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Chapter 2.

Electrical Components and Circuits

Electric current the motion of a charge

through a medium. Electric units the unit of

charge (or quantity of electricity) C(coulomb)

? 0.001111800g of silver ion ? Charge for

reduction to silver metal. 1Faraday 9.649 x 104

coulombs 1Faraday Deposition of Ag 107.868g of

1 gram equivalent ? (6.02 x 1023 charged

particle), I dQ/dt (Q charge, A ampere)

Electrical Components

- 2A Direct-Current Circuits and Measurements
- - Direct current ??? ??? ??
- Alternating current ??? ????? ???? ?.
- 2A-1 Laws of Electricity
- ? ? ??? electrical potential (V) ??? ? ??? ??

??? 1?? ??? ????? ? ?. - V volt ? joule/conlomb (W/Q V) (IR)
- R ohm ? R? ?? O(R ?l/A) ? Ohm's

law - G ??? ??(electrical conductance) O-1, S
- I Ampere
- P Electrical power. joules/sec, W
- P dw/dt VdQ/dt VI
- P (IR)I I2R. joule's law

Kirchhoff's Laws - Current low the algebraic

sum of currents around any point in a circuit is

zero. -Voltage low the algebraic sum of the

voltages around a closed electrical loop is

zero.

Power Law P IV P I2R V2/R

2A-2 Direct-Current Circuits

- Series circuits

Fig 2-1. A battery, a switch, three resistors

in series.

? ? D?? kirchhoff's law ?? I4 - I3 0 or I4

I3 , I3 I2 at point C. the current is the

same at all points I I1 I2 I3 I4 ?

Voltage low V - V3 - V2 - V1 0 or V V1

V2 V3 by ohm's law V 1(R1 R2 R3)

IReq ? Req R1 R2 R3 IR1 V1 , V2

IR2 , V3 IR3

V1 I1 R1 IR1

(2-9)

Voltage dividers Fig 2-3 a ? series connection

of resistor ? discrete increment

- Potentiometer continuously variable

2) Parallel Circuits Resistors in parallel at

point A

Kirchhoff's current law to point A I1 I2

I3 - It 0 It I1 I2 I3

- Parallel resistances create a current divider.

I1 V/R1 1/R1 G1 Rp

G1 --- ----- ----- --- or I1 It ---

It --- It V/Rp 1/Rp Gp

R1 Gp

(Ex. 2-1)

Calculate a) the total resistance, b) the

current from the battery, c) the current present

in each of the resistors, and d) the potential

drop across each of the resistors.

- 1 1 1
- ( --- --- ) ---
- R2 R3 R2,3
- 1 1 1 3
- --- --- --- --- R2,3 13.3O
- R 20 40 40

V

15 b) The current V IR I --- -----

0.67A

Rs 22.3 c) V V1 V2 V3 V1 I1R1

6.03 I I2 I3 ??? 9.0

V1 15 x ------------ 6.0V

(9.0 13.3)

13.3 V2 V3 V2,3 15 x ------ 9.0V

22.3 d) R1?? I1 I

0.67A I2 9.0/20 0.45A I3 9.0/40

0.22A

2A-3 Direct Current, Voltage, and Resistance

Measurements

Digital Volmeters and Multimeters DArsonval

moving-coil meter ? Digital

Voltmeters and Multimeters. Power Source,

display, A/D converter

The Loading Error in Potential Measurements

The Loading Error in Current Measurements

See equations 2-19 and 2-20

2B Alternating current Circuits

Alternating voltage and current ??? ?? ??? ???

???? ??? ??? ?? ???? ?? ?? ??. ( the simplest

alternating waveform is sine-wave volt or

current.) - Period (Tp) The time required for

the completion of one cycle - Cycle one complete

revolution - Frequency(f) HZ time number of

cycles per second

f 1/tp (2-21)

Sinusoidal signals

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2B-1 Sinusoidal Signals

The AC produced by rotation of a coil in a

magnetic field. A pure sine wave ? ??? ???? ??

??(????) IP? vector? ??. (??? Ip amplitude.)

?? t ?? 2p radian ? ??? ?? ? ? ? 2p/tp 2pf

Any time t?? instantaneous value ? Vpsin

?t Vp maximum or peak voltage the amplitude

?? ?? ? Ip sin ?t Ip sin 2pft ?? ??

v Vp sin ?t Vp sin 2pft Out of phase by

90o Phase difference phase angle(f) ??? ? Ip

sin(?t f) Ip sin(2pft f)

(rms current voltage) DC, AC? ???? ? ??? ??

