giao trinh linh kien dien tu gtvt

GIO TRNH LINH KIN IN T

Page 1

CHNG I. LINH KIN TH NG

Trng thi in ca mi linh kin in t c c trng bi 2 thng s:

in p u v cng dng in i. Mi quan h tng h i=f(u) c biu din

bi c tuyn Volt-Ampere.

Ngi ta c th phn chia cc linh kin in t theo hm quan h trn l

tuyn tnh hay phi tuyn. Nu hm i=f(u) l tuyn tnh (hm i s bc nht hay

phng trnh vi phn, tch phn tuyn tnh), phn t c gi l phn t tuyn

tnh (R, L, C) v c th p dng c nguyn l xp chng.

in tr: uR

i .1

T in:dt

duCi .

Cun dy: dtuLi .

1

Nu hm i=f(u) l quan h phi tuyn (phng trnh i s bc cao, phng

trnh vi phn hay tch phn phi tuyn), phn t c gi l phn t phi tuyn

(diode, Transistor).

2.1. in tr (Resistor)

Nh cp trong chng trc, dng in l dng chuyn di c hng

ca cc ht mang in v trong vt dn cc ht mang in l cc electron t

do. Cc electron t do c kh nng dch chuyn c do tc ng ca in p

ngun v trong qu trnh dch chuyn cc electron t do va chm vi cc nguyn

t nt mng v cc electron khc nn b mt mt phn nng lng di dng

nhit. S va chm ny cn tr s chuyn ng ca cc electron t do v c

c trng bi gi tr in tr.

2.1.1. nh ngha: in tr l linh kin cn tr dng in, gi tr in tr cng

ln dng in trong mch cng nh.

nh lut Ohm: Cng dng in trong mch thun tr t l thun

vi in p cp v t l nghch vi in tr ca mch.


Page 2

R

EI

[E]: Volt (V)

[I]: Ampere (A)

[R]: Ohm ()

2.1.2. Cc thng s ca in tr

a. Gi tr in tr

Gi tr in tr c trng cho kh nng cn tr dng in ca in tr.

Yu cu c bn i vi gi tr in tr l t thay i theo nhit , m v

thi gian,in tr dn in cng tt th gi tr ca n cng nh v ngc li.

Gi tr in tr c tnh theo n v Ohm (), k, M, hoc G.

Gi tr in tr ph thuc vo vt liu cn in, kch thc ca in tr v

nhit ca mi trng.

S

lR .

Trong : : in tr sut [m]

l: chiu di dy dn [m]

S: tit din dy dn [m2]

Trong thc t in tr c sn xut vi mt s thang gi tr xc nh. Khi

tnh ton l thuyt thit k mch, cn chn thang in tr gn nht vi gi tr

c tnh.

b. Sai s

Sai s l chnh lch tng i gia gi tr thc t ca in tr v gi tr

danh nh, c tnh theo %

%100

dd

ddtt

R

RR


Page 3

Trong : Rtt: Gi tr thc t ca in tr

Rdd: Gi tr danh nh ca in tr

c. H s nhit in tr (TCR-Temperature Co-efficient of Resistor):

TCR l s thay i tng i ca gi tr in tr khi nhit thay i 1oC,

c tnh theo phn triu

)/(10./ 6 CppmR

TR o (parts per million)

Khi nhit tng, s lng cc electron bt ra khi qu o chuyn ng

tng v va chm vi cc electron t do lm tng kh nng cn tr dng in ca

vt dn. Trong hu ht cc cht dn in khi nhit tng th gi tr in tr

tng, h s 0 (PTC: Positive Temperature Co-efficient). i vi cc cht bn

dn, khi nhit tng s lng electron bt ra khi nguyn t tr thnh

electron t do c gia tng t ngt, tuy s va chm trong mng tinh th cng

tng nhng khng ng k so vi s gia tng s lng ht dn, lm cho kh nng

dn in ca vt liu tng, hay gi tr in tr gim, do c h s 0 (NTC:

Negative Temperature Coefficient). H s nhit 0 cng nh, n nh ca

gi tr in tr cng cao.

Ti mt nhit xc nh c h s nhit xc nh, gi s ti nhit T1

in tr c gi tr l R1 v h s nhit l 1 , gi tr in tr ti nhit T2:

12112 1 TTRR

H s gc=T

R

0oK

Hnh 2.1. nh hng ca nhit ti gi tr in tr ca vt dn


Page 4

d.Cng sut ti a cho php

Khi c dng in cng I chy qua in tr R, nng lng nhit ta ra

trn R vi cng sut: RIIUP .. 2

Nu dng in c cng cng ln th nhit lng tiu th trn R cng

ln lm cho in tr cng nng, do cn thit k in tr c kch thc ln

c th tn nhit tt.

Cng sut ti a cho php l cng sut nhit ln nht m in tr c th

chu c nu qu ngng in tr b nng ln v c th b chy. Cng sut

ti a cho php c trng cho kh nng chu nhit.

RIR

UP .2max

2max

max

Trong cc mch thc t, ti khi ngun cp, cng dng in mnh nn

cc in tr c kch thc ln. Ti khi x l tn hiu, cng dng in yu

nn cc in tr c kch thc nh do ch phi chu cng sut nhit thp.

2.1.3. Phn loi v k hiu in tr

a. in tr c gi tr xc nh

in tr than p (in tr hp cht Cacbon): c ch to bng cch

trn bt than vi vt liu cn in, sau c nung nng ha th rn, nn thnh

dng hnh tr v c bo v bng lp v giy ph gm hay lp sn.

Hp cht Carbon

Cc in cc

Dy dn Dy dn

Hnh 2.2. in tr than p


Page 5

in tr than p c di gi tr tng i rng (t1 n 100M), cng sut

danh nh (1/8W-2W), nhng phn ln c cng sut l 1/4W hoc 1/2W. Mt

u im ni bt ca in tr than p chnh l c tnh thun tr nn c s

dng nhiu trong phm vi tn s thp (trong cc b x l tn hiu m tn).

in tr dy qun c ch to bng cch qun mt on dy khng

phi l cht dn in tt (Nichrome) quanh mt li hnh tr. Tr khng ph

thuc vo vt liu dy dn, ng knh v di ca dy dn. in tr dy qun

c gi tr nh, chnh xc cao v c cng sut nhit ln. Tuy nhin nhc im

ca in tr dy qun l n c tnh cht in cm nn khng c s dng trong

cc mch cao tn m c ng dng nhiu trong cc mch m tn.

in tr mng mng: c sn xut bng cch lng ng Cacbon, kim

loi hoc oxide kim loi di dng mng mng trn li hnh tr. in tr mng

mng c gi tr t thp n trung bnh, v c th thy r mt u im ni bt ca

in tr mng mng l tnh cht thun tr nn c s dng trong phm vi

tn s cao, tuy nhin c cng sut nhit thp v gi thnh cao.

Nichrome

Li cch in

Dy dn

Dy dn

Hnh 2.3. in tr dy qun

Mng mng

Dy dn Dy dn

Hnh 2.4. in tr mng mng


Page 6

b. in tr c gi tr thay i

Bin tr (Variable Resistor) c cu to gm mt in tr mng than

hoc dy qun c dng hnh cung, c trc xoay gia ni vi con trt. Con

trt tip xc ng vi vi vnh in tr to nn cc th 3, nn khi con trt

dch chuyn in tr gia cc th 3 v 1 trong 2 cc cn li c th thay i. C

th c loi bin tr tuyn tnh (gi tr in tr thay i tuyn tnh theo gc xoay)

hoc bin tr phi tuyn (gi tr in tr thay i theo hm logarit theo gc xoay).

Bin tr c s dng iu khin in p (potentiometer: chit p) hoc iu

khin cng dng in (Rheostat)

in tr nhit (Thermal Resistor -Thermistor):

L linh kin c gi tr in tr thay i theo nhit . C 2 loi nhit tr:

Nhit tr c h s nhit m: Gi tr in tr gim khi nhit tng (NTC),

thng thng cc cht bn dn c h s nhit m do khi nhit tng cung cp

nng lng cho cc electron nhy t vng ha tr ln vng dn nn s lng

ht dn tng ng k, ngoi ra tc dch chuyn ca ht dn cng tng nn gi

tr in tr gim

Nhit tr c h s nhit dng: Gi tr in tr tng khi nhit tng, cc

nhit tr c lm bng kim loi c h s nhit dng (PTC) do khi nhit

Vnh in tr

Trc iu khin

Con

trt

1 3

2

Rheostat

VR

1 3

2

potentiometer

VR

Hnh 2.5. Bin tr (VR)


Page 7

tng, cc nguyn t nt mng dao ng mnh lm cn tr qu trnh di chuyn

ca electron nn gi tr in tr tng.

Nhit tr c s dng iu khin cng dng in, o hoc iu

khin nhit : n nh nhit cho cc tng khuch i, c bit l tng khuch

i cng sut hoc l linh kin cm bin trong cc h thng t ng iu khin

theo nhit .

in tr quang (Photo Resistor)

Quang tr l linh kin nhy cm vi bc x in t quanh ph nh sng

nhn thy. Quang tr c gi tr in tr thay i ph thuc vo cng nh

sng chiu vo n. Cng nh sng cng mnh th gi tr in tr cng gim

v ngc li.

Khi b che ti: MnknR .100.

Khi c chiu sng: knnR .100.

Quang tr thng c s dng trong cc mch t ng iu khin bng

nh sng:(Pht hin ngi vo ca t ng; iu chnh sng, nt

Camera; T ng bt n khi tri ti; iu chnh nt ca LCD;)

2.1.4. Cch ghi v c cc tham s in tr

a. Biu din trc tip

Ch ci u tin v cc ch s biu din gi tr ca in tr: R(E) ;

K - K ; M - M ;

Ch ci th hai biu din dung sai:

V d: 8K2J: R=8,2K; =5%

R=8,2K 41,0 K=7,79K8,61K

F=1% J=5%

G=2% K=10%

H=2,5% M=20%


Page 8

Hoc c th cc ch s biu din gi tr ca in tr v ch ci biu

din dung sai. Khi ch s cui cng biu din s ch s 0 (bc ca ly tha

10).

V d: 4703G: R=470K ; =2%

b. Biu din bng cc vch mu

i vi cc in tr c kch thc nh khng th ghi trc tip cc thng s

khi ngi ta thng v cc vng mu ln thn in tr.

3 vng mu:

2 vng u biu din 2 ch s c ngha thc

Vng th 3 biu din s ch s 0 (bc ca ly tha 10)

Sai s =20%

4 vng mu



Vng th 4 biu din dung sai (trng nh)

5 vng mu:



Vng th 5 biu din dung sai (trng nh)

Bng quy c m vch mu

Mu Tr s Sai s

en 0

Nu 1 1%

2 2%

Cam 3

Vng 4

Lc 5

Lam 6


Page 9

2.1.5. ng dng

in tr c s dng trong cc mch phn p phn cc cho

Transistor m bo cho mch khuch i hoc dao ng hot ng vi hiu sut

cao nht.

in tr ng vai tr l phn t hn dng trnh cho cc linh kin b ph

hng do cng dng qu ln. Mt v d in hnh l trong mch khuch i,

nu khng c in tr th Transistor chu dng mt chiu c cng tng i

ln.

c s dng ch to cc dng c sinh hot (bn l, bp in hay

bng n,) hoc cc thit b trong cng nghip (thit b sy, si,) do in

tr c c im tiu hao nng lng di dng nhit.

Xc nh hng s thi gian: Trong mt s mch to xung, in tr c

s dng xc nh hng s thi gian.

Phi hp tr khng: tn hao trn ng truyn l nh nht cn thc

hin phi hp tr khng gia ngun tn hiu v u vo ca b khuch i, gia

u ra ca b khuch i v ti, hay gia u ra ca tng khuch i trc v

u vo ca tng khuch i sau.

2.2. T in

2.2.1. nh ngha

T in gm 2 bn cc lm bng cht dn in c t song song vi

nhau, gia l lp cch in gi l cht in mi (giy tm du, mica, hay gm,

Tm 7

Xm 8

Trng 9

Vng kim -1 5%

Bc kim -2 10%

Vch 2 Vch 4

Vch 5

Vch 3

Vch 1

Bn cc

kim loi

Lp in mi

(khng kh)


Page 10

khng kh). Cht cch in c ly lm tn gi cho t in (t giy, t du, t

gm hay t khng kh).

Nu in tr tiu th in nng v chuyn thnh nhit nng th t in tch

nng lng di dng nng lng in trng, sau nng lng c gii

phng. iu ny c th hin c tnh tch v phng in ca t in.

