gt dien tu co ban 572
DESCRIPTION
Gt Dien Tu Co BanTRANSCRIPT
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B LAO NG - THNG BINH V X HI TNG CC DY NGH
D n Gio dc K thut v Dy ngh (VTEP)
GIO TRNH
5
H Ni - 2007
Mn hc: IN T C BN M s: CIE 0109 00
NGH SA CHA THIT B IN CNG NGHIP
Trnh : Lnh ngh
Logo
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2
(Mt sau trang ba)
M tI liu:
M quc t ISBN:..
Tuyn b bn quyn:
Ti liu ny thuc loi sch gio trnh Cho nn cc ngun thng tin c th c php dng nguyn bn hoc trch dng cho cc mc ch v o to v tham kho . Mi mc ch khc c lch lc hoc s dng vi mc ch kinh doanh thiu lnh mnh s b nghim cm. Tng Cc Dy ngh s lm mi cch bo v bn quyn ca mnh.
Tng Cc Dy Ngh cm n v hoan nghnh cc thng tin gip cho vic tu sa v hon thin tt hn tI liu ny.
a ch lin h: D n gio dc k thut v ngh nghip Tiu Ban Pht trin Chng trnh Hc liu ................................................................
..
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LI TA
(Vi nt gii thiu xut x ca chng trnh v ti liu)
Ti liu ny l mt trong cc kt qu ca D n GDKT-DN ..
(Tm tt ni dung ca D n)
(Vi nt gii thiu qu trnh hnh thnh ti liu v cc thnh phn tham gia)
(Li cm n cc c quan lin quan, cc n v v c nhn tham gia)
(Gii thiu ti liu v thc trng)
Ti liu ny c thit k theo tng m un/ mn hc thuc h thng m
un/mn hc ca mt chng trnh, o to hon chnh Ngh Sa cha thit b
in cng nghip cp trnh lnh ngh v c dng lm Gio trnh cho hc
vin trong cc kho o to, cng c th c s dng cho o to ngn hn hoc
cho cc cng nhn k thut, cc nh qun l v ngi s dng nhn lc tham kho.
y l ti liu th nghim s c hon chnh tr thnh gio trnh chnh
thc trong h thng dy ngh.
H ni, ngy ... thng. nm....
Gim c D n quc gia
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MC LC
TT NI DUNG TRANG
1 Li ta
..........................................................................................................
3
2 MC
LC..........................................................................................................
4
3 GII THIU V MN
HC...................................................................................
5
4 S quan h theo trnh t hc
ngh...........................................................
6
5 CC HNH THC HOT NG HC TP CHNH TRONG
MN HC................................
8
6 BI 1: CC KHI NIM C
BN.........................................................................
9
7 Bi 2: Lnh kin th
ng..............................................................................
21
8 BI 3: LINH KIN BN
DN...............................................................................
38
9 BI 4: CC MCH KHUCH I DNG TRANZTOR
................................................
71
10 Bi 5: Mch ng dng dng
BJT..................................................................
99
11 TR LI CC CU HI V BI
TP........................................................................
121
12 TI LIU THAM
KHO.........................................................................................
129
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GII THIU V M UN/MN HC
V tr, ngha, vai tr m un/mn hc:
Vi s pht trin v hon thin khng ngng ca thit b in trn mi lnh
vc i sng x hi, mch in t tr thnh mt thnh phn khng th thiu c
trong cc thit b in, cng dng chnh ca n l iu khin khng ch cc thit
b in, thay th mt s kh c in c nhy cao. Nhm mc ch: gn ha cc
thit b in, gim tiu hao nng lng trn thit b, tng nhy lm vic, tng tui
th ca thit b....Do , nhn dng c cc linh kin, mch in t, kim tra, thay
th, c cc linh kin, mch in h hng l mt yu cu quan trng khng th
thiu c, nht l trong lnh vc in t cng nghip, khi m cc dy chuyn cng
nghip c hnh thnh v pht trin mnh trn phm vi c nc.
Mc tiu thc hin ca mn hc:
Sau khi hon tt mn hc ny, hc vin c nng lc:
Phn bit c hnh dng, k hiu, cu to, nguyn l lm vic ca cc linh
kin in t thng dng theo cc tiu chun c hc.
ng dng cc linh kin in t, mch in t c bn v thc t theo yu
cu k thut.