???? ???? Joule heat DC the effective value of

a sinusoidal, current Report, heating effect of

AC is calculated by averaging I2R losses even

complete cycle

1 Hz ?? ?? ??? ??? ?? ohm??

square wave ??? 1.00 ??? 1.00 sine

wave ??? 1.11 ??? 1.41 ??? ???

1.15 ??? 1.73

2B-2 Reactance in Electrical Circuits

Reactance - capacitance capacitor

inductance inductor Use ? converting

alternating current to DC or the converse

? discriminating among signals of different

frequencies or separating ac dc

signals. Capacitors ?? a pair of conductors

separated by a thin layer of a dielectric

substance

Position 1

Position 2

Figure 2-8. (a) A series RC circuit. Time

response of circuit when switch S is (b) in

position 1 and (c) in position 2.

2B-3 Capacitors and Capacitance 1) Capacitance ?

a momentary current ? current ceases ? to be

changed ? switch? 2? discharge. Capacitor ? ?

? ???? switch off ?? ??? ?? The quantity of

electricity Q ? ? ??, ??, ??, ??? ? ????? ?? ??

1 Faraday 1 V? ???? ?? ???? ??? ??? ??? 1 C? ??

capacitance. ( µF, PF)

V 1/C ?idt 1/C? Ip sin wt dt

-1/wc Ip cos wt 1/wc Ip

sin(wt - p/2) ? Vp 1/wc Ip,

V (1/wc) I 1/wc Xc ?

capacitive reactance ?? O

Xc -1/wc, V XcI

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Rate of current changes in an RC circuit By

Kirchhoff ? voltage law

Vi Vc VR

Vi constant

Vi q/C iR

Rate of Voltage Change in an RC circuit

use Ohms law to eq. 2-35

Phase relations between current and voltage in an

RC circuit

Rate of Current Potential Change across RL

circuit. RC circuit? ??? ???? ??

VR Vi( I - e-tR/L )

VL Vi e-tR/L

L/R time constant

2B-4 Response of Series RC Circuits to Sinusoidal

Inputs Response of series RC RL circuits to

sinusoidal inputs signal (Vs)

Ip

(1/?C Xc)

At sufficiently high frequencies capacitance, f

become negligible I v are in phase. 1/?C? ??

R? ?? ?? ?. ? ??? ? ?? At very low

frequencies, the phase angle p/2

Voltage, current and phase Relationships for

series RL circuit

Figure 2-9

Capacitive Inductive Reactance impedance

Xc 1/wC 1/2pfC

XL wL

2pfL Impedance Z ?????? ??? ??? ??? ?(????? ???

??) At, RC circuit

Z vR2 Xc2

Z vR2 XL2

Ip Vp/Z

??? ??? ? frequency dependent ? current?

voltage ??? phase difference

Figure 2-10

ltVector diagrams for Reactive Circuitsgt V? ???

90??. at capacitance V? ??? 90???. at

inductance Z vR2 (XL - Xc)2 Z vR2 Xc2 ,

f -arctan Xc/R Z vR2 XL2 , f -arctan

XL/R Z vR2 (XL Xc)2 f -arctan (XL Xc) /

R (XL gt Xc ? ??) ex) ? peak current ?

voltage drop Z v(50)2 (40 - 20)2 53.8O Ip

10 v/53.8 0.186A Vc 0.186 x 20

3.7V VR 0.186 x 50 9.3V VL 0.186 x

40 7.4V

2B-5 Filters Based on RC Circuits High-pass

Low-Pass Filters RC RL circuits ? low f

component? ??? ?? high-f signals? ??? ?? filter?

?? (low pass filter) or ?? ??. ? RC circuit??

high-pass filter Vo across the resistor R

(a) high pass filter and (b)low-Pass Filters

Low pass filter

2B-6 The Response of RC Circuits to Pulsed

Inputs ltResonant Circuitsgt impedance Z? ?? ? XL

Xc ? ? ?? I E/Z E/R ? the condition

of Resonance resonant frequency fo 1/2pfoC

2pfoL ? fo 1/2pvLC ex) (Vp)i 15.0 V (peak

voltage), L 100mH, R 20O, C 1.200µF.

Figure 2-13

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2B-7 Alternating Current, Voltage, and Impedance

Measurements Parallel Resonance Filters

Xc XL fo 1/2pvLC Z of the

parallel circuit Z

vR2 (XLXc/Xc-XL)2 At parallel circuit at

resonance ? Z? ?? ? maximum voltage drop ? ?

tank circuit Behavior of RC Circuits with

pulsed inputs RC ??? pulse ? ? various form

(with of pulse time const) ??? ??? ?? Simple

Electrical Measurements Galvanometers ? DC? ??,

?? ?? ?? the current in duceol motion of a coil

suspended in a yixed magnetic yiedd. ? D'arsonval

movement or coil. He Ayrton Shunt to vary the

range of a galvanometers p29. ?? ?? ?

measurement of current and voltage.

