Basic Circuit Concepts

Circuit Analysis Overview

Circuit Variables: v(t), i(t), q(t), f(t)

Circuit Elements: Vs, Is, R, L, C, etc.

Basic Circuit Theorems: KCL and KVL

Simple Resistive Circuits

Node Analysis Method

Mesh Analysis Method

Equivalent Circuits: Thevenin and Norton Equivalent Circuits

Impedance Matching: Maximum Power Transfer

Electrical Engineering Design Model

電路分析的應用：模型分析

Circuit whichmeets designspecifications

Laboratorymeasurements

Refinement basedon analysis

Refinement basedon measurements

Physicalinsight

CircuitCircuitanalysisanalysis

Need

Design Specifications

Concept

CircuitModel

PhysicalPrototype

Circuit Variables

Voltage

Current

公 式定 義電路變數

the energy per unit charge created by the charge separation

the rate of charge flow

-v = dw/dq

-i = dq/dt

+

-qq

1 Coulomb = charge contained in 6.24 x 1018 electrons

e- = -1.6022 x 10–19 Coulomb (C)

Ideal Basic Circuit Element

Only two terminals

Cannot be divided into other elements

+v-

1

2

i

Described mathematically by current and/or voltage

負流向：電壓從負端流進。

Tips電壓降（voltage drop）：電壓從第1點流向第2點，是由正到負。電壓升（voltage rise）：電壓從第2點流向第1點，是由負到正。正流向：電壓從正端流進。

Power and Energy

AA

vidtdq

dqdw

dtdwp === ))((

If p > 0, power is delivered to the circuit inside the box.If p < 0, power is being extracted ( generated) from the circuit inside the box.

Tips

1

2

+

-V

p=V i

+

- 1

2V

p= -V i

1

2

+

-V

p= -V i

1

2+

-V

p=V i

i i

i i

CC

BB DD

Circuit Elements

Circuit Elements電路元件

Voltage電壓源 Current電 流源

Dependent Sources Dependent SourcesIndependent SourceIndependent Source 相依型 相依型獨立型獨立型

Independent Source: Active elements

v

i

vssupplydissipate

Tips

Depending on the direction of current, an independent voltage source can supply power or dissipate power.Depending on the polarity of its terminal voltage, an independent current source can supply power or dissipate power.

v

iis

supply

dissipate

i+-

vs

+

-Vis

項目 圖 示 象限說明

電流源

電壓源

Dependent Sources: Active elements

相依型電壓電流源：依據某個電路變數而變化的

電路變數 Voltage-controlled Current-controlled

圖 示

圖 示

公 式

公式

i+-

+-V

i +-

+-V

εv= µvx =αvxis

εv= ρix = βixis

A. B.

C. D.

Electric Capacitance

電容：儲存電荷的元件

電容符號

+

-

i

V C

C (t)

C(t)

iC(t)

+

-V CC(t)

iC(t)

+

-V CC(t)

Charge on capacitorCharge on capacitor

C = q(t) = CvC(t)

A. B. C.

Current of capacitorCurrent of capacitor

iC(t) = dq(t)/dt = CdvC(t)/dt

Electric Resistance

基本電路元件：電 阻

電阻符號

i

V R

v = -iR

v = iRp = vi = (iR)i

= i2R = v2/R= v2G

v = -iRp = -vi = -(-iR)i

= i2R = v2/R= v2G

R: resistanceG: conductanceG = 1/R or R = 1/G

最常見的電阻符號

i+

-

V R

v = iR

A. B. C.

Electric Inductance

電感器：儲存磁通量(magnetic flux)的元件

電感器符號

+

-

i

V L

L(t)

L(t)

+

-

i

V L

L(t)

L(t)

A. B.

voltage of inductorvoltage of inductor

vL(t) = dψ(t)/dt = LdiL(t)/dt

Flux on inductorFlux on inductor

L = ψ(t) = LiL(t)

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