S dng my o VOM phn loi, o kim tra xc nh cht lng linh
kin v mch in t c bn trong cng nghip theo cc c tnh
linh kin v mch in t
Ni dung chnh ca mn hc:
Mn hc ny c nm bi, hc trong 90 gi, trong 40 gi l thuyt v 50 gi
thc hnh. Cc bi hc nh sau:
Bi 1: Cc khI nim c bn
Bi 2: Linh kin th ng
Bi 3: Linh kin bn dn
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Bi 4: Cc mch khuych i dng tranzito
Bi 5: Cc mch ng dng dng tranzito
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2.4. S MI LIN H GIA CC M-UN V MN HC TRONG CHNG TRNH
CHNH TR - 01
PHP LUT - 02
TH CHT - 03
Q. PHNG - 04
TIN HC - 05
ANH VN - 06
ATL - 07
KH C IN - 14
VT LIU IN -13
K THUT IN - 08
K THUT NGUI - 12
V KT C KH- 10
T-H TRANG B IN 1 - 22
IN T NG DNG - 23
K-THUT CM BIN -
24
K THUT S - 25
TRANG B IN 1 - 21
Q -DY MY IN -18
CUNG CP IN 1 - 19
MY IN -17
TRANG B N 2 - 26
PLC C BN -27
THC TP SN SUT
U RA
MT M-UN B TR
O LNG IN 1 - 16
V IN - 11
THIT B IN GD - 15
IN T C BN - 09
KT LP T IN - 20
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Ghi ch:
Mn hc in t c bn cung cp nhng kin thc c s hc vin c th phn tch hot ng, lp rp v sa cha ca cc
mch in ttng thit b in, Kh c in. Mn hc ny c tm quan trng khng th thiu c trong phn o to tay ngh cho
cng nhn hot ng trong lnh vc in.
Khi hc vin hc tp v thc hnh mn hc ny, nu phn no khng t yu cu, cn phi c hc li v kim tra kin thc v
thc hnh v phn cha t .
Khi chuyn trng, chuyn ngnh, hc vin nu hc mt c s o to khc ri th phi xut trnh giy chng nhn; Trong
mt s trng hp c th vn phi qua st hch li.
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CC HOT NG HC TP CHNH TRONG MN HC
Hot ng hc trn lp c tho lun.
Hot ng t hc, t su tm cc ti liu lin quan v lm cc bi tp v mn
hc in t c bn.
Hot ng thc hnh ti xng v cc mch in t c bn hc, lp rp v
pht hin nhng sai li ca cc mch in t c bn.
YU CU V NH GI HON THNH MN HC
Ni dung kim tra vit:
Trnh by cu to, nguyn l hot ng, ng dng cc linh kin in t c bn.
Trnh by ng dng ca cc mch in t c bn.
Phn tch cc mch in t c bn.
Ni dung kim tra thc hnh:
Kim tra k nng thc hnh lp rp, sa cha, thay th cc linh kin c nh
gi theo cc tiu chun:
- chnh xc ca cc dng tn hiu ng ra, sau khi lp rp, sa cha.
- Tnh thm m ca mch lp rp, sa cha .
Cc vt liu khi thc hnh:
Cc linh kin in t th ng v bn dn cc loi theo yu cu mch in thc
t
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BI 1
CC KHI NIM C BN
M BI: CIE 01 09 01
GII THIU:
Nn tng c s ca h thng in ni chung v in k thut ni ring xoay
quanh vn dn in, cch in ca vt cht gi l vt liu in. Do hiu c
bn cht ca vt liu in, vn dn in v cch in ca vt liu, linh kin l mt
ni dung khng th thiu c trong kin thc ca ngi th in, in t. chnh
l ni dung ca bi hc ny.
MC TIU THC HIN:
Hc xong bi hc ny, hc vin c nng lc:
nh gi / xc nh tnh dn in trn mch in, linh kin ph hp theo yu
cu k thut.
Pht biu tnh cht, iu kin lm vic ca dng in trn cc linh kin in t
khc nhau theo ni dung hc.
Tinh ton in tr, dng in, in p trn cc mch in mt chiu theo iu
kin cho trc.