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Semiconductor Device

- 2C Semiconductors and Semiconductor Devices
- Semiconductors
- Electronic circuits contain one or more nonlinear

devices such as transistors, semiconductor

diodes, and vacuum or gas-filled tubes. - Nonlinear components rectification (from ac to

dc ) amplitude modulation or frequency modulation

vacuum tube ? Semiconductor based diodes and

transistors ? integrated circuits (Tr, R, C

conductor) - -Semiconductor ?? low cost, low power

consumption, small heat generation, long life and

compactness.

- 2C-1 Properties of silicon germanium

semiconductors. - Sufficient thermal agitation occurs at room temp.

to liberate an occasional electron from its

bonded state, leaving it free to more through the

crystal lattice and thus to conduct electricity. - Hole positively charged region.
- -Electron negatively charged region.
- -Hole electron ? ???? ??.
- -Doping of arsenic or antimony (Group ?) ? n type
- of indium or gallium (Group ?) ? p

type - Positive holes are less mobile them free

electrons. - Conductivity of n type gtconductivity of p type.

2C-2 . Semiconductor Diodes Pn junction motion ?

diode is a nonlinear device that has greater

conductance in one direction than in another.

Figure 2-15 A pn junction diode (c) forward -

bias (d) reverse - bias ? depletion layer ??

conductance 10-610-8

Figure 2-16 I - V cures for semiconductor Diodes

The voltage at which the sharp increase in

current occurs under reverse bias is called the

Zener breakdown voltage.

2C-3 Transistors Amplifying device -Bipolar

-Field effect transistor. ? Bipolar Tr. pnp,

npn tr.

Figure 2-17.

The mechanism of amplification with a bipolar

transistor. pnp on ? n layer 0.02mm thickness,

pgtgtn layer. (??? ??), ?The concentration of

holes in p gtgt that of electrons in n layer

Figure 2-18.

? P-type emitter junction ?? hole ?? ? ??? hole ?

very thin n-type base ? ?? - electron ? ?? (base

current IB??) ? ???? hole ? base? ?? drift ??

collector junction ?? attracting ? ??? power

supply??? ?? electron ? combined ?? ?? ??

(Ic) The no of current carrying holes is a fixed

multiple of the number of electrons supplied by

the input base current.

Field Effect Transistors (FET) FET - The

insulated gate field effect transistor.

?1091014 ? ? imput impedence ? MOSFET (metal

oxide semiconductor FET) n- chanel MOSFET The

gate is a cylindrical p-type semiconductor

surrounding a center core of n -doped material

called the channel. Two isolated n regions are

formed in a p-type substrate. ?? n.p regions ?

silicon dioxide? insulating

Figure 2-19.

(n-channel junction FET) current enhancement in

brought about by application of a positive

potential to the gate Gate ? " induce -

substrate channel below the layer of

SiO2 Depletion mode ?in the absence of a gate

voltage reverse bias is applied to the gate the

supply of electrons in the channel is depleted. ?

channel ?? ???????. The width of the reverse

biased gate junction determined (the wide of the

channel and consequently). The magnitude of the

current between source and drain.

2D Power Supplies and Regulators most ps contains

a voltage regulator.

Figure 2-20.

2D-1 Transformers VX 115 X N2/N1 N2 and N1 are

the no of turns in the secondary and primary

coils.

2D-2 Rectifiers ?Half wave rectifier ?Full wave

rectifier ?bridge rectifier ???? ? ??

Figure 2-21.

D2, D3 ? conduct on the alternate D4 and D1

conduct Since two diodes are in series with the

load, the output voltage is reduced by twice the

diode drop.

Figure 2-22.

2D-2 Rectifiers and Filters

Figure 2-23.

In order to minimize the current fluctuations. L

section filter S ? ?? C? ?? ??. ? peak to peak

ripple can be reduced.

2D-3 Voltage Regulators

Figure 2-24.

Zener diode breakdown condition ??? ??. Under

breakdown condition, a current change of 20 to 30

mA may result from a potential change of 0.1 V or

less.

2E Readout Devices

Figure 2-25. Basic analog oscilloscope component

2E-1 Oscilloscopes Cathode-Ray Tubes

Horizontal and vertical Control Plates.

Trigger Control.

Figure 2-26. Schematic of a CRT

2E-2 Recorders

Figure 2-27. Schematic of self-balancing

recording potentiometer

2E-3 Alphanumeric Displays

2E-4 Computers