2.2.2. Cc tham s ca t in

a. in dung ca t in

Gi tr in dung c trng cho kh nng tch ly nng lng ca t in.

d

SC o

Trong : : H s in mi ca cht cch in

o=8,85.10-12

(F/m): Hng s in mi ca chn khng

S: Din tch hiu dng ca 2 bn cc

d: Khong cch gia 2 bn cc

in dung c n v l F, tuy nhin trong thc t 1F l gi tr rt ln nn

thng s dng cc n v khc: 1F=10-6F; 1nF=10-9F; 1pF=10-12F

Mt s h s in mi thng dng:

Chn khng =1

Khng kh =1,0006

Gm =30-7500

Mica =5,5

Du =4

Giy kh =2,2

Polystyrene =2,6

K hiu

C


Page 11

b. Sai s: L chnh lch tng i gia gi tr in dung thc t v gi

tr danh nh ca t in, c tnh theo %

dd

ddtt

C

CC

Ctt: in dung thc t

Cdd: in dung danh nh

Ty theo yu cu ca mch m dung sai ca t in c gi tr ln hay nh.

c. Tr khng ca t in

Tr khng ca t in c trng cho kh nng cn tr dng in xoay chiu

ca t in

cc XjfCj

Z .2

1

fCX c

2

1 : dung khng ca t

cZf :0 : h mch i vi thnh phn mt chiu

0: cZf : ngn mch i vi thnh phn xoay chiu

d. H s nhit ca t in (TCC Temperature Co-efficient of Capacitor)

L thay i tng i ca gi tr in dung khi nhit thay i 1oC,

c tnh theo o/oo:

)/(106 CppmC

TC

TCC o

TCC cng nh th gi tr in dung cng n nh, do mi loi t ch hot

ng trong mt di nhit nht nh.

(a) C=200pF vi cht in mi l khng kh (b) C=1,5F vi cht in mi l gm

Gm


Page 12

e. in p nh thng

Khi t vo 2 bn cc ca t in p mt chiu, sinh ra mt in trng

gia 2 bn cc. in p cng ln th cng in trng cng ln, do cc

electron c kh nng bt ra khi nguyn t tr thnh cc electron t do, gy nn

dng r. Nu in p qu ln, cng dng r tng, lm mt tnh cht cch

in ca cht in mi, ngi ta gi l hin tng t b nh thng. in p

mt chiu t vo t khi gi l in p nh thng.

Khi s dng t cn chn t c in p nh thng ln hn in p t vo

t vi ln. in p nh thng ph thuc vo tnh cht v b dy ca lp in

mi. Cc t c in p nh thng ln thng l cc t c kch thc ln v cht

in mi tt (Mica hoc Gm).

f. Dng in r

Thc t trong cht in mi vn tn ti dng in c cng rt nh,

c gi l dng r, khi c th coi t in tng ng vi mt in tr c

gi tr rt ln, c M.

2.2.3. Phn loi v k hiu

a.T c in dung xc nh

T in c phn chia thnh 2 dng chnh: T khng phn cc (khng c

cc tnh) v t phn cc hoc cng c th phn loi theo cht in mi.

T giy ( Paper Capacitors): T giy l t khng phn cc gm cc l

kim loi xen k vi cc lp giy tm du c cun li theo dng hnh tr. in

dung C=1nF0,1F, in p nh thng ca t giy c khong vi trm Volt.

Hot ng trong di trung tn.

K hiu:

Dng r

dt

duCi


Page 13

T gm (Ceramic Capacitors): T gm l t khng phn cc c sn

xut bng cch lng ng mng kim loi mng trn 2 mt ca a gm hoc cng

c th mt trong v mt ngoi ca ng hnh tr, hai in cc c gn vi

mng kim loi v c bc trong v cht do. in dung thay i trong phm vi

rng C=n.pF0,5F, in p nh thng c khong vi trm Volt. Hot ng

trong di cao tn (dn tn hiu cao tn xung t), c c im l tiu th t nng

lng.

K hiu:

T Mica (Mica Capacitors): T Mica l t khng phn cc c ch

to bng cch t xen k cc l kim loi vi cc lp Mica (hoc cng c th lng

ng mng kim loi ln cc lp Mica tng h s phm cht). in dung

C=n.pF0,1F, in p nh thng vi nghn Volt. n nh cao, dng r

thp, sai s nh, tiu hao nng lng khng ng k, hot ng trong di cao tn

(c s dng trong my thu pht sng Radio).

K hiu:

Lp in mi L kim loi

L kim

loi

Bn cc kim loi

Bn cc kim loi

Lp in mi (gia cc bn cc)

C

C

C


Page 14

T mng mng (Plastic film Capacitors): L t khng phn cc,

c ch to theo phng php ging t giy, cht in mi l Polyester,

Polyethylene hoc Polystyrene c tnh mm do. in dung C=50pF-n.10F

(thng thng: 1nF-10F), in p nh thng c khong vi nghn Volt, hot

ng trong cc di tn audio (m tn) v radio (cao tn).

K hiu:

T in phn (Electrolytic Capacitors): T in phn cn c gi l

t oxi ha (hay t ha), y l loi t phn cc, gm cc l nhm c cch ly

bi dung dch in phn v c cun li thnh dng hnh tr. Khi t in p

mt chiu ln hai bn cc ca t in, xut hin mng oxide kim loi cch in

ng vai tr l lp in mi. T in phn c in dung ln, mng oxit kim loi

cng mng th gi tr in dung cng ln (0,1F n.1000F), in p nh thng

thp (vi trm Volt), hot ng trong di m tn, dung sai ln, kch thc tng

ln v gi thnh thp.

K hiu:

+ _

C


Page 15

T Tantal: T Tantal cng l t phn cc trong Tantal c s dng

thay cho Nhm. T Tantal cng c gi tr in dung ln (0,1F-100F) nhng

kch thc nh, dung sai nh, tin cy v hiu sut cao, in p nh thng vi

trm Volt. Thng c s dng trong cc mc ch qun s, trong cc mch

m tn v trong cc mch s.

K hiu:

b. T xoay (Air-Varialbe Capacitors )

C th thay i gi tr in dung ca t in bng cch thay i din tch

hiu dng gia 2 bn cc hoc thay i khong cch gia 2 bn cc

T xoay: gm cc l ng v l tnh c t xen k vi nhau, hnh

thnh nn bn cc ng v bn cc tnh. Khi cc l ng xoay lm thay i din

tch hiu dng gia 2 bn cc do thay i gi tr in dung ca t. Gi tr in

dung ca t xoay ph thuc vo s lng cc l kim loi v khong khng gian

gia cc l kim loi (Gi tr cc i: 50F-1000F v gi tr cc tiu: n.pF).

in p nh thng cc i c vi kV. T xoay l loi t khng phn cc v

thng c s dng trong my thu Radio chn tn

K hiu:

T vi chnh (Trimmer): Khc vi t xoay l iu chnh din tch hiu

dng gia cc bn cc, t vi chnh c th thay i gi tr bng cch thay i

khong cch gia cc bn cc. T vi chnh gm cc l kim loi c t xen k

C

Cc l tnh

Cc l ng

Trc iu khin


Page 16

vi nhau, gia l lp in mi, khong cch gia cc bn cc c thay i

nh c vit iu chnh.

Thng thng t vi chnh c ni song song vi t xoay tng kh nng

iu chnh. Gi tr in dung C (n.pF-200pF), in p nh thng trung bnh,

hiu sut cao (tn hao nng lng thp). T vi chnh cng l t khng phn cc.

T ng trc chnh: T ng trc gm 2 ng hnh tr kim loi c

bc lp nha lng vo nhau. Lp nha ng vai tr l lp in mi. ng ngoi

c nh ng vai tr l bn cc tnh, ng bn trong c th trt ng vai tr l

bn cc ng, do din tch hiu dng gia 2 bn cc c th thay i lm thay

i in dung ca t. Gi tr in dung (C=n.pF-100pF), c ng dng trong

di cao tn.

2.2.4. Cch ghi v c tham s ca t in

a. Ghi trc tip: i vi cc t c kch thc ln (T ha, T tantal) c th

ghi trc tip cc thng s trn thn ca t

Gi tr in dung

in p nh thng

Vit iu chnh

Bn cc trn

Bn cc di

Lp in mi

Hnh 2.T vi chnh

ng c nh

(bn ngoi)

Lp in mi

ng trt

(bn trong)

Hnh 2. T ng trc chnh

in cc


Page 17

b. Ghi theo quy c

3 ch s v 1 ch ci:

n v l pF

2 ch s u c ngha thc

Ch s th 3 biu din bc ca ly tha 10

Ch ci biu din sai s

V d:

0.047/200V: C=0,047F; UBR=200V

2.2/35: C=2,2F; UBR=35V

102J: C=10.102pF=1nF; =5%

.22K:C=0,22F; =10%

Bng ngha ca ch s th 3 Sai s

2.2.5. ng dng

Dung khng ca t:

Ch s H s nhn

0 100

1 101

2 102

3 103

4 104

5 105

8 10-2

9 10-1

B=0,1% H=3%

C=0,25% J=5%

D (E)=0,5% K=10%

F=1% M=20%

G=2% N=0,05%


Page 18

fCX c

2

1

Nhn xt: Dung khng ca t t l nghch vi tn s f ca dng in. Tn s

cng cao th dung khng ca t cng nh v ngc li. Vy c th ni, t c tc

dng chn thnh phn mt chiu ( cXf ;0 ) v dn tn hiu cao tn. Da

vo tnh cht m t in c ng dng trong cc mch:

T ghp tng: Ngn thnh phn mt chiu m ch cho thnh phn

xoay chiu qua, cch ly cc tng v thnh phn mt chiu, m bo iu kin

hot ng c lp ca tng tng trong ch mt chiu. i vi tn hiu cao tn

c th s dng t phn cc hoc t khng phn cc, tuy nhin i vi tn hiu

tn s thp phi s dng t phn cc (T ha, t Tantal c in dung ln).

T thot: Loi b tn hiu khng hu ch xung t (tp m)

T lc: c s dng trong cc mch lc (thng cao, thng thp,

thng di hoc chn di) (Kt hp vi t in hoc cun dy to ra mch lc

th ng).

T cng hng: Dng trong cc mch cng hng LC chn tn

Ngoi ra t cn c tnh cht tch v phng in nn c s dng trong cc

mch chnh lu l phng in p mt chiu.

2.3. Cun cm

2.3.1. nh ngha v k hiu

Cun dy l mt dy dn c bc lp sn cch in qun nhiu vng lin

tip trn li st. Li ca cun dy c th l: Li khng kh, li st bi hay li st

l

2.3.2. c tnh ca cun dy

a. To t trng bng dng in

Li khng kh Li st l Li st bi


Page 19

Khi cho dng in mt chiu qua cun dy, dng in s to nn t trng

u trong li cun dy (c xc nh theo quy tc vn nt chai).

Cng t trng: Il

nH [A/m]

n: S vng dy

l: Chiu di ca li [m]

I: cng dng in [A]

Cng t cm: HB o [T] (Tesla)

o: t thm ca chn khng o=4.10-7

(H/m)

: t thm tng i ca vt liu t so vi chn

khng

Nu cng dng in I khng i th H v B l t trng u

Nu cng dng in i thay i th H v B l t trng bin thin

b. To dng in bng t trng

Hin tng cm ng in t

nh lut Faraday: Nu t thng qua mt cun dy bin thin s sinh

ra trong cun dy mt sc in ng cm ng c ln t l vi tc bin

thin ca t thng.

nh lut Lentz: Sc in ng cm ng sinh ra dng in cm ng c

chiu chng li s bin thin ca t thng sinh ra n.

Sc in ng cm ng:t

necu

.


Page 20

n : s vng dy

: lng t thng bin thin qua cun dy

t : khong thi gian bin thin

Hin tng t cm:

Nu dng in qua mt cun dy bin thin s sinh ra mt sc in

ng t cm trong lng cun dy chng li s bin thin ca dng in sinh ra

n v c ln t l vi tc bin thin ca dng in.

Sc in ng t cm: t

iLetc

. (L: H s t cm [H])

Hin tng h cm:

Khi c hai cun dy c qun chung trn mt li hoc c t gn

nhau, khi dng in bin thin cun ny sinh in p h cm cun kia.

Sc in ng h cm: t

iMehc

(M: H s h cm)

2.3.3. Cc tham s ca cun cm

a. H s t cm L

c trng cho kh nng cm ng

ca cun dy

inL

= S

l

no

2

.

b.Tr khng ca cun dy

Trong thc t lun tn ti in tr thun R bn trong cun dy

fLjRZ LL 2

Cm khng ca cun dy:

fLX L 2


Page 21

RL R , tn hao trn cun dy cng nh, dy cun l kim loi dn in

tt.

d. Tn s lm vic gii hn ca cun dy

Do cc vng dy c cch ly vi nhau bi lp cch in nn tn ti t

in k sinh trong cun dy, trong min tn s thp c th b qua nh hng ca

in dung k sinh nhng trong min tn s cao cun dy tng ng vi mt

mch cng hng song song.

Tn s cng hng:

LCfo

2

1

Nu f>fo, cun dy mang tnh dung nhiu hn tnh cm, nn fo c gi l

tn s lm vic gii hn ca cun dy.

2.3.4. Phn loi v ng dng

a. Theo li cun dy

Cun dy li khng kh (air-core coils)

Cun dy c li bng nha, g hay vt liu khng t tnh. Cun dy

li khng kh c h s t cm nh (


Page 22

tiu hao nng lng in di dng nhit nn cun dy li khng kh c hiu

sut cao.