NI DUNG:
Vt dn in v cch in
Cc ht mang in v dng in trong cc mi trng
HOT NG I: HC L THUYT TRN LP
1.1.Vt dn in v cch in:
1.1.1 Vt dn in v cch in: Trong k thut ngi ta chia vt liu thnh hai
loi chnh:
Vt cho php dng in i qua gi l vt dn in
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Vt khng cho php dng in i qua gi l vt cch in
Tuy nhin khi nim ny ch mang tnh tng i. Chng ph thuc vo cu to
vt cht, cc iu kin bn ngoi tc ng ln vt cht
V cu to: vt cht c cu to t cc nguyn t. Nguyn t c cu to gm
hai phn chnh l ht nhn mang in tch dng (+) v cc electron mang in tch
m e-- gi l lp v ca ngyn t. Vt cht c cu to t mi lin kt gia cc
nguyn t vi nhau to thnh tnh bn vng ca vt cht. Hnh1.1
Hnh 1.1: Cu trc mng lin kt nguyn
t ca vt cht
Cc lin kt to cho lp v ngoi cng c 8 e--, vi trng thi nguyn t mang
tnh bn vng v c gi l trung ho v in. Cc cht loi ny khng c tnh dn
in, gi l cht cch in
Cc lin kt to cho lp v ngoi cng khng 8 e--, vi trng thi ny chng
d cho v nhn in t, cc cht ny gi l cht dn in
V nhit mi trng: Trong iu kin nhit bnh thng (< 250C) cc
nguyn t lin kt bn vng. Khi tng nhit , ng nng trung bnh ca cc nguyn
t gia tng lm cc lin kt yu dn, mt s e-- thot khi lin kt tr thnh e-- t do,
lc ny nu c in trng ngoi tc ng vo, vt cht c kh nng dn in.
V in trng ngoi: Trn b mt vt cht, khi t mt in trng hai bn
chng s xut hin mt lc in trng E. Cc e-- s chu tc ng ca lc in trng
ny, nu lc in trng ln, cc e-- s chuyn ng ngc chiu in trng, to
thnh dng in. ln ca lc in trng ph thuc vo hiu in th gia hai
im t v dy ca vt dn.
Tm li: S dn in hay cch in ca vt cht ph thuc nhiu vo 4 yu t:
Cu to nguyn t ca vt cht
Nhit ca mi trng lm vic
Hiu in th gia hai im t ln vt cht
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dy ca vt cht
a. Vt dn in: Trong thc t, ngi ta coi vt liu dn in l vt cht trng
thi bnh thng c kh nng dn in. Ni cch khc, l cht trng thI bnh
thng c sn cc in tch t do to thnh dng in
Cc c tnh ca vt liu dn in l:
- in tr sut
- H s nhit
- Nhit nng chy
- T trng
Cc thng s v phm vi ng dng ca cc vt liu dn in thng thng c
gii thiu trong Bng 1.1:
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BNG 1.1: VT LIU DN IN
tt
Tn vt liu
in tr
sut
mm2/m
H s
nhit
Nhit
nng
chy
t0C
T
trng
Hp kim
Phm vi ng dng
Ghi ch
1 ng hay
ng k
thut
0,0175 0,004 1080 8,9 Ch yu dng lm dy dn
2 Thau (0,03 -
0,06)
0,002 900 3,5 ng vi
km
- Cc l tip xc
- Cc u ni dy
3 Nhm 0,028 0,0049 660 2,7 - Lm dy dn in
- Lm l nhm trong t
xoay
- Lm cnh to nhit
- Dng lm t in (t ho)
- B xyt ho nhanh, to
thnh lp bo v, nn kh
hn, kh n mn
- B hi nc mn n
mn
4 Bc 960 10,5 - M v ngoi dy dn
s dng hiu ng mt
ngoi trong lnh vc siu
cao tn
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5 Nic ken 0,07 0,006 1450 8,8 - M v ngoi dy dn
s dng hiu ng mt
ngoi trong lnh vc siu
cao tn
C gi thnh r hn bc
6 Thic 0,115 0,0012 230 7,3 Hp cht
dng lm
cht hn
gm:
- Thic 60%
- Ch 40%
- Hn dy dn.
- Hp kim thic v ch c
nhit nng chy thp
hn nhit nng chy
ca tng kim loi thic v
ch..
