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기초 회로 이론
2014. 9. 1.
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Contents
1. Basic concepts
2. Resistive circuits
3. Nodal and loop analysis techniques
4. Operational amplifiers
5. Additional analysis techniques
6. Capacitance and inductance
7. First and second order transient circuits
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Circuits for modern electronic systems
Rack-mount computer
Super-computer
motherboard
Printed circuit board
Example : ATX power supply schematic
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Electronic circuit design flow
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System concept
Functional specification
Schematic circuit
Schematic simulation
BOM (Bill of materials)
PCB layout
Test and debugging
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Typical electronic components
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Basic concepts
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Charges : electrons, nucleus
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Friction charges
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Generation of friction charges
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Contact
Electrons “lost”
Separation
Electrons “gained”
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Generation of charges : battery
Electrons(-) are absorbed.
(+) charges are generated
Electrons(-) are generated.
(+) charges are absorbed.
2NH 4  2e   2 NH3  H 2
Zn  Zn 2  2e 
Electrons are generated via
electro-chemical reaction.
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Current
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Steady state current (simple DC circuit)
The globe lights up due to the work done by electric current (moving charges).
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Charge transport : microscopic view
Direction of current is
defined as that of positive
charges by convention.
Direction of current
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Definition of current
S
q
I
dQ
dt
I
•
Current is electric charges in motion, and is defined as the rate of movement
of charges passing a given reference plane.
•
In the above figure, current can be measured by counting charges passing
through surface S in a unit time.
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Charge transport mechanism: drift current
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Positive charges
E
E
H
H
Charges are drifted by
electromagnetic waves.
Negative charges
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Charge transport : diffusion current
Charges in a wire are moved by diffusion and electromagnetic laws.
Positive charges are plenty.
Diffusion
Charge movement by
diffusion
Negative charges are plenty.
Diffusion current is due to density
gradient independent of charges.
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Electromotive force
Chemical battery
2NH 4  2e   2 NH3  H 2
Zn  Zn 2  2e 
(reduction)
(oxidation)
Electrons are generated via electro-chemical reaction.
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AC(alternating current) generator
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Electromotive force is generated by
changing magnetic flux (Faraday’s law).
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Circuit elements
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Circuit symbols
Independent sources
resistor
Dependent sources
capacitor
Ground (GND)
inductor
transformer
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voltage sources
Dry cell
Lithium ion battery
Lead-acid battery
Switching power supply
DC power supply
Voltage source
i-v characteristics
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Analogy between potential energy and voltage level
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• Absolute value of voltage is not important.
• Only voltage difference has physical
meaning.
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Ground symbol
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• Ground (GND) is used to represent
voltage reference (0 V), arbitrarily.
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current sources
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current source
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resistors
 R (t )  i1 (t )  R1
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capacitors
1
C (t ) 
C
t
 i (t ) dt
0
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i-v relation of a capacitor
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t
1
C (t )   i (t ) dt
C0
i (t )
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inductors
 L (t )  L
di
dt
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i-v relation of an inductor
 L (t )  L
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di
dt
 (t )
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Passive sign convention
p (t )   (t )  i (t )
i (t )

 (t )
-
A circuit element absorbs power
when the current flows into the
positive terminal.
• For passive devices, the terminal into which current
comes becomes a positive terminal.
• For independent sources, current flows out of the
positive terminal.
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Example
i (t )
Power is
generated

 (t )

i (t )

 (t )

Power is
absorbed
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Example : passive sign convention
1.5V
0.1A
-0.1A
1.5V
Power = -0.1 * 1.5 = -0.15W (generation)
0.1A
1.5V
Power = 0.1 * 1.5 = 0.15W (absorption)
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Power
Power is defined to be the energy dissipated per unit time.
p (t ) 
dW
dW dq


  (t )  i (t )
dt
dq dt
p (t )   (t )  i (t )
W    (t )  i (t )dt
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Tellegen’s theorem
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• The sum of the powers absorbed by all elements in an electrical
network is zero.
• Another statement of this theorem is that the power supplied in a
network is exactly equal to the power absorbed.
54W
-18W
-36W
-36W + 54W -18W = 0
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Example 1.2
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Given the two diagrams shown in Fig. 1.12, determine whether the element is
absorbing or supplying power and how much.
In Fig. 1.12a the power is P=(2 V)(–4 A)=–8 W. Therefore, the element is
supplying power.
In Fig. 1.12b, the power is P=(2 V)(–2 A)=–4 W. Therefore, the element is
supplying power.
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Example 1.3
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We wish to determine the unknown voltage or current in Fig. 1.13.
In Fig. 1.13a, a power of –20 W indicates that the element is delivering power.
Therefore, the current enters the negative terminal (terminal A), and from Eq. (1.3)
the voltage is 4 V. Thus, B is the positive terminal, A is the negative terminal, and
the voltage between them is 4 V.
In Fig 1.13b, a power of ±40 W indicates that the element is absorbing power and,
therefore, the current should enter the positive terminal B. The current thus has a
value of –8 A, as shown in the figure.
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Example E1.4
Determine the power supplied by the dependent sources in Fig. E1.4.
(a) Power supplied = 80 W;
(b) power supplied = 160 W.
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Example 1.7
Use Tellegen’s theorem to find the current Io in the network in Fig. 1.19.
-12 + 6Io - 108 - 30 - 32 + 176 = 0
Io = 1A
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Example 1.8
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The charge that enters the BOX is shown in Fig. 1.20. Calculate and sketch the
current flowing into and the power absorbed by the BOX between 0 and 10
milliseconds.
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