Cun dy li st bi

C li l bt st nguyn cht trn vi cht dnh khng t tnh. Cun

dy li st bi c h s t cm ln hn so vi cun dy li khng kh ph thuc

vo t l pha trn. Thng c s dng khu vc tn s cao v trung tn

Cun dy li st l

t thm ca li st t ln hn rt nhiu so vi t thm ca st

bi nn cun dy li st t c h s t cm ln, thng c ng dng trong

min tn s thp (m tn).

b.Theo ng dng: Cun lc, cun cng hng hay cun chn.

Ngoi ra trong thc t cun dy cn c ng dng trong lnh vc

truyn v tuyn, Relay in t hoc my pht in,

2.4. My bin p

2.4.1. nh ngha v k hiu

My bin p c s dng tng hoc gim in p ca ngun xoay chiu

m vn gi nguyn tn s.

Bin p gm hai hay nhiu cun dy trng sn cch in c qun chung trn

mt li. Li ca my bin p c th l st l, st ferit hay li khng kh.

Cun dy c ni vi ngun cp c gi l cun s cp, cun dy c

ni vi ti c gi l cun s cp.

K hiu:

Li st l Li st bi Li khng kh

Cun s cp Cun th cp Cun s cp Cun th cp

Cun s cp

Cun th cp


Page 23

Trong thc t tit kim ngi ta c th ch cn s dng mt cun dy

c gi l bin p t ngu, tuy nhin gia cun s cp v th cp khng c

cch ly v in.

Nguyn l:

Khi cho ngun in xoay chiu qua cun s cp, dng in bin thin sinh

ra t trng bin i v c cm ng sang cun th cp sinh ra sc in ng

cm ng e2, mt khc trn cun s cp cng xut hin sc in ng cm ng e1

Cun s cp: t

ne

.11

Cun th cp: t

ne

.22

Trong : n1, n2 ln lt l s vng dy ca cun s cp v cun th cp.

2.4.2. Cc t l ca bin p

T l v in p: 2

1

2

1

2

1

n

n

e

e

u

u

T l v dng in: 1

2

2

1

n

n

i

i

T l v cng sut

Cng sut tiu th cun s cp:

111 .iuP

Cng sut tiu th cun th cp:

222 .iuP


Page 24

Mt bin p l tng coi nh khng c s tiu hao nng lng trn hai

cun dy s cp, th cp v mch t nn khi : P1=P2

Tuy nhin mt my bin p thc t lun c cng cun th cp nh hn

cng sut ca cun s cp do cun s cp v th cp c in tr thun tiu hao

nng lng di dng nhit ngoi ra dng in Foucault xut hin trong li t

cng tiu hao mt phn nng lng.

Hiu sut ca my bin p:

%100.1

2

P

P

)%9080(max

tng hiu sut ca my bin p cn phi gim tn hao bng cch s

dng cc l st mng trng sn cch in, dy qun c tit din ln v ghp cht.

T l v tng tr: 2

2

1

2

1

n

n

R

R

2.4.3. Phn loi v ng dng ca my bin p

Bin p ngun: Cp in p xoay chiu cho cc mch in v in t, c

th c kch thc t nh ti ln, c s dng trong cc trm bin p, ng thi

c tc dng cch ly cc linh kin vi ngun cao p.

Bin p cao tn: c s dng trong cc b thu pht sng Radio, li c th

l li st bi hoc li khng kh, tuy nhin nhc im ca li khng kh l phn

ln cc ng cm ng t u i ra ngoi, iu ny nh hng n c tnh ca

my bin p.

Bin p m tn: Di tn lm vic (20Hz-20kHz), thc hin phi hp tr

khng (ti thiu ha thnh phn in cm trong mch), tuy nhin kch thc v

trng lng ln nn ngy cng t c s dng.


Page 25

CHNG II. CC LINH KIN TCH CC

I. Cht bn dn (Semiconductor)

1.1.1. Cu trc vng nng lng ca cht rn tinh th

Trong mng tinh th ca cht rn, ty theo cc mc nng lng m cc

in t c th chim ch hay khng chim ch, ngi ta phn bit ba vng nng

lng khc nhau:

Vng ha tr (vng y): Tt c cc mc nng lng u b in t

chim ch, khng c mc nng lng t do.

Vng dn (vng trng): Cc mc nng lng u cn trng hoc c th b

chim ch mt phn.

Vng cm: Trong khng tn ti mc nng lng no in t c th

chim ch hay xc sut tm ht ti y bng 0.

Ty theo v tr tng i gia 3 vng trn, cc cht rn c chia lm 3

loi (xt ti 0oK).

Nng lng vng cm: g c vE E E

Trong Ec: Nng lng y vng dn

Ev: Nng lng nh vng ha tr

to dng in trong cht rn cn phi thc hin 2 qu trnh: qu trnh

to ht dn t do nh nng lng kch thch v qu trnh chuyn ng c hng

ca cc ht mang in di tc dng ca in trng.

2gE eV : Cht cch in 0 2eV Eg eV : Cht bn dn 0Eg eV : Cht dn in

Vng dn

Vng ha tr

Vng cm Vng dn

Vng ha tr

Vng cm Vng dn Ev

Ec

Eg Ev

Ec Eg

Hnh 1. Phn loi cht rn theo cu trc vng nng lng

Vng ha tr


Page 26

1.1.2. Cht bn dn thun (intrinsic)

Hai cht bn dn thun in hnh l Ge v Si c nng lng vng cm:

Eg(Ge)=0,72eV v Eg(Si)=1,12eV, thuc nhm IV trong h thng tun hon.

Trong mng tinh th, cc nguyn t Ge (Si) lin kt vi nhau theo kiu cng ha

tr (cc nguyn t a ra cc electron ha tr lin kt vi cc nguyn t xung

quanh). Cht bn dn thun thc cht khng phi l mt cht cch in tt v

cng khng phi l mt cht dn in tt. Ti nhit phng, dn in ca Si

bng khong 10-10 dn in ca mt vt dn kim loi v bng khong 1014 ln

so vi mt cht cch in tt. Tuy nhin c th tng dn in ca cht bn

dn thun bng cch t nng hoc chiu sng tinh th bn dn tng s lng

ht dn. Khi c mt ngun nng lng bn ngoi kch thch, xy ra hin tng

ion ha cc nguyn t nt mng v sinh ra tng cp ht dn t do: in t v l

trng. iu ny tng ng vi s dch chuyn ca mt in t t 1 mc nng

lng trong vng ha tr ln 1 mc nng lng trong vng dn v ng thi

li 1 mc nng lng t do trong vng ha tr c gi l l trng. Cc ht dn

t do ny di tc dng ca in trng ngoi hoc do s chnh lch v nng

c kh nng dch chuyn c hng trong mng tinh th to nn dng in trong

cht bn dn. Mt c im quan trng trong cht bn dn l in t khng

phi l ht mang in duy nht m l trng cng c coi l ht mang in nn

dng in trong cht bn dn lun gm hai thnh phn do s chuyn di c

hng ca in t v l trng.

.

Trong cht bn dn thun, mt ca in t v l trng l bng nhau:

ni=pi

: in t : L trng

Hnh 2. C ch pht sinh cp ht dn t do trong cht bn dn thun


Page 27

Mt phng php hiu qu v n gin hn tng kh nng dn in ca

cht bn dn l pha tp cht.

1.1.3.Cht bn dn pha tp

a. Cht bn dn pha tp loi n

Tin hnh pha cc nguyn t thuc nhm 5 trong bng tun hon

(Antimony hoc Phosphorus) vo mng tinh th ca cht bn dn thun nh

cng ngh c bit vi nng cao (1010 n 1018 nguyn t/cm3). Nguyn t tp

cht lin kt vi cc nguyn t cht bn dn thun trong mng tinh th s tha

mt in t ha tr, lin kt yu vi ht nhn v d dng b ion ha nh 1 ngun

nng lng yu, tch khi ht nhn v tr thnh electron t do v to nn ion

dng tp cht bt ng.

Ti nhit phng, ton b cc nguyn t tp cht u b ion ha. Ngoi

ra, hin tng pht sinh ht dn ging nh c ch ca cht bn dn thun vn

xy ra nhng vi mc yu hn. Mc nng lng tp cht loi n hay loi cho

in t (donor) phn b bn trong vng cm, st y vng dn. Nu mt nguyn

t cht bn dn thun c thay th bi mt nguyn t tp cht th dn in

ca cht bn dn pha tp tng 105 ln so vi cht bn dn thun. Trong mng

tinh th tn ti nhiu ion dng tp cht bt ng v dng in trong cht bn

dn pha tp loi n gm 2 thnh phn : in t- ht dn a s (majority) c nng

l nn v l trng- ht dn thiu s (minority) c nng l pn ( nn pn ).

b. Cht bn dn pha tp loi p

Tin hnh pha tp cht thuc nhm 3 trong bng tun hon (Boron hoc

Aluminum) vo mng tinh th cht bn dn thun vi nng cao. Nguyn t

Mc nng lng tp cht loi n

Hnh 3. C ch pht sinh ht dn trong cht bn dn pha tp loi n


Page 28

tp cht khi lin kt vi cc nguyn t cht bn dn thun trong mng tinh th s

thiu mt in t ha tr nn 1 lin kt b khuyt v c gi l l trng d dng

nhn in t, v khi nguyn t tp cht b ion ha to nn ion m tp cht bt

ng ng thi pht sinh l trng t do . Mc nng lng tp cht loi p hay

loi nhn in t (acceptor) nm trong vng cm st nh vng ha tr.

Ngoi ra, vn xy ra c ch pht sinh ht dn ging trong cht bn dn

thun vi mc yu hn. Trong mng tinh th tn ti nhiu ion m tp cht bt

ng v dng in trong cht bn dn pha tp loi p gm 2 thnh phn: l trng-

ht dn a s c nng pp v in t-ht dn thiu s c nng np

( pp np ).

Kt lun:

trng thi cn bng, tch s nng 2 loi ht dn lun l hng s

kT

E

vciiippnn

g

eNNnpnpnpn

2

Trong cht bn dn pha tp loi n: nin pnn nn:

Dn Nn

Trong cht bn dn pha tp loi p: pip npp nn:

Ap Np

1.2. Diode bn dn

Khi cho 2 n tinh th bn dn tp cht loi p v n tip xc cng ngh vi

nhau hnh thnh nn chuyn tip p-n (junction p-n).

1.2.1. S hnh thnh min in tch khng gian:

Mc nng lng tp cht loi p

Hnh 4. C ch pht sinh ht dn trong cht bn dn pha tp loi p


Page 29

Do c s chnh lch v nng np pp v pn nn nn ti min tip

xc xy ra hin tng khuch tn cc ht dn a s (l trng chuyn ng t

pn v in t chuyn ng t np), gy nn dng khuch tn gm 2 thnh

phn: dng chuyn di c hng ca in t v ca l trng c chiu quy c

pn. Nu mc pha tp ca 2 ming bn dn loi p v loi n bng nhau th 2

thnh phn dng c cng bng nhau, nhng thng thng ngi ta pha tp 2

ming bn dn vi nng khc nhau (

DA NN ).

Khi cc ht dn a s dch chuyn li cc ion tp cht gn b mt tip

gip, do xut hin mt lp in tch khi do ion tp cht to nn, c rng

lo, ngho ht dn a s v c in tr rt ln, c gi l min ngho, hay tip

gip Jp-n hoc chuyn tip Jp-n, min ngho n su vo min bn dn c pha

tp vi nng thp hn ( onopDA llNN ), ng thi xut hin mt in

trng trong c hng t np, c gi l in trng tip xc Etx. Hnh thnh

nn mt hng ro in th hay mt in th tip xc otxtx lEU . in trng

Etx cn tr chuyn ng khuch tn v nhng gy nn chuyn ng tri ca cc

ht dn thiu s qua min tip xc, dng tri ngc chiu vi dng khuch tn.

Nu chuyn ng khuch tn xy ra mnh, rng min ngho tng, in trng

Etx tng, cn tr chuyn ng khuch tn v kch thch chuyn ng tri v dn

ti trng thi cn bng ng: Ikt=Itri, tc l vn tn ti 2 dng in nhng ngc

chiu nhau. Hiu in th tip xc c xc nh:

p

n

n

ptx

n

n

q

kT

p

p

q

kTU lnln (2)

p n

Ikt

Hnh 5. Cu trc ca chuyn tip p-n

p n

Etx

Jp_n


Page 30

Chuyn ng tri l s chuyn di c hng ca cc ht dn di tc ng

ca t trng cn chuyn ng khuch tn c gy nn bi s chnh lch v

nng . Vi nhng iu kin tiu chun v ti nhit phng, hiu in th tip

xc (Utx) c gi tr khong 0,3V vi tip gip lm t Ge v 0,6V vi tip gip

lm t Si.

1.2.2. Tip gip Jp-n khi c in trng ngoi

a. Phn cc thun

in trng ngoi Eng tp trung ch yu trong min in tch khng gian

c chiu ngc chiu vi Etx (cc dngp v cc mn). Theo nguyn l xp

chng, in trng tng ngtxt EEE

hay ngtxt EEE . Vy cng in

trng tng txt EE , rng min ngho gim, lm tng chuyn ng khuch

tn ca ht dn a s, hay cng dng in Ikt tng, cng dng in tri

Itri gim. Ngi ta gi l hin tng phun ht dn a s qua tip gip Jp-n v

trng hp ny c gi l phn cc thun cho chuyn tip p-n. (Thng in

p phn cc thun nh hn in p tip xc hay hng ro th).

b. Phn cc ngc

in trng ngoi Eng cng chiu vi Etx (cc dngn, cc mp).