Cht hn dng hn
trong khi lp rp linh kin
in t
7 Ch 0,21 0,004 330 11,4 - Cu ch bo v qu dng
- Dng trong ac qui ch
- V bc cp chn
Dng lm cht hn (xem
phn trn)
8 St 0,098 0,0062 1520 7,8 - Dy st m kem lm dy
dn vi ti nh
- Dy lng kim gm li
st v bc ng lm dy
dn chu lc c hc ln
- Dy st m km gi
thnh h hn dy ng
- Dy lng kim dn in
gn nh dy ng do c
hiu ng mt ngoi
9 Maganin 0,5 0,00005 1200 8,4 Hp cht
gm:
- 80% ng
Dy in tr
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15
- 12%
mangan
- 2% nic ken
10 Contantan 0,5 0,000005 1270 8,9 Hp cht
gm:
- 60% ng
- # 40% nic
ken
- # 1%
Mangan
Dy in tr nung nng
11 Niken -
Crm
1,1 0,00015 1400
(nhit
lm
vic:
900)
8,2 Hp cht
gm:
- 67%
Nicken
- 16% st
- 15% crm
- 1,5%
mangan
- Dng lm dy t nng
(dy m hn, dy bp
in, dy bn l)
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Cc c tnh ca vt liu cch in gm:
- bn v in.
- Nhit chu ng.
- Hng s in mi.
- Gc tn hao.
- T trng.
Cc thng s v phm vi ng dng -c trnh by Bng 1.2:
1.2 in tr cch in ca linh kin v mch in t:
- in tr cch in ca mch in l in tr khi c in p ln nht cho
php t vo gia m linh kin khng b nh thng (phng in).
Cc linh kin c gi tr in p ghi trn thn linh kin km theo cc i
l-ng c tr-ng.
V d: T in -c ghi trn thn nh- sau: 47/25vV, c ngha l
Gi tr l 47 v in p ln nht c th chu ng -c khng qu 25v.
Cc linh kin khng ghi gi tr in p trn thn th-ng c tc dng cho
dng in mt chiu (DC) v xoay chiu (AC) i qua nn in p nh thng
c t-ng quan vi dng in nn th-ng -c ghi bng cng sut.
V d: in tr -c ghi trn thn nh- sau: 100/ 2W C ngha l
Gi tr l 100 v cng sut chu ng trn in tr l 2W, chnh l t s
gia in p t ln hai u in tr v dng in i qua n (U/I). U cng ln
th I cng nh v ng-c li.
Cc linh kin bn dn do cc thng s k thut rt nhiu v kch th-c li
nh nn cc thng s k thut -c ghi trong bng tra m khng ghi trn thn
nn mun xc nh in tr cch in cn phi tra bng.
in tr cch in ca mch in l in p ln nht cho php gia hai
mch dn t gn nhau m khng sy ra hin t-ng phng in, hay dn
in. Trong thc t khi thit k mch in c in p cng cao th khong
cch gia cc mch in cng ln. Trong sa cha th-ng khng quan tm
n yu t ny tuy nhin khi mch in b m -t, b bi m... th cn quan
tm n yu t ny trnh tnh trng mch b dn in do yu t mi tr-ng.
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1.2. Cc ht mang in v dng in trong cc mi tr-ng:
1.2.1. Khi nim ht mang in:
Ht mang in l phn t c bn ca vt cht c mang in, ni cch
khc l cc ht c s ca vt cht m c tc dng vi cc lc in tr-ng,
t tr-ng.
Trong k thut tu vo mi tr-ng m tn ti cc loi ht mang in
khc nhau, Chng bao gm cc loi ht mang in chnh sau:
- e-- (electron) L cc in tch nm lp v ca nguyn t cu to nn
vt cht, khi nm lp v ngoi cng lc lin kt gia v v ht nhn yu d
bt ra khi nguyn t to thnh cc ht mang in trng thi t do d
dng di chuyn trong mi tr-ng.
- ion+ L cc nguyn t cu to nn vt cht khi mt in t lp ngoi
cng chng c xu h-ng ly thm in t tr v trng thi trung ho v
in nn d dng chu tc dng ca lc in, nu trng thi t do th d
dng di chuyn trong mi tr-ng.
- ion-- L cc nguyn t cu to nn vt cht khi tha in t lp ngoi
cng chng c xu h-ng cho bt in t tr v trng thi trung ho v in
nn d b tc dng ca cc lc in, nu trng thi t do th chng d dng
chuyn ng trong mi tr-ng.
