silde bài giảng: mạch điện tử 1

Chöông 1 1

KYÙ HIEÄU

Giaù trò taïi tónh ñieåm Q (quiescent-point): IEQ, VCEQ

Giaù trò moät chieàu (DC): I

E, VCE

Toång giaù trò töùc thôøi: i

E, vCE

Giaù trò töùc thôøi cuûa thaønh phaàn thay ñoåi theo thôøi gian: i

e, vce

E

E

e i

I

 i

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Chöông 1

2

CHÖÔNG 1: DIODE BAÙN DAÃN

1.1 Giôùi thieâu

1.2 Vaät lieäu baùn daãn

1.3 Diode baùn daãn thoâng thöôøng

1.4 Chænh löu

1.5 Phaân tích maïch Diode

1.6 Maïch xeùn (Clippers) vaø maïch ghim ñieän aùp (Clampers)

1.7 Diode Zener

1.8 Caùc loaïi Diode khaùc

1.9 Aûnh höôûng cuûa nhieät ñoä vaø caùc thoâng soá kyõ thuaät

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1.1 GIÔÙI THIEÄU

x Diode laø moät linh kieän ñieän töû phi tuyeán ñôn giaûn nhaát.

x Caùc loaïi diode: Diode chaân khoâng, Diode khí, Diode chænh löu

kim loaïi, Diode baùn daãn, vv.

x Diode baùn daãn: Caáu taïo vaø tính chaát.

Phöông phaùp phaân tích maïch.

ÖÙng duïng.

1.2 VAÄT LIEÄU BAÙN DAÃN

Caùc vaät lieäu baùn daãn thöôøng duøng:

x Silicon (Si)

x Germanium (Ge)

x Gallium Arsenide (GaAs)

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Chöông 1

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1.2.1 Caáu truùc nguyeân töû vaø caáu truùc tinh theå

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Chöông 1

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1.2.2 Söï daãn ñieän

x Caùc möùc naêng löôïng

x Söï daãn ñieän trong chaát baùn daãn

Doøng khueách taùn (diffusion current): Khi coù söï thay ñoåi maät ñoä electron (hole)

Doøng chaûy (drift current): Khi coù ñieän tröôøng ngoaøi

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1.2.3 Baùn daãn loaïi p vaø baùn daãn loaïi n

x “Doping”: Laø quaù trình ñöa vaøo chaát baùn daãn caùc chaát khaùc caàn thieát.

x Baùn daãn loaïi p

9 Chaát ñöa vaøo: Chaát nhaän (acceptor material). Ví duï: Boron (III)

9 Caáu truùc tinh theå vaø sô ñoà möùc naêng löôïng

9 Phaàn töû mang ñieän chuû yeáu: Loã troáng (positive): p-type material

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x Baùn daãn loaïi n

9 Chaát ñöa vaøo: Chaát cho (donor material). Ví duï: Phosphorus (V)

9 Caáu truùc tinh theå vaø sô ñoà möùc naêng löôïng

9 Phaàn töû mang ñieän chuû yeáu: Electron (negative): n-type material

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1.3 DIODE BAÙN DAÃN THOÂNG THÖÔØNG

1.3.1 Caáu truùc cuûa Diode baùn daãn

x Caáu truùc vaø kyù hieäu

x Lôùp tieáp xuùc pn (pn junction)

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x Söï phaân cöïc cuûa Diode (bias)

1.3.2 Quan heä giöõa doøng ñieän vaø ñieän aùp cuûa Diode

x Diode lyù töôûng

9

vi > 0: i

D > 0 vaø v

D = 0 (Diode ngaén maïch: short circuit)

9

vi < 0: v

D < 0 vaø i

D = 0 (Diode hôû maïch: open circuit)

vi

ri

v

D

iD

+

_

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Chöông 1 10

x Ñaëc tuyeán Volt-Ampere (VA) cuûa Diode

(



1

)

(



1

)

T

D

D

mV

v

o

mkT

qv

D

o i I

e

I

e

Io: Doøng phaân cöïc nghòch baõo hoøa

(reverse saturation current), A

q = 1,6E-19 C

k = 1,38E-23 J/ oK: Haèng soá

Boltzmann

T: Nhieät ñoä tuyeät ñoái,

o

K

m: 1

d m

d 2: Haèng soá thöïc nghieäm

q

k

T

VT

| 25 mV, taïi nhieät ñoä phoøng

(27

oC)