Khi cng in trng tng ngtxt EEE

hay txngtxt EEEE

rng min ngho tng, cn tr chuyn ng khuch tn, dng khuch tn Ikt gim

ti 0, dng tri Itr tng cht t v nhanh chng t c gi tr bo ha c gi

l dng ngc bo ha. Trng hp ny c gi l phn cc ngc cho chuyn

tip p-n.

p

+ _ n

Hnh 6. Phn cc thun cho Jp-n

Etx

Eng

p _ +

n

Etx

Eng


Page 31

1.2.3. Cu to, k hiu v nguyn l lm vic ca diode bn dn

a.Cu to v k hiu

Diode bn dn c cu to l mt chuyn tip p-n vi mt in cc ni ti

min p gi l Anode(A) v mt in cc c ni ti min n c gi l

Cathode (K), lin kt c gi l lin kt Ohmic v c th coi l mt in tr

c gi tr nh ni tip vi diode mch ngoi.

b.Nguyn l hot ng v c tuyn Volt_Ampere

Di tc ng ca in trng ngoi diode hot ng nh van mt chiu:

Khi phn cc thun (UAK>0)

Ban u, khi in p UAK vn cn nh dng ID tng theo hm s m

ca in p:

1. T

AK

Um

U

SD eII (3)

Trong :

Is(T) l dng ngc bo ha, ph thuc vo nng ca ht dn thiu

s ti trng thi cn bng, ph thuc vo bn cht cu to ca cht bn dn pha

tp v do ph thuc vo nhit .

p

n

Hnh 8. Cu to v k hiu ca Diode

A K

Jp-n

Etx

A K


Page 32

UT: Th nhit (Thermal Voltage); UT= mVq

kT26 ; k=1,38.10

-23J/K:

hng s Boltzman; q=1,6.10-19 (C) in tch ca ht mang in; K: nhit c

o bng n v Kenvil.

m: h s hiu chnh gia l thuyt v thc t.

Nu UAK>0,1V c th biu din hm quan h gia ID v UAK:

T

AK

Um

U

SD eII.

. (4)

Tuy nhin vi gi tr UAK ln th quan h gia dng ID v in p UAK

khng theo phng trnh trn. Khi UAK t gi tr bng in p ngng Uth diode

dn mnh, dng ID tng mnh, tip gip p-n c coi l in tr thun c gi tr

rt nh.

Khi phn cc ngc (UAK


Page 33

Vy trong trng hp phn cc thun dng ID c gi tr ln do s phun

ht dn a s qua tip gip p-n, ngc li trong trng hp phn cc ngc

dng qua diode ch l dng ngc bo ha Is c gi tr rt nh. iu ny

th hin tnh cht van mt chiu ca diode.

Vng nh thng (UAK


Page 34

C ch nh thng thc l: Do cc ht thiu s c gia tc trong

in trng mnh va chm vi cc nguyn t nt mng, cung cp nng lng

cho cc electron ha tr c th bt ra khi ht nhn tr thnh electron t do, hin

tng ion ha nguyn t ny c gi l hin tng ion ha do va chm, lm

pht sinh cc cp in t - l trng t do. V cc ht dn mi c pht sinh tip

tc c gia tc trong in trng mnh v ion ha cc nguyn t khc khi s

ht dn trong min in tch khng gian tng ln t ngt nh thc l lm cho

in tr sut gim v cng dng ngc tng t bin, chuyn tip p-n b

nh thng. Trong hu ht cc chuyn tip p-n, nh thng theo c ch thc l

lun chim u th.

C ch nh thng xuyn hm: Cng in trng mnh cng

cung cp nng lng cho cc electron ha tr ca nguyn t cht bn dn thun

c th bt ra khi ht nhn tr thnh electron t do. Hin tng ion ha ny

c gi l ion ha do in trng. Nu cng in trng ngc ln lm

s lng cc ht dn tng ln mt cch ng k hay cng dng in ngc

tng t ngt v tip gip p-n b nh thng. C th hnh dung trong c ch nh

thng xuyn hm cc electron t do t vng ha tr ca min p dch chuyn

xuyn qua rng ng hm sang vng dn ca min n.

1.2.4. ng dng

a. Chnh lu: Bin i in p xoay chiu thnh in p mt chiu (nn

in)

Chnh lu na chu k (half-wave Rectifier) :

Diode c coi l l tng: UAK 0 : diode thng hon ton

=vs1kHz

-12/12V

D

R 1k


Page 35

UAK


Page 36

Chnh lu 2 na chu k(Full-wave Rectifier) :

Trong na chu k dng: diode D1 thng, D2 ngt, dng qua D1 v ti

RL

Trong na chu k m: diode D1 ngt v D2 thng, dng qua D2 v ti RL

Vy trn ti RL xut hin in p trong c 2 na chu k

Chnh lu cu(Bridge Rectifier) :

Hnh 11. Chnh lu hai na chu k

v1vi

D2 RL

D1

Hnh 12.Chnh lu cu

=

svDB

50 Hz

V1-12/12V

R 1k


Page 37

Chnh lu vi t lc C: Tn hiu sau chnh lu c h s gn ln, t C ng

vai tr l phng in p do hin tng phng np hay cn gi l lc gim h

s gn.

b. Hn bin (clipper)

Tn hiu xoay chiu u ra b gii hn ti mt gi tr in p xc nh.

Mch hn bin trn hoc mch hn bin di c mc theo kiu ni tip hay

kiu song song

Mch hn bin mc ni tip: Hn ch trn mc E (a)

Hn ch di mc E (b)

Mch hn bin mc song song: Hn ch trn mc E (a)

Hn ch di mc E (b)

=

=

vs

1kHz

-12/12V

+E 5V

D

R 10k =

=

vs

1kHz

-12/12V

+E 5V

D

R 10k

sv2kHz

-10/10V

+E

5V

D

R

22k

vsD

+E

5V2kHz

-12/12V

R

47k


Page 38


Page 39

c. Mch ghim (clamper)

Tn hiu ac u ra c dch (shift) mt gi tr in p dc so vi tn hiu

in p u vo khi phc thnh phn dc ca tn hiu u vo.

Ti thi im ban u, t cha tch in. Trong na chu k dng u tin

ca tn hiu u vo, khi in p u vo ln hn in p ngng ca diode,

diode thng hon ton, t c tch in n gi tr cc i: Ucmax=vi-E (trong

Vi l bin in p u vo). Do t khng th phng in qua diode nn, vo=vi-

Ucmax, hay c th ni in p u ra c dch so vi in p u vo mt gi tr

in p dc (Ucmax).

Hnh 14. Mch ghim in p

=

vs

C

1kHz

-10/10V

+E 2V

D


Page 40

1.2.5. Mt s diode c bit

a. Diode Zener (diode n p)

Diode Zener l mt diode c bit c pha tp cht vi nng rt cao

v c th hot ng trong min nh thng ca c tuyn Volt-Ampere. Trong

min phn cc thun, diode Zener hot ng nh mt diode chnh lu thng.

Trong min phn cc ngc, khi in p phn cc ngc t c gi tr in p

Uz=-UBR, dng qua diode (Iz) tng mnh, nhng in p Uz=const, nn diode

Zener c s dng n nh in p mt chiu.

b. Varactor diode (diode bin dung)

Tip gip p-n khi c phn cc ngc c th c coi tng ng nh

mt t in (do min in tch khng gian ngho ht dn a s nn c in tr

sut ln), rng ca min in tch khng gian ph thuc vo in p phn cc

ngc nn gi tr in dung ca min in tch khng gian thay i theo gi tr

in p phn cc ngc. Diode bin dung c ng dng trong cc mch cng

hng chn tn: Mch iu chnh tn s t ng - AFC (Automatic frequency

Controller) hay VCO (Voltage-Controlled Oscillator).


Page 41

c. Photo diode (Diode thu quang)

L mt linh kin bin i quang nng thnh in nng. C cu to ging

diode chnh lu nhng v bc cch in bn ngoi c mt phn l knh hoc

thy tinh trong sut nhn nh sng chiu vo tip gip p-n. Diode thu quang

cng hot ng trong min phn cc ngc. Khi nh sng chiu vo tip gip p-

n cung cp nng lng cho cc electron ha tr c th bt ra khi ht nhn

nguyn t, lm pht sinh cp ht dn in t-l trng t do. Cng dng

ngc tng tuyn tnh vi cng nh sng chiu vo tip gip. Diode thu

quang c s dng rng ri trong cc h thng iu khin t ng theo cng

nh sng.

d. LED (Light Emitting Diode- diode pht quang)

L linh kin bin i in nng thnh quang nng, c pha tp vi nng

cao tinh th bn dn tp cht loi p hoc loi n ti mc suy bin, rng

vng cm hp li. Khi mt in p thun c t vo chuyn tip p-n, cc ht

dn a s chuyn ng khuch tn qua tip gip p-n v tr thnh ht thiu s

tri, sau chng khuch tn su vo n tinh th bn dn trung ha v in v

ti hp vi ht dn a s v khi pht ra nh sng. Hin tng l khi cc

electron chuyn t mc nng lng cao xung mc nng lng thp km theo

pht x cc photon, c gi l hin tng ti hp ht dn. LED c th pht ra

nh sng trng thy ph thuc vo in p ngng. in p ngng ri trn

LED thng cao hn diode chnh lu.


Page 42

1.3. Transisor

Transistor l mt linh kin in t gm 3 in cc c kh nng khuch i dng,

in p hay cng sut. Nguyn l c bn ca Transistor l in p gia 2 cc

ca n iu khin cng dng in ca cc th 3. C 2 loi Transistor:

Transistor lng cc ( Bipolar Juction Transistor BJT) v Transistor trng

(Field-Effect Transistor FET). Mi Transistor c mt u im v c tuyn ring

v do cng c ng dng trong nhng phm vi ring.

3.3. Transisor lng cc (Bipolar Junction Transistor - BJT)

BJT gm 3 lp bn dn tp cht tip xc cng ngh xen k nhau, hnh

thnh nn 2 tip gip Jp-n (phi tuyn) kt hp vi 3 tip xc Ohmic (tuyn tnh)

v a ra 3 in cc: Emitter (Cc pht), Base (Cc gc) v Collector (Cc

gp). C 2 kt cu c trng: npn v pnp nhng Transistor loi npn c s

dng rng ri hn.

1.3.1. Cu to, k hiu v nguyn l hot ng ca Transistor

a. Cu to, k hiu

Transistor

BJT

MOSFET

FET

JFET

Knh n Knh t sn Knh cm ng

npn pnp

Knh n Knh p Knh n Knh p

Knh p

Hnh 15. S phn loi Transistor


Page 43

Ba min ca Transistor c pha tp vi nng khc nhau v c rng

cng khc nhau:

+ Min Emitter pha tp vi nng cao nht v rng trung bnh

+ Min Base pha tp vi nng nh nht v mng nht

+ Min Collector pha tp vi nng trung bnh nhng rng ln nht

Tip gip Emitter - Base c gi l: JB-E (JE)

Tip gip Collector - Base c gi l: JB-C (JC)

C th coi Transistor tng ng vi 2 diode mc i nhau nhng khng

c ngha c mc 2 diode i nhau c th hot ng ging nh Transistor v khi

khng c s tng h ln nhau gia 2 tip gip JB-E v JB-C.

Transistor c 2 tip gip p-n nn c th c 4 kh nng phn cc cho 2 tip

gip

JE JC Min lm vic ng dng

Phn cc ngc Phn cc ngc Min ct Kha

Phn cc thun Phn cc ngc Min tch cc Khuch

Hnh 16. Cu to v k hiu ca BJT


Page 44

i

Phn cc thun Phn cc thun Min bo ha Kha

Phn cc ngc Phn cc thun Tch cc

ngc

Transistor hot ng trong ch khuch i (hay trong min tch

cc), JE c phn cc thun v JC phn cc ngc.

Nu JE v JC u c phn cc thun hoc u c phn cc ngc th

Transistor hot ng nh mt kha in t vi hai trng thi: Trng thi ngt v

trng thi thng bo ha, c ng dng trong cc mch xung v mch s.

b. Nguyn l hot ng ( npn)

Khi JE c phn cc thun (UBE>0), dng in qua JE ch yu l dng

khuch tn ca cc ht dn a s, in t t min Emitter c phun vo min

Base ng thi l trng t min Base khuch tn sang min Emitter, tuy nhin

do nng pha tp ca min Base rt thp nn cng dng l trng nh hn

rt nhiu so vi cng dng in t, nn c th coi dng IE l dng ca cc

in t, ph thuc ch yu vo in p UBE.

Khi cc in t c phun t min Emitter sang min Base, tip tc

khuch tn su vo trong min Base v xy ra hin tng ti hp ht dn, dng

IB gm 2 thnh phn: dng l trng (ht dn a s) khuch tn sang min Emitter

(IB1) v dng l trng ti hp vi electron (IB2).