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BNG 1.2: VT LIU CCH IN
TT
Tn vt liu
bn v
in
(kV/mm)
t0C
chu
ng
Hng s
in mi
Gc tn
hao
T
trng
c im
Phm vi ng dng
1 Mi ca 50-100 600 6-8 0,0004 2,8 Tch c thnh
tng mnh rt
mng
- Dng trong t in
- Dng lm vt cch in trong thit
b nung nng (VD:bn l)
2 S 20-28 1500-
1700
6-7 0,03 2,5 - Gi cch in cho ng dy
dn
- Dng trong t in, n, ct
cun dy
3 Thu tinh 20-30 500-
1700
4-10 0,0005-
0,001
2,2-4
4 Gm khng
chu c
in p
cao
khng
chu
c
nhit
ln
1700-
4500
0,02-0,03 4 - Kch thc nh
nhng in dung
ln
- Dng trong t in
5 Baklit 10-40 4-4,6 0,05-0,12 1,2
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6 bnit 20-30 50-60 2,7-3 0,01-
0,015
1,2-1,4
7 Pretspan 9-12 100 3-4 0,15 1,6 Dng lm ct bin p
8 Giy lm t
in
20 100 3,5 0,01 1-1,2 Dng trong t in
9 Cao su 20 55 3 0,15 1,6 - Lm v bc dy dn
- Lm tm cch in
La cch
in
8-60 105 3,8-4,5 0,04-0,08 1,5 Dng trong bin p
Sp 20-25 65 2,5 0,0002 0,95 Dng lm cht tm sy bin p, ng
c in chng m
Paraphin 20-30 49-55 1,9-2,2 Dng lm cht tm sy bin p, ng
c in chng m
Nha thng 10-15 60-70 3,5 0,01 1,1 - Dng lm sch mi hn
- Hn hp paraphin v nha thng
dng lm cht tm sy bin p, ng
c in chng m
poxi 18-20 1460 3,7-3,9 0,013 1,1-1,2 Hn gn cc b kin in-in t
Cc loi
plastic
(polyetylen,
Dng lm cht cch in
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20
polyclovinin)
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21
1.2.2 Dng in trong cc mi trng:
Dng in l dng chuyn di c hng ca cc ht mang in di tc dng ca
in trng ngoi.
a. Dng in trong kim loi: Do kim loi th rn cu trc mng tinh th bn vng
nn cc nguyn t kim loi lin kt bn vng, ch c cc e- trng thi t do. Khi c in
trng ngoi tc ng cc e- s chuyn ng di tc tc dng ca lc in trng to
thnh dng in.
Vy: Dng in trong kim loi l dng chuyn ng c hng ca cc e- di tc
dng ca in trng ngoi.
Trong k thut in ngi ta qui c chiu ca dng in l chiu chuyn ng ca
cc ht mang in dng nn dng in trong kim loi thc t ngc vi chiu ca dng
in qui c.
b. Dng in trong cht in phn:
Cht in phn l cht dng dung dch c kh nng dn in c gi l cht in
phn. Trong thc t cht in phn thng l cc dung dch mui, axit, baz.
Khi dng dung dch (ho tan vo nc) chng d dng tch ra thnh cc ion tri
du. Vi d: Phn t NaCl khi ho tan trong nc chng tch ra thnh Na+ v Cl- ring r.
Qu trnh ny gi l s phn li ca phn t ho tan trong dung dch.
Khi khng c in trng ngoi cc ion chuyn ng hn lon trong dung dch gi
l chuyn ng nhit t do. Khi c in trng mt chiu ngoi bng cch cho hai in
cc vo trong bnh in phn cc ion chu tc dng ca lc in chuyn ng c hng
to thnh dng in hnh thnh nn dng in trong cht in phn. S m t hot
ng c trnh by hnh 1.2
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22
Hnh 1.2: Dng in trong cht in phn
Cc ion+
chuyn ng cng chiu in trng v cc m, cc ion- chuyn ng
ngc chiu in trng v cc dng v bm vo bn cc. Li dng tnh cht ny ca
cht in phn m trong thc t ngi ta dng m kim loi, c kim loi.
