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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 2
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
Electrical Circuits
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 3
Goal is to predict the electrical behavior of circuits, for understanding and improving their design
Voltage & Current
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 4
Voltage: Created by separation of chargesis the energy per unit chargev = dw / dq
v: voltage (V)w: energy (J)q: charge (Q)
++--
Current: Created by motion of chargesis the rate of charge flowi = dq / dt
i: current (A)t: time (s)
Power: Energy per unit timep = dw / dt = (dw / dq) * (dq/ dt)p = v.i
Lumped vs. Distributed Circuit
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 5
Majority of circuits work with
AC voltages & currents
λ: wavelength
SPACE
wavelength
Lumped vs. Distributed Circuit
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 6
Lumped circuit: Dependent variables (voltage & current) are functions of time only: λ >> l
SPACE
wavelength
Distributed circuit: Dependent variables are functions of time and space:
Lumped circuit
λ = c / f
(c: 3*108 m/s)
Example 1: lumped
f = 50 Hz
λ = 6 km!
Much larger than any circuit
Example 2: distributed
f = 100 MHz
λ = 30 cm
Comparable in size
Circu
it theo
ry
Electro
magn
etic
theo
ry
Physical circuit & Circuit model
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 7
Physical circuit is made up of electric
devices (generator, resistor, transistor,
battery, transformer, load etc..)
Circuit model consists of
interconnection of circuit elements
KIRCHHOFF`S LAWS: Reference Directions
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 8
• Direction of current flow & voltage polarity may vary with time
• Frame of reference: Assign arbitrary reference directions to current and voltage
Kirchhoff`s Voltage Law (KVL)
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 9
Datum / reference node (ground)
• 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
1
2
3
v3-2 + v2-1 + v1-3 = 0
Example: Analogy
v1-3 = 5 v climb 5 stepsv2-1 = 3 v -> e2 = 8v climb 3 more stepsv3-2 should be -8 V, so that e3=0 get back to original location:
go back 8 steps (-8 steps)
The sum of all node-node voltages = 0
for a closed node sequence (starts and ends at the same node)
Kirchhoff`s Voltage Law (KVL)
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 10
v4-5 + v2-4 + v5-2 = 0
v1-2 + v2-3 + v3-4 + v4-5 + v5=1 = 0
Circuit having 2 & 3 terminal elements
Blue closed node sequence: 2-4-5
Red closed node sequence: 1-2-3-4-5
Kirchhoff`s Current Law (KCL)
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 11
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
Surface 6:-i12 – i3 – i11 – i8 – i9 = 0
Kirchhoff`s Current Law (KCL)
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 12
Kirchhoff`s Current Law (KCL)
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 13
KVL
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 14
KVL & KCL
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 15
Power & energy
Asst. Prof. Onur Ferhanoğlu Introduction / BASICS OF ELECTRICAL CIRCUITS 16
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