Do rng ca min Base rt mng nn ch c mt s rt t cc in t ti

hp vi l trng trong min Base cn a s in t ti c chuyn tip JC, JC

phn cc ngc nn electron c cun sang min Collector. Dng in IC trong

min Collector gm 2 thnh phn: ICBo: dng ngc bo ha (dng tri ca ht

dn thiu s) v dng cun ca cc ht thiu s tri t min Base sang min

Collector. Dng ngc bo ha ICBo c gi tr rt nh nn dng cun ca cc ht

dn thiu s tri l thnh phn ch yu ca dng IC, hay EC II nn ch ph

thuc vo in p UBE m c lp vi in p UCB, tc l dng IC c iu

khin bi in p UBE, l nguyn l hot ng c bn ca Transistor.


Page 45

0CBEC III (5)

BCE III (6)

Vy: 0CBCBC IIII hay CBoBC III

1

1

1

t

1 ta c:

CEoBCBoBC IIIII ..1. (7)

Trong : l h s truyn t dng in 1 , cng gn 1 Transistor

cng tt.

: l h s khuch i dng tnh (50-300)

Vy: = /(1+ )

1.3.2. Cc cch mc ca BJT

Nu coi Transistor nh mng 4 cc, khi phi c mt cc chung cho c

u vo v u ra. C th c 3 cch mc (kt cu): CE (Common Emitter);

CB(Common Base) v CC (Common Collector).

a. Kt cu CE:

c tuyn vo: constCEBEB UUfI

Do JE phn cc thun m EB II nn c tuyn vo trong trng hp

ny ging c tuyn ca chuyn tip p-n phn cc thun. Nu UCE tng, m

a) b) c

Hnh 17. Cc kt cu ca BJT a. CE b. CB c.CC

IB

IC

IE

IE

IB

IC

IB

IE

IC


Page 46

UBE=const khi UCB tng, hay in p phn cc ngc tng, s ht n c

tip gip Jc cng nhiu hay s ht b ti kt hp trong min Base cng t, nn

dng IB gim.

c tuyn ra: constBCEC IUfI

Min khuch i (gn gc), dc ca c tuyn kh ln. Khi UCE tng,

in p UCB cng tng, phn cc ngc ca chuyn tip Jc tng nn IC tng

tuyn tnh theo in p UCE. Khi UCE t gi tr ln ( V2 ) dng Ic t gi tr

bo ha, BC II . tc l khng ph thuc vo UCE nhng UCE qu ln th IC

tng t ngt do xy ra hin tng nh thng do hiu ng thc l hay hiu ng

xuyn hm. Nu UCE


Page 47

b. Kt cu CB:

c tuyn vo: constCBBEE UUfI

Do JE phn cc thun nn c tuyn vo c dng ging vi c tuyn ca

diode khi phn cc thun. Khi UBE=const, UCB tng, phn cc ngc tng, vng

ngho Jc rng ra, khong cch hiu dng gia 2 min JE v Jc gim nn dng IE

tng.

c tuyn ra: constECBC IUfI

Do constIE , EC II nn khi thay i UCB th dng CI thay i

khng ng k. Mt im khc bit l khi UCB gim ti 0 nhng dng Ic cha

gim ti 0. l do khi UCB=0, bn thn chuyn tip Jc vn cn in th tip

xc, chnh in th tip xc ny cun cc ht dn t Base sang min Collector

nn dng CI vn c gi tr khc 0. dng 0CI , chuyn tip Jc phi c

phn cc thun, khi Transistor chuyn sang hot ng trong ch bo ha.

iu ng ch l khi IE=0 nhng vn c thnh phn dng r ICE0 nn 0CI .

c. Kt cu CC:

c tuyn vo: constUUfI CECBB

Do khi Transistor hot ng trong ch khuch i, in p UBE lun

gi khng i (UBE=0,7V i vi Si v 0,3V i vi Ge). Nn UCB=UCE-

UBE=const, UCB khng ph thuc vo IB.

c tuyn ra: constBCEE IUfI Do EC II nn c tuyn ra trong

trng hp ny c dng ging vi c tuyn ra trong trng hp CE.

UCB(V)

UCE1 UCE2>UCE1

IB(A)

0

IE(mA)

UCE(V)

IB=150A

125A

100A

IB=0

Hnh 19. c tuyn vo v c tuyn ra ca kt cu CC


Page 48

1.3.3. Phn cc BJT:

Phn cc l cp in p mt chiu cho cc in cc ca Transistor.

BJT hot ng trong ch khuch i JE lun phn cc thun v Jc lun phn

cc ngc.

ng ti tnh: )( OO UfI l mi quan h gia cng dng in v

in p u ra khi Transistor c mc trong mt mch c th (khi c ti).

im cng tc tnh l im nm trn ng ti tnh xc nh cng

dng in v in p u ra khi khng c tn hiu xoay chiu t vo. im cng

tc tnh chnh l giao im ca ng ti tnh v c tuyn ra ng vi gi tr

IB=const. ng ti tnh c v trn cng h trc ta vi c tuyn ra.

n nh im cng tc tnh khi nhit thay i

Transistor l mt linh kin rt nhy cm vi nhit . Hai thng s ca

Transistor nhy cm vi nhit nht l in p UBE v cng dng

ngc bo ha ICBo. Nu dng ICBo tng, lm cho dng IC tng, s lng ht dn

qua chuyn tip Jc tng lm cho s va chm gia cc ht dn vi mng tinh th

tng, khi lm cho nhit tng v tip tc lm ICBo tng, c th nhit ca

IC(mA)

UCE(V)

IB0

IB1

IBQ Q

ICmax

VCC

ng ti tnh

Hnh 20. ng ti tnh v im lm vic tnh


Page 49

Transistor tng mi. Hin tng ny c gi l hiu ng qu nhit. Hiu ng

qu nhit lm thay i im cng tc tnh v nu khng c bin php hn ch s

lm hng Transistor. Khi nhit thay i in p UBE cng thay i v do

cng lm im cng tc tnh thay i. Tuy nhin, trong iu kin bnh thng

nh hng ca dng ngc bo ha ICBo n IC nhiu hn nh hng ca in p

UBE nn khi ni n nh hng ca nhit n im cng tc tnh thng ni

n nh hng ca dng bo ha ICBo, v a ra khi nim h s n nh nhit:

CBo

C

I

IS

CBoBC III 1.

Nn:

C

BCBo

C

I

II

IS

1

1 (8)

H s S cng nh, tnh n nh i vi nhit cng cao.

Cc phng php phn cc cho Transistor n nh im cng tc tnh

1.4. Cc ph-ng php phn cc cho BJT

1.4.1 Phn cc cho BJT Phn cc cho BJT l xc nh im lm vic ban u (im lm vic tnh Q - Quiescent) bng cc ngun mt chiu.

Trn c tuyn vo, im Q c to : uBE= UBEQ; iB = IBQ Trn c tuyn ra, im Q c to : uCE= UCEQ; iC = ICQ Nh- vy phn cc cho BJT phi to ra hai ngun mt chiu: UBB, RB

ca vo v UCC, RC ca ra (hnh 3-5). *Ca vo

Ph-ng trnh Kirchhoff cho vng mch ca vo: BEBBBB uRiU (3.12)

-ng ti ca vo:

B

BEBBB

R

uUi

(3.13)


Page 50

RB

RC

a B

b'

EUBB

UCC

C

b

iB

+-

uBE

iC

+

uCE

-

iE

Hnh 3-5 Phn cc cho BJT

im lm vic ca vo l to giao im Q gia -ng ti (3.13) vi c tuyn V-A ca vo ca BJT (3.9). To Q ca vo trn hnh 3-6a s l: VUUQu fBEQBE 6,0)( (3.14)

B

BBBQB

R

VUIQi

6,0)(

(3.15)

*Ca ra

Ph-ng trnh Kirchhoff cho vng mch ca ra:

CECCCC uRiU (3.16)

-ng ti ca ra:

C

CECCC

R

uUi

(3.17)

Hnh 3-6 im lm vic Q

To Q ca ra trn hnh 3-6b s l: Dng in ICQ t-ng ng IBQ ca vo khi b qua dng in ng-c ICB0:

BQFCQC IIQi )( (3.18)

in p UCEQ theo (3.16) s l:

CCQCCCEQCE RIUUQu )( (3.19)

1.4.2 Cc ph-ng php phn cc c bn cho BJT I. Phn cc bng dng in baz

iB

uBE

iC

uCE UBEQ Uf

a) c tuyn vo b) c tuyn ra

)1/

(0

TU

BEu

eB

IB

i

B

BEBBB

R

uUi

Q IBQ

Q IQB

UCE0 UCEQ

ICQ

C

CECCC

R

uUi

C

CC

R

U

UCC

B

BB

R

U

UBB


Page 51

R1R2

a B

b

b'

C

E

iB

iC

(a)

+ UCC -

+uBE

-

+

uCE-

R1

R2

R3

a B

b

b'

C

E

iB

iC

(b)

+ UCC -

+uBE

-

+uCE

-

Hnh 3-7 Cc ph-ng php phn cc c bn cho BJT

Phn cc bng dng in baz -c thc hin theo s hnh 3-7a vi

mt ngun mt chiu UCC duy nht. Ngun UBB, RB -c to ra t ngun UCC, R1. Ngun UCC, RC -c to ra t ngun UCC, R2.

Mch phn cc hnh 3-7a c th -c thay th t-ng -ng bng s hnh 3-5 vi cc tham s t-ng -ng:

UBB= UCC (3.20)

RB= R1; RC= R2 (3.21)

Cc gi tr phn cc -c xc nh theo s hnh 3-5 theo cc cng thc: (3.14), (3.15), (3.18), (3.19).

C th xc nh cc gi tr phn cc trc tip t s hnh 3-7a, -c cc kt qu nh- trn, ch thay th cc gi tr t-ng ng theo cc cng thc (3.20) v (3.21). II. Phn cc bng phn p

Mch phn cc bng mch phn p -c thc hin theo s hnh 3-17b t mt ngun mt chiu UCC v cc in tr R1, R2, R3. S ny c th quy i t-ng -ng v s hnh 3-5. Mch phn p ca vo: UCC v cc in tr R1, R2, c th -c thay th bng ngun p UBB, RB. Cc gi tr t-ng -ng nh- sau:

CCBB URR

RU

21

2

(3.22)

21

21

RR

RRRB

(3.23)

Mch ca ra: UCC, R3 t-ng -ng vi ngun p: UCC, RC: UCC= UCC (3.24)

RC= R3 (3.25)


Page 52

Cc gi tr phn cc -c xc nh t s hnh 3-5 theo cc cng thc: (3.14), (3.15), (3.18), (3.19). 3.4.3 n nh ch lm vic cho BJT Trong qu trnh lm vic, im lm vic ca BJT c th b tri khi v tr chn ngay c khi ch-a c tc ng ca cc tn hiu c ch do mt s hiu ng mt n nh tc ng nh-: nhit thay i, ngun phn cc mt chiu thay i v khi tham s ca cc phn t trong mch thay i. BJT lm vic bnh th-ng, khng nh h-ng n ch tiu cht l-ng ca mch, trong cc s mch in t s dng BJT th-ng thc hin cc bin php n nh:

- -a thm vo mch cc phn t hoc cc on mch n nh nhit , n nh ngun mt chiu.

- Thay th cc phn t mch c tham s n nh hn. - To ra bin i ng-c b tr cho nhng bin i gy mt n nh hoc

ph-ng php cung cp ng-c - ph-ng php hi tip m, ph-ng php ny s -c nghin cu trong ch-ng khuch i.

i vi BJT, in p phn cc thun tip gip mit (uBE) v dng in ng-c tip gip Clct (ICB0) u ph thuc vo nhit . Dng in ICB0 ph thuc ch yu vo nhit .

R1

R2

R3

B

C

E

ICB0

(b)

+ UCC -

+uBE

-

+uCE

-ID0

R1

R2

R3

B

C

E

(a)

+ UCC -

+uBE

-

+uCE

-

D

RTt0

Hnh 3-8 n nh bng in tr nhit (a) v it phn cc ng-c (b)

Theo cch th nht, c th mc song song vi tip gip mit in tr

nhit c h s nhit m (hnh 3-8a). Khi nhit tng, dng Clct tng ng thi in tr nhit gim lm gim uBE, dng Baz gim ko theo dng Clct cng gim theo b tr mc tng dng ny do nhit .

Hnh 3-8b l s b tr mt n nh nhit gy bi ICB0 bng dng in ng-c ca it ID0 (dng ng-c bo ho Is). Tt c cc bin i ca ICB0 theo nhit u -c b tr bng cc bin i ca ID0 m t nh h-ng n cc dng in khc ca BJT.


Page 53

Ph-ng php hi tip m -c s dng nhiu n nh ch lm vic cho BJT. Hnh 3-9 l cc ph-ng n thng dng trong cc mch in t.

R2

a B

b

b'

C

E

iB

iB+iC

(a)

+ UCC -

+uBE

-

+

uCE-

R1

R2

R3

a B

b

b'

C

E

iB

iC

(b)

+ UCC -

+uBE

-

+uCE

-

R1

R4

iEiE

Hnh 3-9 n nh ch lm vic ca BJT bng hi tip m.