Vy: Dng in trong cht in phn l dng chuyn di c hng ca cc ion
dng v m di tc dng ca in trng ngoi.
c. Dng in trong cht kh:
Cht kh l hn hp nhiu loi nguyn t hay phn t kh kt hp tn ti trong mi
trng.
trng thi bnh thng cc nguyn t, phn t trung ho v in. V vy cht kh
l in mi. cht kh tr thnh cc ht mang in ngi ta dng ngun nng lng t
bn ngoi tc ng ln cht kh nh t nng hoc bc x bng tia t ngoi hoc tia Rn
ghen Mt s nguyn t hoc phn t kh mt in t lp ngoi tr thnh in t t do
v cc nguyn t hoc phn t mt in t tr thnh cc ion+ , ng thi cc in t t do
c th lin kt vi cc nguyn t hoc phn t trung ho tr thnh cc ion- . Nh vy
lc ny trong mi trng kh s tn ti cc thnh phn nguyn t hoc phn t kh trung
ho v in, ion+ , ion- . Lc ny cht kh c gi b ion ho.
Khi khng c in trng ngoi cc ht mang in chuyn ng t do hn lon gi
l chuyn ng nhit khng xut hin dng in.
Khi c in trng ngoi ln cc ion v in t t do chu tc dng ca in
trng ngoi to thnh dng in gi l s phng in trong cht kh.
Vy: Dng in trong cht kh l dng chuyn di c hng ca cc ion dng, m
v cc in t t do, di tc dng ca in trng ngoi.
Cc ion dng chuyn ng cng chiu in trng, cc ion m v in t t do
chuyn ng ngc chiu in trng ngoi. S m t th nghim c trnh by
hnh 1.3:
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23
Hnh 1.3: S m t th nghim dng in trong cht kh.
p sut thp cht kh d b ion ho to thnh dng in gi l dng in trong
kh km. Trong k thut ng dng tnh cht dn in trong kh km m ngi ta ch to
nn n neon v mt s loi n khc, c bit trong k thut in t ngi ta ch to ra
cc n chng i cao p cc ni c in p cao gi l (spac).
d. Dng in trong chn khng:
Chn khng l mi trng hon ton khng c nguyn t kh hoc phn t kh c
ngha p sut khng kh trong mi trng = 0 at (at : atmt phe l n v o lng ca p
sut). Trong thc t khng th to ra c mi trng chn khng l tng. Mi trng
chn khng thc t c p sut khong 0,001 at, lc ny s lng nguyn t, phn t kh
trong mi trng cn rt t c th chuyn ng t do trong mi trng m khng sy ra s
va chm ln nhau. to ra c mI trng ny trong thc t ngi ta ht chn khng
ca mt bnh kn no , bn trong t sn hai bn cc gi l Anod v katot.
Khi t mt in p bt k vo hai cc th khng c dng in I qua v mi trng
chn khng l mi trng cch in l tng.
Khi si nng catt bng mt ngun in bn ngoi th trn b mt catt xut hin
cc e- bc x t catt.
Khi t mt in p mt chiu (DC) tng i ln khong vi trm votl vo hai cc
ca bnh chn khng. Vi in p m t vo Anod v in p Dng t vo catt th
khng xut hin dng in.
Khi i chiu t in p; Dng t vo Anod v m t vo catt th xut hin
dn in I qua mi trng chn khng trong bnh. Ta ni c dng in trong mi
-
24
trng chn khng l cc e- bc x t catt di chuyn ngc chiu in trng v
Anod.
Vy: Dng in trong mI trng chn khng l dng chuyn di c hng ca cc
e- di tc dng ca in trng ngoi.
Trong k thut, dng in trong chn khng c ng dng ch to ra cc n
in t chn khng, hin nay vi s xut hin c linh kin bn dn n in t chn
khng tr nn lc hu do cng knh d v khi rung sc va p, tn hao cng sut ln,
in p lm vic cao. Tuy nhin trong mt s mch in c cng sut cc ln, tng tr
lm vic cao,hay cn c pht sng trong qua trnh lm vic th v phi dng n in t
chn khng. Nh n hinh, n cng sut.
e. Dng in trong cht bn dn:
Cht bn dn l cht nm gia cht cch in v cht dn in, cu trc nguyn t
c bn in t lp ngoi cng nn d lin kt vi nhau to thnh cu trc bn vng.
ng thi cng d ph v di tc dng nhit to thnh cc ht mang in.