9 Phaân cöïc thuaän (v

D > 0): Khi

D mVT

v !! : T

D

mV

v

D

o i |

I

e

9 Phaân cöïc nghòch (v

D < 0): Khi

D mVT

v !! : D

o i |



I

T

D

mV

v

o

I

e

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Chöông 1 11

x Diode thöïc teá vaø Xaáp xæ tuyeán tính hoùa töøng ñoaïn (piecewise￾linear approximation)

1.3.3 Maïch ñieän töông ñöông cuûa Diode

<Xem Giaùo trình vaø TLTK [3]>

1.3.4 Caùc phöông phaùp phaân tích maïch duøng Diode

<Xem Giaùo trình vaø TLTK [3]>

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Chöông 1 12

1.4 CHÆNH LÖU (Rectification)

Chænh löu laø quaù trình chuyeån ñoåi töø tín hieäu xoay chieàu (ac) thaønh tín

hieäu moät chieàu (dc).

Löu yù: Caùc ví duï trong phaàn naøy söû duïng ñaëc tuyeán Diode lyù töôûng.

1.4.1 Chænh löu baùn soùng (Half-wave rectification)

1

9

x Ñònh luaät Kirchhoff veà ñieän aùp (KVL):

i L

i D

D

r

R

v

v i 



vi > 0: v

D = 0 (Diode ngaén maïch),

i L

i D

r

R

v i 

,

i L

i L

L

L

D

r

R

v

R

v

R i 

vi < 0: Diode hôû maïch: iD

0,

D

0

L

L

v

R i

vi = Vimcos(

Z

ot)

ri v

D iD

v

L

R

L

+

_

_

+

Ideal diode

N

guoàn (Source) Taûi (Load)

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Chöông 1 13

x Ñieän aùp treân taûi v

L (Chænh löu baùn soùng):

x Phaân tích tín hieäu chænh löu baùn soùng:

Giaù trò trung bình:

S

Lm

T

L dc

L

V

v

t dt

T

V

³

(

)

1 ,

Khai trieån Fourier: ¸

¹

· ¨

©

§





 cos

4

 ...

15

2

cos

2

3

2

cos

2

1

1

v

(

t

)

V

t

t

t

L Lm

o

o

Zo

S

Z

S

Z

S

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Chöông 1 14

x Loïc (filter) tín hieäu chænh löu baùn soùng:

9 Maïch loïc duøng ñeå loïc boû caùc haøi xoay chieàu (harmonics) nhaèm giöõ

laïi thaønh phaàn moät chieàu cuûa tín hieäu v

L(t): Loïc thoâng thaáp (lowpass

filter – LPF).

9 Caùc daïng maïch loïc cô baûn:

R

R

R

C

L L

C

C

C

(a) (b) (c)

9 Giaû söû duøng maïch loïc (a) vôùi RC = 100/

Z

o vaø R >> R

L.

Bieân ñoä ñieän aùp ngoõ ra cuûa maïch loïc taïi taàn soá n

Z

o (n

t1) laø:

n

V

n RC

V

V Ln

o

Ln

on 100

1

2

|



Z

vôùi VLn laø bieân ñoä ñieän aùp ngoõ vaøo cuûa maïch loïc taïi taàn soá n

Z

o.

Söû duïng nguyeân lyù choàng chaäp, ñieän aùp ngoõ ra:

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Chöông 1 15

¸

¹

· ¨

©

§

|





 sin

4

 ...

3000

1 sin

2

300

1 sin

200

1

1

v

(

t

)

V

t

t

t

o Lm

o

o

Zo

S

Z

S

Z

S

9 Ñoä gôïn soùng (Ripple factor):

Thaønh phaàn DC:

S

Lm

L dc

V

V ,

Thaønh phaàn gôïn soùng: ¸

¹

· ¨

©

§

 sin

2



...

300

1 sin

200

1

v

V

t

t

r Lm

o

Zo

S

Z

Giaù trò hieäu duïng (rms) cuûa thaønh phaàn gôïn soùng:

> @ 280 ...

(300

)

1

(200

)

1

2

(

)

1

(

)

2

2

1/ 2

2 Lm Lm

T

r rms

r

V

V

v

t dt

T

v ¸ 



|

¹

· ¨

©

§

¿

¾

½

¯

®

­

{

³

S

Ñoä gôïn soùng

0.011

280

(

)

,

{

|

S

L dc

r rms

V

v

“Nothing is difficult to those who have the will.”

- Dutch Poet's Society

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