S hnh 3-9a l n nh bng in p song song. Nguyn l nh- sau:

khi nhit tng, dng iC tng, in p trn R2 tng, ubb gim, in p thnh phn phn p uaa= uBE gim theo dn n iB gim lm cho iC gim, ko iC v gi tr n nh.

Cc gi tr phn cc c th xc nh trc tip t s : UCC=UR2+UR1+uBE

=(iC+iB)R2+iBR1+uBE

= iB(F+1)R2+ iBR1+uBE

21 )1( RR

uUi

F

BECCB

To im Q u vo c in p BE nh- 3.14: VUBEQ 6,0 ,v:

21 )1(

6,0

RR

VUI

F

CCBQ

(3.26)

To im Q u ra c dng clct nh- 3.18: BQFCQ II , v:

2)( RIIUU CQBQCCCEQ (3.27)

Ph-ng php phn cc c hi tip trn clct nn cn -c gi l phn

cc hi tip (phn hi) clct.

S hnh 3-9b l n nh bng hi tip dng in ni tip. Nguyn l nh-

sau: khi nhit tng, dng iC tng, dng iE = (iC+ iB) tng lm UR4 tng, in p uBE= (UR2- UR4) gim, dn n iB gim lm cho iC gim, ko iC v gi tr n nh.

Cc gi tr phn cc c th xc nh bng cch quy v s t-ng -ng hnh 3-10. Cc gi tr t-ng -ng theo cc cng thc t 3.22 n 2.25 v RE=R4.


Page 54

RB

RC

a B

b'

EUBB

UCC

C

b

iB +-

uBE

iC+

uCE-

iE

RE

Hnh 3-10 S t-ng -ng mch hnh 3-9b

RiuRiU EBEBBBB ; BFE ii )1(

EFB

BEBBB

RR

uUi

)1(

To im Q u vo c in p BE nh- 3.14: VUBEQ 6,0 ,v:

EFB

BBBQ

RR

VUI

)1(

6,0

(3.28)

To im Q u ra c dng clct nh- 3.18: BQFCQ II , v:

CCQECQBQCCCEQ RIRIIUU )( (3.29)

Ph-ng php phn cc c hi tip trn mit nn cn -c gi l phn cc

hi tip (phn hi) mit.

1.4.4 Cc ch lm vic ca BJT

I. c tnh ti

Xt cc c tuyn tnh trong iu kin gi mt tham s no c nh: c tuyn vo khi mc E chung l quan h gia dng iB v uBE ng vi cc hng s uCE, c tuyn ra l quan h gia dng iC v uCE ng vi cc hng s iB. Khi BJT lm vic vi ch c ti, quan h dng v p theo quy lut -ng ti, cc dng in v in p trn cc cc u thay i nn gi l ch ng.

Phn tch c tnh ti ca ra ca BJT trong mch in hnh 3-11a. * Ti mt chiu

Khi lm vic vi ngun mt chiu, t in coi nh- h mch, BJT ch c mt ti duy nht l RC, -ng ti theo biu thc 3.17 tnh ring cho thnh phn mt chiu vi iC= IC v uCE= UCE s l:

C

CECCC

R

UUI

(3.30)

Trong IC l dng mt chiu qua RC v UCE l in p mt chiu trn CE. dc ca -ng ti mt chiu ph thuc vo RC:


Page 55

)1

(CR

acrtg (3.31)

R1

R2

RC

iB

iC

(a)

+ UCC -

+uBE

-

+uCE

- Rt

C

Q

M

N

Ti xoay chiu

Ti mt chiu

iC

uCEUCE0

PCmax

UCbh UCEQ

ICQ

CR

CCU

UCC

IBmax

iB=0

ICbh

III

II

I

(b)

iE

ICmax

Parabn bo ho

IC

Hnh 3-11 Mch BJT c ti (a) v c tnh ti ca BJT (b) -ng ti mt chiu c dc (-1/RC) ph thuc ti mt chiu: RC

* Ti xoay chiu

Khi lm vic vi tn hiu xoay chiu, t in C coi nh- ngn mch. Theo nguyn l xp chng, UCC i vi tn hiu xoay chiu cng coi nh- ngn mch. Ti xoay chiu bao gm RC mc song song vi Rt:

tC

tCtxc

RR

RRR

(3.32)

-ng ti xoay chiu c dc (-1/Rtxc) ph thuc gi tr ti xoay chiu Rtxc:

)1

('txcR

acrtg (3.33)

II. Cc ch lm vic ca BJT

Khi lm vic trong mch c ti, im lm vic ca BJT tr-t trn -ng ti. im lm vic c th ri vo cc ch sau y

Ch ct dng iB = 0, im lm vic trong vng I nm trn v pha d-i

-ng c tuyn tnh iB = 0. ch ny cc tip gip ca BJT hoc u khng -c phn cc hoc phn cc ng-c.

Dng in iB= 0

Dng in iC c gi tr *

0CBI 0 (hoc bng 0 khi khng phn cc)

in p uCE UCC Trn -ng ti mt chiu, im bin gii ct dng l M. Ch ny c dng in gn bng 0 v in p gn bng ngun t-ng

-ng vi trng thi ngt ca mt cng tc in.


Page 56

Ch tch cc, im lm vic trong vng II. Vng ny -c gii hn bi

c tuyn tnh iB = 0, -ng parabn bo ho, UCE0, PCmax, ICmax. ch tch cc, BJT c kh nng khuch i tuyn tnh nn cn -c gi

l ch khuch i tuyn tnh. Vng ny c dng in t ph thuc vo uCE, c

tuyn gn nh- song song vi trc honh cn gi l vng dng khng i. Lm vic ch tch cc, BJT c tip gip EB (JE) phn cc thun, tip gip BC (JC) phn cc ng-c.

Trn -ng ti mt chiu, ch tch cc l on MN. Ch tch cc th-ng -c s dng trong cc mch t-ng t. Ch bo ho, vng III nm trn v pha trn -ng parabn bo ho.

ch ny cc tip gip ca BJT u -c phn cc thun. Dng in baz: iB = IBmax Dng in iC =F.IBmax= hng s

in p uCE= UCbh 0 Trn -ng ti mt chiu, im bin gii bo ho l N. ch bo ho, dng iC lun l hng s v t gi tr cc i khi tng iB>

IBmax, khng iu khin -c dng in. Ch ny c dng in l cc i v in p gn bng 0 t-ng -ng vi trng thi ng ca mt cng tc in.

BJT lm vic hai ch ct dng v bo ho t-ng -ng vi hai trng thi ngt v ng ca mt cng tc in gi l ch kho. Ch kho ca BJT

l ch chuyn t ct dng sang bo ho v ng-c li. Ch ny -c s dng trong cc mch xung, s.


Page 57

CHNG 4: TRANSISTOR HIU NG TRNG (FET)

Ch-ng ny s nu cu to, phn tch cc hin t-ng vt l v cc quan h dng in, in p xy ra trong FET (Field Effect Transistor). Cu trc FET c knh bn dn loi P hoc loi N. Dng in chy qua knh dn -c iu khin bng in tr-ng thng qua thay i dn in ca knh. Vic phn tch s tp trung vo FET knh dn loi N, cn knh dn loi P c th phn tch t-ng t ch i ln v tr P cho N v i ln vai tr l trng cho in t.

4-1. Tranzito hiu ng tr-ng MOSFET knh dn N

4.1.1 MOSFET giu (Enhancement) knh dn N I. Cu to:

(a) K hiu:

(b) Hnh 4-1 Cu to (a) v k hiu (b) MOSFET giu knh dn N

MOSFET l tranzito hiu ng tr-ng FET (Field Effect Transistor) c cc

ca cch in IG (Insulated Gate) theo cng ngh MOS (Metal Oxide Semiconductor), cn c tn gi khc l IGFET.

Tranzito -c cu to t mt phin pha tp nh cht bn dn loi P. Bng cng ngh quang khc v khuch tn -a vo hai khi bn dn loi N pha tp cao, gn vi cc in cc ngun (S-Source) v cc mng (D-Drain), cch

nhau mt on trong phin gi l knh dn. Vng knh -c ph mt lp in

mi xt (SiO2). Lp kim loi (M-Metal) hoc bn dn a tinh th ph trn lp

Vng knh

L

Si02

Phin P

N+

N+

S D

B

G

D

S

B

G


Page 58

in mi gn vi cc ca (G-Gate). Lp in mi (O-Oxide) m bo cch in

mt chiu t phin bn dn (S-Semiconductor) n cc ca. Thc t dng qua lp in mi ch khong 10-15A hoc nh hn.

Cc kch th-c vt l quan trng ca MOSFET l rng cc ca W, di cc ca L, dy lp xt tox.

in cc gn vi phin l cc thn (B-Body), trong cc tranzito ri rc,

cc ny th-ng -c ni vi cc ngun, MOSFET cn li ba cc: S, G, D. Thng th-ng cu trc MOSFET l i xng nn c th i ln S v D m khng lm thay i tnh cht ca FET. II. MOSFET khi khng c in p cc ca uGS

Khi uDS > 0, tip gip PN gia D v phin phn cc ng-c, khng cho dng in chy qua lp ngho gia D v phin nn dng cc mng iD=0.

Khi uDS < 0 th tip gip gia phin v S cng phn cc ng-c, iD=0. Nh- vy, khi khng c uGS, MOSFET ch ct dng.

III. MOSFET khi c in p cc ca uGS

Hnh 4-2 MOSFET khi c in p cc ca uGS Gi thit uDS>0 v uGS >0. Do c uGS, hnh thnh in tr-ng trong lp xt.

D-i tc ng ca in tr-ng ny m cc l trng b y li su vo phin , li cc ion m Axpto khng dn in, MOSFET vn ch ct dng. Khi

tng uGS n gi tr ng-ng UTR, tr-ng lp xt bt u ht cc in t v pha cc ca hnh thnh lp o in t ni gia cc S v cc D gi l knh dn. Knh

dn bc cu qua vng ngho gia D v phin v vy c th cho dng iD chy qua. dn in ca knh dn tng theo uGS v khi uGS tng, mt cc in t trong knh dn tng, knh dn giu cc in t. Knh dn gm ton cc in t

nn gi l knh dn loi N. Do tn ti knh dn nn xut hin lp ngho mng

gia knh dn v phin hnh thnh lp ngn cch gia knh dn v phin . Knh dn -c hnh thnh do cm ng in tr-ng nn loi MOSFET ny cn -c gi l loi knh cm ng.

Phin P

N+

N+

B

- +

- +

uDS uGS

Lp ngho

Lp o in t


Page 59

Mi MOSFET c gi tr ng-ng xc nh, ph thuc vo mc pha tp trong phin v cc thng s ch to khc. i vi MOSFET giu gi tr ny khong 0,5 n 3 V.

1.MOSFET khi uDS nh:

Khi uDS cn nh (khong 1V) v uGS ln hn UTR (c knh dn), mt cc in t trong knh dn l ng u, MOSFET hot ng nhin tr c dng mng t l tuyn tnh vi uDS vi h s t l ph thuc vo uGS. Quan h ny -c biu din qua -ng lin nt trn th hnh 4-2. Vng lm vic ny -c gi l vng in tr.

c tuyn biu din vng in tr theo biu thc sau: iD= 2K(uGS- UTR)uDS (4.1)

in tr knh dn s l: uDS/iD v l hm bin i tuyn tnh theo uGS. Hng s K l h s dn ph thuc vo vt liu v kch th-c ch to:

Lt

WK

ox

oxe

2

(mA/ V2), (4.2)

trong el linh ng in t trong cht bn dn v oxl hng s in mi ca lp xt. W v L l kch th-c cc ca (L l chiu di dc theo knh dn v W l chiu rng cc ca), tox l dy lp xt. iD uDS

Hnh 4-2 c tuyn V-A khi uDS nh

Hnh 4-3 MOSFET khi tng uDS

Phin P

N+

N+

B

- +

- +

uDS uGS

Lp ngho

Knh dn


Page 60

Khi uDS tng, in p uDS phn b dc theo knh dn: ti cc ngun S bng

0 v ti cc D bng uDS. Chnh lch in p qua lp xt gn D l uGS-uDS nh hn uGS. in tr-ng trong lp xt gn cc mng s yu nn b dy knh dn s nh hn (hnh 4-3).

Do tit din knh dn gim dn v pha D nn c tuyn V-A tr nn phi tuyn (-ng t nt trn th hnh 4-2), ging ch in tch khng gian ca n in t nn gi l ch Trit (vng trit) :

iD= K[2(uGS- UTR)uDS-u2

DS] (4.3) 2.MOSFET khi uDS ln

Tip tc tng uDS ti gi tr gii hn m knh dn c dy bng khng (tht li) ti cc mng, in p st trn lp xt dn ti UTR.

