EMLAB

1

기초 회로 이론

2014. 9. 1.

EMLAB

2Contents

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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Super-computer

Rack-mount computer

motherboard

Printed circuit board

Circuits for modern electronic systems

Example : ATX power supply schematic

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4Electronic circuit design flow

System concept

Functional specification

Schematic circuit

Schematic simulation

BOM (Bill of materials)

PCB layout

Test and debugging

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5Typical electronic components

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Basic concepts

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7Charges : electrons, nucleus

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8Friction charges

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Electrons “lost”

Electrons “gained”

Contact

Separation

Generation of friction charges

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Electrons(-) are absorbed.(+) charges are generated

Electrons(-) are generated. (+) charges are absorbed.

Generation of charges : battery

e2ZnZn 2

234 HNH222NH e

Electrons are generated via electro-chemical reaction.

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The globe lights up due to the work done by electric current (moving charges).

Steady state current (simple DC circuit)

Current

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12Charge transport : microscopic view

Direction of current is de-fined as that of positive charges by convention.

Direction of current

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13

dt

dQI 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.

S

Definition of current

q

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Positive charges

Negative charges

Charge transport mechanism: drift current

Charges are drifted by electro-magnetic waves.

E

HE

H

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15Charge transport : diffusion current

Positive charges are plenty.

Charges in a wire are moved by diffusion and electromagnetic laws.

Charge movement by diffusion

Negative charges are plenty.

Diffusion

Diffusion current is due to density gradi-ent independent of charges.

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16Electromotive force

e2ZnZn 2

234 HNH222NH e

Electrons are generated via electro-chemical reaction.

Chemical battery

(reduction)

(oxidation)

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17AC(alternating current) generator

Electromotive force is generated by chang-ing magnetic flux (Faraday’s law).

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Circuit elements

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Independent sources Dependent sources

Circuit symbols

resistor capacitor inductor transformer

Ground (GND)

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20voltage sources

Voltage source

Dry cellLithium ion battery

Lead-acid battery

Switching power supply DC power supply

i-v characteristics

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21Analogy between potential energy and voltage level

• Absolute value of voltage is not impor-tant.

• Only voltage difference has physical meaning.

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• Ground (GND) is used to represent volt-age reference (0 V), arbitrarily.

Ground symbol

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current source

current sources

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24resistors

11 )()( RtitR

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25capacitors

t

0

)(1

)( dttiC

tC

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)(ti

i-v relation of a capacitor

t

0

)(1

)( dttiC

tC

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27inductors

dt

diLtL )(

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28i-v relation of an inductor

dt

diLtL )(

)(t

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29Passive sign convention

-

)(t

)(ti

A circuit element absorbs power when the current flows into the posi-tive terminal.

)()()( tittp

• For passive devices, the terminal into which current comes becomes a positive terminal.

• For independent sources, current flows out of the posi-tive terminal.

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30Example

)(ti

)(t Power is

absorbed

)(ti

)(t

Power is generated

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Power = 0.1 * 1.5 = 0.15W (absorp-tion)

1.5V

0.1A

0.1A

1.5V1.5V

-0.1A

Power = -0.1 * 1.5 = -0.15W (generation)

Example : passive sign convention

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32Power

dttitW

tittp

)()(

)()()(

Power is defined to be the energy dissipated per unit time.

)()()( titdt

dq

dq

dW

dt

dWtp

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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.

Tellegen’s theorem

-36W

54W

-18W

-36W + 54W -18W = 0

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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.

Example 1.2

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 issupplying power.

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We wish to determine the unknown voltage or current in Fig. 1.13.

Example 1.3

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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Determine the power supplied by the dependent sources in Fig. E1.4.

(a) Power supplied = 80 W;(b) power supplied = 160 W.

Example E1.4

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37Example 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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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.

Example 1.8