecture 8: Superposition theorem
MIDTERM 2
Lecture 9: Thevenin & Norton circuits
Lecture 10: First order circuits
Lecture 11: Second order circuits
Lecture 12: State-Space Equations
FINAL
2
Electrical Circuits
Goal is to predict the electrical behavior of circuits, for understanding and improving their design
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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Voltage & Current
Voltage: Created by separation of charges
is the energy per unit charge
v = dw / dq
v: voltage (V)
w: energy (J)
q: charge (Q)
++
--
Current: Created by motion of charges
is the rate of charge flow
i = dq / dt
i: current (A)
t: time (s)
Power: Energy per unit time
p = dw / dt = (dw / dq) * (dq/ dt)
p = v.i
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
4
Lumped vs. Distributed Circuit
Majority of circuits work with
AC voltages & currents
λ: wavelength
wavelength
SPACE
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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Lumped vs. Distributed Circuit
Lumped circuit: Dependent variables (voltage & current) are functions of time only: λ >> l
Distributed circuit: Dependent variables are functions of time and space:
λ=c/f
(c: 3*108 m/s)
wavelength
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
Example 2: distributed
f = 100 MHz
λ = 30 cm
Comparable in size
Electromagnetic
theory
Lumped circuit
Circuit theory
SPACE
Example 1: lumped
f = 50 Hz
λ = 6 km!
Much larger than any circuit
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Physical circuit & Circuit model
Physical circuit is made up of electric
devices (generator, resistor, transistor,
battery, transformer, load etc..)
Circuit model consists of
interconnection of circuit elements
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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KIRCHHOFF`S LAWS: Reference Directions
• Direction of current flow & voltage polarity may vary with time
• Frame of reference: Assign arbitrary reference directions to current and voltage
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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Kirchhoff`s Voltage Law (KVL)
• n-node circuit
• n-1 node-datum voltages
(e1,e2,…,en)
• en = 0 V
• + / - : voltage reference
directions
• vk-j = ek – ej = vk-n - vj-n
Datum / reference node (ground)
2
v3-2 + v2-1 + v1-3 = 0
1
The sum of all node-node voltages = 0
for a closed node sequence (starts and ends at the same node)
Example:
3
Asst. Prof. Onur Ferhanoğlu
v1-3 = 5 v
v2-1 = 3 v -> e2 = 8v
v3-2 should be -8 V, so that e3=0
Introduction / BASICS OF ELECTRICAL CIRCUITS
Analogy
climb 5 steps
climb 3 more steps
get back to original location:
go back 8 steps (-8 steps)
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Kirchhoff`s Voltage Law (KVL)
Circuit having 2 & 3 terminal elements
Blue closed node sequence: 2-4-5
v4-5 + v2-4 + v5-2 = 0
Red closed node sequence: 1-2-3-4-5
v1-2 + v2-3 + v3-4 + v4-5 + v5=1 = 0
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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Kirchhoff`s Current Law (KCL)
For all Gaussian (closed) surfaces, sum of all currents leaving the surface = 0
-> electric charge is conserved
Circuit with 2 terminal elements (capacitors, batteries, resistors)
and a 3 terminal element (operational amplifier)
Gaussian surface
Surface 1:
i1 + i2 = 0
Surface 2:
-i1 + i12 = 0
Surface 3:
i1 + i4 + i5 + i6 = 0
Surface 4:
i3 + i11 + i8 + i9 – i6 – i5 – i4 = 0
Surface 5:
i11 - i10 – i4 - i7 = 0
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
Surface 6:
-i12 – i3 – i11 – i8 – i9 = 0
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Kirchhoff`s Current Law (KCL)
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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Kirchhoff`s Current Law (KCL)
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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KVL
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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KVL & KCL
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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Power & energy
Asst. Prof. Onur Ferhanoğlu
Introduction / BASICS OF ELECTRICAL CIRCUITS
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