Khi b ph v cc mi lin kt, chng tr thnh cc ht mang in dng do thiu
in t lp ngoi cng gi l l trng. Cc in t lp v d dng bt khi nguyn t
tr thnh cc in t t do.
Khi t in trng ngoi ln cht bn dn cc e- chuyn ng ngc chiu in
trng, Cc l trng chuyn ng cng chiu in trng to thnh dng in trong
cht bn dn.
Vy: dng in trong cht bn dn l dng chuyn di c hng ca cc e- v cc
l trng di tc dng ca in trng ngoi.
Cht bn dn c trnh by trn c gi l cht bn dn thun khng c ng
dng trong k thut v phi c cc iu kin km theo nh nhit in p... khi ch to
linh kin. Trong thc t ch to linh kin bn dn ngi ta dng cht bn dn pha thm
cc cht khc gi l tp cht to thnh cht bn dn loi P v loi N
Cht bn dn loi P l cht bn dn m dng in ch yu trong cht bn dn l cc
l trng nh chng c pha thm vo cc cht c 3 e- lp ngoi cng nn chng thiu
in t trong mi lin kt ho tr to thnh l trng trong cu trc tinh th.
Cht bn dn loi N l cht bn dn m dng in ch yu l cc e- nh c pha
thm cc tp cht c 5 e- lp ngoi cng nn chng tha in t trong mi lin kt ho
tr trong cu trc tinh th to thnh cht bn dn loi N c dng in i qua l cc e- .
Linh kin bn dn trong k thut c cu to t cc mi lin kt P, N. T cc mi
ni P, N ny m ngi ta c th ch to c rt nhiu loi linh kin khc nhau. Tuyt i
-
25
a s cc mch in t hin nay u c cu to t linh kin bn dn, cc linh kin c
ch to c chc nng c lp nh Dit, tran zitor c gi l cc linh kin n hay linh
kin ri rc, cc linh kin bn dn c ch to kt hp vi nhau v vi cc linh kin
khc thc hin hon chnh mt chc nng no v c ng kn thnh mt khi
c gi l mch t hp (IC: Integrated Circuits). Cc IC c s dng trong cc mch
tn hiu bin i lin tc gi l IC tng t, cc IC s dng trong cc mch in t s
c gi l IC s. Trong k thut hin nay ngoi cch phn chia IC tng t v IC s
ngi ta cn phn chia IC theo hai nhm chnh l IC hn xuyn l v IC hn b mt
SMD: Surface Mount Device, Chng khc nhau v kch thc v nhit chu ng trn
linh kin. Xu hng pht trin ca k thut in t l khng ngng ch to ra cc linh
kin mi, mch in mi trong ch yu l cng ngh ch to linh kin m nn tng l
cng ngh bn dn.
CU HI V BI TP:
Cu hi trc nghim:
Hy la chn phng n ng tr li cc cu hi di y bng cch t en
vo vung thch hp:
TT Ni dung cu hi a b c d
1.1 Th no l vt dn in?
a. Vt c kh nng cho dng in i qua.
b. Vt c cc ht mang in t do.
c. Vt c cu trc mng tinh th
d. C a,b.
1.2 Th no l vt cch in?
a. Vt khng c ht mang in t do.
b. Vt khng cho dng in i qua.
c. Vt trng thi trung ho v in.
d. C ba yu t trn
1.3 1. Cc yu t no nh hng n tnh dn in ca vt
-
26
cht?
a. Cu to c. in trng ngoi
b. Nhit d. C ba yu t trn
1.4 2. Da vo tnh cht cu to cho bit cht no c kh
nng dn in tt nht?
a. Nhm c. Bc Vng
b. ng d. St
1.5 3. Da vo tnh cht cu to cho bit cht no c kh
nng cch in tt nht?
a. Khng kh. c. Gm.
b. Thu tinh. d. Mi ca
1.6 4. Cc ht no l ht mang in?
a. ion+ I c. on--
b. e-- d. C ba ht nu trn
1.7 5. Dng in trong cht in phn l dng ca loi ht
mng in no?
a. e-- c. ion-
ion+
d.
Gm b v c.
1.8 Dng in trong cht kh l dng ca cc ht mang in
no?
a. e-- c. ion -
b. ion+
d. C a,b,c.