Gi tr gii hn ca uDS -c tnh t iu kin: uGS- uDS = UTR => uDS= uGS- UTR (4.4)

Khi uDS tng n gi tr gii hn trn gi l ng-ng tht, dng iD vn tn ti do lp o in t vn ni ti cc mng -c nh in tr-ng phn cc ng-c ca lp ngho. Bin dng qua knh dn -c xc nh duy nht qua in p st trn knh dn. Dng in ny c gi tr khng i khi uDSv-t qu gi tr ng-ng tht (uGS- UTR). Vng lm vic ny gi l vng dng khng i:

iD= K(uGS- UTR)2 (4.5)

Nh- vy c tuyn V-A biu th quan h gia dng iD v in p uDS ca MOSFET giu knh dn N nh- trn hnh 4-4.

iD uDS= uGS- UTR uGS> UTR> 0 uGS= UTR uDS

Hnh 4-4 c tuyn V-A cc mng ca MOSFET giu knh dn N c tuyn gm ba vng:

Vng ct dng khi uGS< UTR (ch-a c knh dn): iD=0


Page 61

Vng Trit khi uGS> UTR(c knh dn) v 0 UTR v uDS (uGS- UTR): iD= K(uGS- UTR)

2 -ng bin gii gia vng trit v vng dng khng i l -ng

Parabn: iD= Ku2

DS , uDS= uGS- UTR. Trong vng trit iD ph thuc c vo uGS v uDS, vng dng khng i dng in ch ph thuc vo (uGS- UTR)

c tuyn V-A gia dng iG v uGS trn hnh 4-5a. Dng in cc ca qua lp in mi SiO2 lun bng khng vi mi gi tr ca uGS. c tuyn truyn dn gia iD v uGS trn hnh 4-5b. Dng in iD ch xut hin khi uGS> UTR. iG uGS (a) iD

Ch giu

| (b) UTR uGS

Hnh 4-5 c tuyn V-A cc ca (a) v c tuyn truyn dn (b)

ca MOSFET giu knh dn N 4.1.2. MOSFET ngho (Depletion) knh dn N (a)

uDS= uGS- UTR vng giu uGS>0

uGS=0 vng ngho uGS


Page 62

Hnh 4-6 K hiu (a) v c tnh V-A cc mng (b) ca MOSFET ngho knh dn N MOSFET knh dn N c th lm vic ch ngho khi uGS m gi l

MOSFET ngho knh dn N. Bng cch -a vo mt lp cc ion d-ng no t gia lp in mi v phin P, lp ion ny thu ht cc in t trong phin hnh thnh knh dn. Knh dn cn c th l khi bn dn N -a vo gia lp in mi v phin P. MOSFET ngho tn ti knh dn ngay c khi ch-a c uGS nn cn -c gi l MOSFET c knh t sn.

MOSFET ngho knh dn N -c k hiu nh- hnh 4-6a. MOSFET ngho knh dn N c in p ng-ng UTR m. c tuyn V-A gia dng mng v in p mng - ngun trn hnh 4-6b. c tuyn cng gm ba vng:

Vng ct dng khi uGS< UTR (uGS m hn UTR) iD=0

Vng Trit khi uGS> UTR (uGS d-ng hn UTR) v 0 UTR v uDS (uGS- UTR): iD= K(uGS- UTR)

2 Khi uGS > 0 v d-ng ln, l-ng cc in t trong knh dn tng, dng iD

tng, MOSFET lm vic ch giu. Khi uGS < 0 v m i, l-ng cc in t knh dn gim, iD gim, MOSFET lm vic ch ngho. Nh- vy MOSFET ngho c th lm vic c ch giu v ngho. Trn c tuyn truyn dn gia dng iD v uDS, dng iD xut hin t UTR c gi tr m (hnh 4-7). iD Ch ngho Ch giu

UTR uGS

Hnh 4-7 c tuyn truyn dn MOSFET ngho knh dn N c tuyn iG v uGS cng ging nh- MOSFET giu: dng iGlun bng

khng vi mi gi tr uGS. 4-2.Tranzito hiu ng tr-ng loi JFET knh dn n

4.2.1 Cu to JFET (Junction FET) l tranzito hiu ng tr-ng c tip gip PN. Cu to

v k hiu ca JFET knh dn N trn hnh 4-8.


Page 63

T phin pha tp nh loi P, bng cng ngh quang khc v khuch tn, ln l-t -a vo cc khi bn dn N lm knh dn v 3 khi bn dn N, P, N pha tp mnh gn vo cc cc S,G,D.

Tip gip PN gia knh dn v cc ca hnh thnh lp ngho. B rng lp ngho c th thay i -c nh in tr-ng phn cc ng-c gia knh dn v cc ca, do vy c th thay i -c tit din A ca knh dn.

in tr ca knh dn -c xc nh t in tr xut ca cht bn dn

loi N, chiu di hiu dng knh L, tit din hiu dng A. Dng in iD c th iu khin -c bng cch thay i in tr knh dn. S G D

(a) K hiu: D

G S (b)

Hnh 4-8 Cu to (a) v k hiu (b) ca JFET knh dn N

4.2.2 Hot ng ca JFET khi thay i uDS I. Khi uDS nh

uDS

S G D

Hnh 4-9 JFET khi uDS cn nh

N+

N+

P+

Knh dn N

Phin P

Lp ngho A

L

N+

N+

P+

A Knh dn N

Phin P

Lp ngho

- +

- +

uGS


Page 64

in p uGS m to ra phn cc ng-c gia cc ca v phin lm cho

rng lp ngho tng, tit din knh dn A nh li. Khi uGS m t n gi tr ng-ng UTR, lp ngho m rng hon ton knh dn, in tr knh dn tin ti v cng, iD= 0, JFET ri vo ch ct dng.

Khi uGS > UTR(uGS d-ng hn UTR), uDS cn nh, rng lp ngho ng u t S n D, quan h dng iD v uDS l tuyn tnh, JFET lm vic ch in

tr. Khi uDS tng, in p phn b dc theo knh dn tng dn t S n D, phn

cc ng-c tng, rng lp ngho m rng, knh dn c tit din nh dn, quan h dng iD v uDS tr nn phi tuyn, JFET lm vic ch trit.

uDS

S G D

Hnh 4-10 JFET khi uDS tng II. Khi uDS ln.

Khi uDS tng n khi tit din knh dn ti D tin ti 0, knh dn b tht li, cc in t tri qua vng tht vi tc khng i, dng iD qua knh dn s khng i, JFET lm vic ch dng khng i.

4.2.3. c tuyn V-A ca JFET

c tuyn V-A ca JFET biu din quan h gia iD v uDS (hnh 4-11) gm 3 vng nh- MOSFET: iD uGS >0 uGS=0V uGS


Page 65

Hnh 4-11 c tuyn V-A cc mng ca JFET Vng ct dng khi uGS< UTR (uGS m hn UTR):

iD=0 Vng trit khi uGS >UTR (uGS d-ng hn UTR) v 0UTR v uDS (uGS- UTR):

iD= K(uGS- UTR)2

H s K i vi JFET -c tnh theo cng thc sau:

2

P

DSS

U

IK hng, UP= UTR, iD= IDSS= K.UP

2 khi uGS = 0 (4.6)

JFET ch hot ng vi uGS m, khi uGS d-ng tip gip PN gia cc ca v knh dn phn cc thun, dng iG nhit phn cc thun, uGS s khng iu khin -c dng qua knh dn na. c tuyn V-A gia iG v uGS nh- trn hnh 4-12a: vng lm vic ca JFET l vng GS phn cc ng-c, iG = 0. iG iD IDSS Ch ngho

Vng lm vic uGS UP=UTR uGS

(a) c tuyn cc ca (b) c tuyn truyn dn Hnh 4-12 c tuyn V-A cc ca ca JFET.

c tuyn truyn dn ca JFET (hnh 4-12b) ct trc iD ti iD=IDSS khi uGS = 0. Vng lm vic l ch ngho ng vi uGS < 0

4-3 tranzito hiu ng tr-ng loi GaAsMESFET

MESFET (Metal Semiconductor FET) l tranzito hiu ng tr-ng c cc ca kim loi v knh bn dn.

GaAs l cht bn dn hp cht hai nguyn t gallium (nhmIII) v arsenic (nhm V) c c tnh ging silicon nh-ng c linh ng in t cao gp 5 ln so vi silicon v vy m tc chuyn trng thi t ct dng sang bo ho rt nhanh. Knh dn N ca GaAsMESFET -c lm t Gallium Arsenide. GaAsMESFET -c ng dng nhiu trong cc mch khuch i tn s cao, cc


Page 66

mch lgic tc cao. linh ng cc l trng trong GaAs thp nn loi MESFET knh dn P li t -c s dng.

Cu to v k hiu ca GaAsMESFET trn hnh 4-13. Cc ngun S v cc mng D -c ni vi cc khi bn dn loi N pha tp mnh v ni vi nhau qua knh dn N, trn phin GaAs khng pha tp c dn in rt thp, hnh thnh lp ngho m bo cch in gia cc cc, gim in dung k sinh nng cao tc cho GaAsMESFET. Lp kim loi gn vi cc ca th-ng l titanium hoc nhm. Tip gip kim loi- bn dn hnh thnh hng ro Schottky, lm vic nh- tip gip PN trong JFET. Kim loi hng ro Schottky S G D Cht tip xc Ohmic (a) K hiu: D G S

(b) Hnh 4-13 Cu to (a) v k hiu (b) ca GaAsMESFET

c tuyn V-A gn ging nh- JFET c in p ng-ng UTR m. im

khc so vi JFET l: trong GaAsMESFET c bo ho tc xy ra hu nh- trn ton b knh dn cn trong JFET ch xy ra trn on tht ca knh. V bo ho tc c mc in tr-ng thp trong GaAs nn linh ng cc in t trong GaAsMESFET cao. Mt im khc na ca GaAsMESFET l c knh dn ngn nn trong vng dng khng i iD vn ph thuc nh vo uDS, -ng c tuyn V-A dc hn (hnh 4-14). iD uGS=0 uGS


Page 67

uGS =UTR uDS

Hnh 4-14 c tuyn V-A cc mng ca GaAsMESFET c tuyn cng gm ba vng nh- JFET:

Vng ct dng uGSUTR (uGS d-ng hn UTR), uDS< (uGS-UTR) iD= K[2(uGS- UTR)uDS-u

2DS](1+uDS) (4.7)

Vng dng khng i khi uGS >UTR v uDS (uGS- UTR): iD= K(uGS- UTR)

2(1+uDS), (4.8) gi l h s iu ch knh dn c tr s 0,05 n 0,2 V-1. in p ng-ng UTRkhong 0,5 n 2,5V

4-4 Phn cc cho FET

Phn cc cho FET, chn im lm vic gia vng dng khng i. Cc gi tr ti hn cn l-u l im ct dng iD=0, vng trit, dng cc mng cc i IDmax v in p cho php cc i trn DS: UDS0.

Gi tr in p phn cc u vo UGG -c chn sao cho tn hiu ra i xng c bin cc i cn nm trong vng dng khng i. S phn cc tng qut cho FET nh- trn hnh 4-15.

RD

a G

b'

S

UGG

UDD

D

b

iG

+-

uGS

iD+

uDS-

iS

Q

(a)

Hnh 4-15 Phn cc cho MOSFET

Mch gm hai ngun UGG cung cp in p mt chiu cho cc ca v ngun UDD cung cp in p cho knh dn ngun-mng.

im lm vic Q(IGQ,UGSQ,IDQ,UDSQ) lun c IGQ = 0 v UGSQ -c xc nh tu theo cu trc mch phn cc u vo. Cc gi tr IDQ,UDSQ -c xc nh theo cu trc mch phn cc u ra. Trn c tuyn ra (c tuyn cc mng), im lm vic l giao im -ng ti vi -ng c tuyn tnh ng vi uGS = UGSQ(hnh 4-15b).

-ng ti theo s hnh 4-15:

iD

IDmax

UDS0 uDS

Q

UDSQ

IDQ uGS=UGSQ

Vng Trit

N

M

(b)

-ng ti


Page 68

D

DSDDD

R

uUi

(4.9)

im lm vic Q -c chn trong khong gia on MN ca -ng ti. Thc t c th to ra hai ngun UGGv UDD t mt ngun theo cc s thng

dng d-i y. 1. Phn cc bng phn p (MOSFETgiu)

im lm vic Q(IGQ,UGSQ,IDQ,UDSQ), vi: IG=0, nn: IGQ=0 (4.10)

Theo s hnh 4-16, in p GS lun bng in p phn p trn RB:

UGSQ= uGS = DDBA

B URR

R.

(4.11)

FET lm vic vng dng khng i: iD= K(uGS-UTR)2

IDQ= K(UGSQ-UTR)2 (4.12)

Theo s , ph-ng trnh -ng ti: uDS= UDD- iD.RD UDSQ= UDD- IDQ.RD (4.13)

+ UDD -

RA

RB

RD

Q

iS

iD

iG

+ uGS -

+

uDS-

G

Hnh 4-16 Phn cc bng phn p

Trong s , in p uGS lun d-ng nn mch ny ch p dng cho MOSFET giu knh dn N. 2. T phn cc(MOSFET ngho v JFET)


Page 69

+ UDD -

RG

RD

RS

Q

iS

iD

iG

+ uGS -

+

uDS-

Hnh 4-17 T phn cc

RG trong s hnh 4-17 c gi tr bt k do dng iG=0 nn in p trn n lun bng khng, khng nh h-ng n cc gi tr phn cc. Th-ng RG c gi tr

ln hng M n hng chc M. Khng c dng in cc ca nn theo 4.10: IGQ=0

Dng cc mng v cc ngun nh- nhau: iD=iS. in p trn GS bng in p trn RS gia t v cc ngun v khng c in p trn RG: UGSQ= -iSRS= -IDQRS (4.14)

Dng in cc mng lm vic ch dng khng i: IDQ=K(UGSQ- UTR)

2= K(IDQRS+ UTR)2 (4.15)

IDQ l nghim ca ph-ng trnh bc hai. Dng in cc mng ch c ngha khi c knh dn, chn nghim tho mn iu kin:

UGSQ > UTR, (4.16) in p cc ca d-ng hn gi tr ng-ng.

in p DS -c tnh theo -ng ti ca ra: UDSQ=UDD- IDQ(RD+RS) (4.17)

Trong tr-ng hp RS=0:

IGQ=0, UGSQ= 0 IDQ=K(- UTR )

2 UDSQ=UDD- IDQ .RD

in p uGS lun m nn mch ny ch p dng cho JFET v MOSFET ngho knh dn N. 3. Phn cc hi tip


Page 70

+ UDD -

RA

RB

RD

RS

Q

iS

iD

iG

+ uGS -

+

uDS-

G

Hnh 4-18 Phn cc hi tip

Nh- BJT, phn cc cho FET kt hp n nh im lm vic. Ph-ng php

phn cc hi tip c bn bng in p song song hoc dng in ni tip. Hnh 4-18 l phn cc hi tip dng in ni tip, vi:

UG= DDBA

B URR

R.

, (4.18)

uGS = UG- iSRS, iS = iD (4.19) UGSQ = UG - IDQRS (4.20)

Dng in cc ca bng khng: IGQ= 0 FET lm vic vng dng khng i: ID= K(uGS-UTR)

2, nh- 4.12: IDQ= K(UGSQ-UTR)

2 Thay gi tr UGSQ:

IDQ= K[(UG-UTR)-IDQ.RS]2 (4.21)

Gii ph-ng trnh bc hai: I2DQ.R

2S-IDQ[1/K +2 RS(UG-UTR)]+(UG-UTR)

2=0, (4.22) tnh -c IDQ, chn nghim tho mn: UGSQ d-ng hn UTR: UGSQ>UTR.

UDSQ=UDD- IDQ(RD+RS) Tr-ng hp RS ln: RS(UG-UTR)>>1/K th c th tnh gn ng:

I2DQ.R2S-2IDQ RS(UG-UTR)+ (UG-UTR)

2=0 IDQ= (UG-UTR)/ RS

Khi RS=0 th:

IDQ=K(UG-UTR)2

in p uGS c th m hoc d-ng tu thuc gi tr in p UG nn ph-ng php ny c th p dng cho tt c cc loi FET.

So vi BJT, FET c mt s c tnh khc bit sau:


Page 71

1. FET l cu kin iu khin bng in p, BJT iu khin bng dng in. FET thch hp vi nhng ngun tn hiu ch cung cp dng rt nh, BJT thch hp vi ngun tn hiu cung cp dng ln.

2. FET dn in ch nh cc phn t mang in a s, cc phn t dn in trong BJT gm c cc phn t thiu s ph thuc nhiu vo nhit v cc yu t nng l-ng bn ngoi nn FET lm vic n nh hn cc mi tr-ng khc nhau.

3. H s tp m ca FET nh hn BJT (do khng c tp m ti hp gia cc phn t mang in tri du) nn FET rt thch hp cho cc tng u vo tn hiu nh, c bit vi cc thit b yu cu tp m nh.

4. Cu trc FET i xng, cc cc D v S trong FET ging nhau, nn c th i ln -c cc D cho S. BJT c cc E hon ton khc cc C.

5. Do dng cc ca cch in thc t rt nh nn cng sut iu khin cc ca i vi FET rt nh, c th s dng -c trong cc mch cng sut nh, rt thch hp cho ch to cc mch tch hp (IC). Hn na, tr khng vo ca FET rt ln nn c th thch ng vi nhiu loi ngun tn hiu.

4.5. Thyristor

4.5.1. Diode Shockley

a. Cu to, k hiu

Diode Shockley l mt linh kin bn dn c cu trc gm 4 lp bn dn p-

n-p-n xen k vi nhau, kt hp vi 2 in cc: Cc Anode (A) v cc Cathode

(K). Diode Shockley hot ng nh mt chuyn mch on_off v s tn ti

mt trng thi sau mi ln c kch m hoc ngt.

b. Nguyn l hot ng

A

K

p+

p++

n

n++

p

p

n

n

A

K

J1

J2

J3


Page 72

0AKU : Khi AKU nh , tip gip J1 v J3 c phn cc ngc, khi

dng qua diode Shockley l dng r ngc 0DI , min c tuyn ng vi iu

kin ny c gi l min chn ngc. Nu UAK tng n mt gi tr in p

nh thng ngc th tip gip J1 v J3 ln lt b nh thng, dng qua diode

tng mnh.

0AKU : Tip gip J2 c phn cc ngc nn dng qua diode

Shockley l dng ngc bo ha 0DI , cp Transistor ch ngt, min c

tuyn tng ng c gi l min chn thun. Tng in p UAK n gi tr

ln nh thng tip gip J2, khi diode bt u thng (on), gi tr UAK ti

im c gi l in p nh thng thun (Breakover Voltage). Tuy nhin

trong cu trc ca diode Shockley c s hi tip dng nn cng dng qua

diode Shockley tng mnh v a cp Transistor vo trng thi bo ha. Khi

diode Shockley tng ng vi mt in tr thun c gi tr nh do in p

UAK gim t ngt. Nu tip tc tng in p UAK khi diode Shockley s hot

ng nh mt in tr thun. Min c tuyn khi c gi l min dn

thun a diode Shockley tr v trng thi ngt phi gim in p UAK sao

cho dng qua diode ID nh hn dng duy tr IH.

Ngoi ra, c th kch m diode Shockley bi mt xung c bin thin

dtdu ln. Do cc in dung tip gip k sinh trong mi Transistor chng li

s thay i in p gy nn dng in ln kch m cho diode Shockley.

Do diode Shockley ch tn ti ti mt trng thi sau mi ln c kch m

hoc ngt nn c th coi diode Shockley nh mt ci cht (latch).

4.5.2. Diac

Diac l linh kin bn dn gm 2 diode Shockley c ghp song song

nhng ngc chiu nhau nn c th dn dng theo c 2 chiu. Diac c 2 in p

ngng nh thng, c kch m 1 ln trong mi na chu k. Mi ln ngun

xoay chiu o cc tnh, Diac ngt dng (off) ti thi im Diac c kch m

trong na chu k tip theo, khi Diac chuyn sang trng thi thng (on).


Page 73

4.5.3. SCR

a. Cu to:SCR (Silicon Controlled Rectifier - Chnh lu c iu khin) c

cu trc ging diode Shockley nhng c thm cc ca G (Gate) ng vai tr l

cc iu khin.

b. Nguyn l hot ng

0AKU : c tuyn Volt_Ampere ca SCR trong min ny tng t

vi c tuyn ca diode Shockley.

A A

K G

p+

p++

n

n++

p

n n p p

n

G

K

A

p

p

n

n

A

G

K

J1

J2

J3

G

T1

T2

K

IC2=2.IB2

IB1

IC1

IB2

Dng qua Diac

in p ngun


Page 74

0AKU

Nu 0GV : SCR hot ng nh mt diode Shockley.

Nu 0GV , xut hin dng cc ca IG cng chiu vi dng

ngc bo ha trong SCR do tip gip J2 b nh thng vi in p UAK nh

hn nhiu so vi trng hp 0GV ; c th ni in p VG iu khin in p

ngng nh thng UBO. in p GV cng ln th in p UBO cng nh. Sau

khi c kch m, cc ca G mt vai tr iu khin v SCR s dn cho n khi

dng qua SCR nh hn dng duy tr IH.

Vy c th kch m Thyristor theo 2 cch: tng in p UAK hoc cp mt

in p ti cc ca G bi mt xung c nng lng rt nh. iu ny th hin c

tnh khuch i cng sut ca mch chnh lu s dng SCR.

c. ng dng

Do ch dn dng theo mt chiu nn SCR cng c ng dng trong cc

mch chnh lu. im khc bit ca SCR so vi Diode chnh lu thng thng

l c th iu khin c gc pha ca tn hiu ra trn ti (iu

khin cng sut trn ti). Ngy nay, SCR l mt trong nhng linh kin

chnh lu c nhy tt nht.

Xt mch chnh lu c iu khin n gin nht. Diode D c tc dng bo

v SCR trong na chu k m.

Ban u, SCR ngt, in p trn ti 0Lu . Sau , in p dng c

a ti cc ca G ( 0GKU ), SCR c kch m ti gi tr in p BOs Uu

tng ng vi mt gi tr UGK xc nh. Khi SCR tng ng vi mt in

tr thun c gi tr rt nh, nn in p trn ti sL uu . C th mc thm

bin tr VR iu chnh in p UGK, tc l iu chnh in p ngng nh

thng UBO nn c th iu khin c gc pha ti SCR c kch m.

RL

uS us

uL


Page 75

Tuy nhin, i vi s mch nh trn th SCR c th c kch m ti

gc pha ln nht l /2, do ti thi im us t gi tr cc i nu SCR vn

cha c kch m th khng th kch m ti gc pha ln hn. Mch trn cn

c gi l mch khng ch pha 900.

Vy mun kch m SCR ti gc pha ln hn /2 c th mc thm t in C.

GKDC uuu

in p uC dch pha so vi in p ngun mt gc trong khong ( 20 ),

ng vai tr ging in p ngun a in p dng ti cc ca G, nn c th

kch m SCR ti gc pha bt k trong khong ( 0 ) v c gi l mch

khng ch pha 1800.

4.5.4. Triac

a. Cu to

Triac l mt linh kin bn dn gm 2 SCR c ghp song song nhng

ngc chiu, 2 cc ca c ni vi nhau. i vi Triac, khng cn cc Anode

Ngng nh thng RL

us

VR

us

uL

RL VR

us C SCR

D

uL Ngng kch

uC

Ngng nh thng


Page 76

v Cathode m thay vo l 2 cc chnh MT1 v MT2 (Main Terminal). Cc G

vn ng vai tr l cc iu khin.

b. Nguyn l hot ng

Triac tng ng vi mt cp SCR nn c kh nng dn dng theo c 2

chiu. Tng ng vi mi gi tr ca in p cc ca VG, Triac s c 2 ngng

nh thng khng i xng. Khi , Triac c kch m mt ln

trong mi na chu k. Tuy nhin, vai tr ca 2 cc MT1 v MT2 l khng

ging nhau. Dng kch cc ca G phi c a t cc MT2.

c.ng dng

Khc vi SCR c ng dng trong cc mch cng sut ln, Triac c

s dng trong mt s mch cng sut nh, v d nh chuyn mch n bo hiu

trong gia nh. Khu di pha RC c tc dng kch m Triac ti mt gi tr gc pha

bt k trong khong ( 0 ).

n

us

n

us


Page 77

Tuy nhin, do Triac c kch m ti cc in p ngng khng i xng

gy nn cc thnh phn hi trong dng sng u ra, do thng Diac c mc

thm vo mch nh sau:

4.5.5. UJT (UNIJUNCTION TRANSISTOR TRANSISTOR N NI).

Transistor thng (BJT) gi l Transistor lng cc v c hai ni PN trong

lc UJT ch c mt c nht ni P-N. Tuy khng thng dng nh BJT, nhng

UJT c mt s c tnh c bit nn mt thi gi vai tr quan trng trong cc

mch to dng sng v nh gi.

1. Cu to v c tnh ca UJT:

Hnh sau y m t cu to n gin ho v k hiu ca UJT

Mt thi bn dn pha nh loi n- vi hai lp tip xc kim loi hai u

to thnh hai cc nn B1 v B2. Ni PN c hnh thnh thng l hp cht ca

dy nhm nh ng vai tr cht bn dn loi P. Vng P ny nm cch vng B1

khong 70% so vi chiu di ca hai cc nn B1, B2. Dy nhm ng vai tr

cc pht E.

K hiu ca Transistor mt tip gip UJT nh trong hnh B09.2 a v b.

n

us


Page 78

Hnh B09.1. Hnh B09.2.

Tr khng gia base 1 v base 2 c o khi dng emitter =0 c gi l

tr khng gia cc base (interbase) RBB v c gi tr in hnh khong 5K

10 K Ohm.

Hnh B09.3 ch ra mch tng ng n gin ca UJT vi cc Base loi

N. Tr khng RBB c phn i bi chuyn tip P-N (biu th bi diode) thnh

2 in tr RB1 v RB2 , m tng ca n bng RBB .

Trong ch hot ng thng thng, in p VBB c cung cp cho

base 1 v base 2, vi base 2 dng hn so vi 1. Khi khng c dng IE , thanh

bn dn s hot ng ging nh mt b phn p n gin v c mt phn in p

xc nh ca VBB xut hin trn RB1. T s n c gi l t s cn bng

(stand-off) ni v gi tr ca n khong khong 0,5 n 0,9 . T s ny c cho

bi:

in p VBB khin cathode ca d

giao trinh linh kien dien tu gtvt

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