1.9 Dng in trong kim loi l dng ca ht mang in no?
a. e- c. ion-
b. ion+
d. Gm a,b,c
1.10 Trong cht bn dn dng in di chuyn l dng ca ht
mang in no?
a. e-- c. on--
b. ion+ d. l trng
-
27
HOT NG II: T NGHIN CU TI LIU
Hc vin tham kho cc ti liu di y :
Nguyn Tn Phc Linh kin in t, NXB Tng hp TP. HCM, 2003
Nguyn Minh Gip Sch tra cu linh kin in t SMD. NXB Khoa hc v K
thut, H Ni, 2003
Nguyn Kim Giao,
L Xun Th
K thut in t 1. NXB Gio dc, H Ni, 2003
Gio trinh linh kin in t, D n GDKT v DN (VTEP), H
Ni, 2007
VT L LP 11, NXB Gio dc, H Ni.
xun Th K thut in t, NXB Gio dc, H Ni, 2005.
Ni dung cn nghin cu:
- Cc vt liu in: Cch in, Dn in, Bn dn..
- Cc yu t nh hng n c tnh dn in ca vt liu.
- Dng in trong cc mi trng v ng dng trong k thut in, in t.
HOT NG III: HC TI XNG TRNG
1.Ni dung:
- Phn bit cht dn in cch in, dn in.
- Nghin cu cc c tnh ca vt liu trong cc iu kin khc nhau.
a. Hnh thc t chc: T chc theo nhm nh t 2 - 4 hc sinh di s hng dn
tp trung ca gio vin.
b. Dng c:
c. My o VOM.
d. B ngun bin i c cc mc in p khc nhau t 0-1000v
e. B dng c cm tay ngh in t.
f. Cc vt liu dn in v cch in khc nhau.
a. Qui trnh thc hin:
-
28
A. Phn bit cht cch in v dn in: Pht cc vt liu khc nhau hin c trong
xng cho hc sinh.
g. Cho bit cht no dn in, cht no cch in bng cm nhn khch quan, trnh
by l do.
h. Dng my o VOM xc nh cht cch in, dn in trong iu kin bnh
thng.
B. Nghin cu c tnh dn in v cch in trong cc iu kin khc nhau:
Trnh by cch mc mch o dng (nh hnh v), mc vt liu cn nghin cu ni
tip trn mch. t ln mch cc in p khc nhau nu xut hin dng in qua mch c
ngha vt dn in, Nu khng xut hin dng in c ngha vt khng dn in.
Vt liu cn nghin cu
in tr hn dng
my o VOM ch o dng
Ngun cung cp c cc gi tr thay i khc nhau
+V
-
29
BI 2
LINH KIN TH NG
M BI: CIE 01 09 02
Gii thiu:
Cc mch in t c to nn t s kt ni cc linh kin in t vi nhau bao gm
hai loi linh kin chnh l linh kin th ng v linh kin tch cc trong phn ln l cc
linh kin th ng. Do mun phn tch nguyn l hot ng, thit k mch, kim tra
trong sa cha cn phi hiu r cu to, nguyn l hot ng ca cc linh kin in t,
trong trc ht l cc linh kin in t th ng.
Mc tiu thc hin:
Hc xong bi hc ny, hc vin c nng lc:
Phn bit in tr, t in, cun cm vi cc linh kin khc theo cc c tnh ca
linh kin.
c ng tr s in tr, t in, cun cm theo qui c quc t.
o kim tra cht lng in tr, t in, cun cm theo gi tr ca linh kin.
Thay th / thay tng ng in tr, t in, cun cm theo yu cu k thut ca
mch in.
Ni dung:
in tr
T in.
Cun cm.
HOT NG I: HC L THUYT TRN LP C THO LUN
2.1. IN TR
in tr l mt trong nhng linh kin in t dng trong cc mch in t t cc
gi tr dng in v in p theo yu cu ca mch. Chng c tc dng nh nhau trong c
-
30
mch in mt chiu ln xoay chiu v ch lm vic ca in tr khng b nh hng
bi tn s ca ngun xoay chiu.
2.1.1. Cu to cc loi in tr
Tu theo kt cu ca in tr m ngi ta phn loi:
- in tr hp cht cacbon:
in tr c cu to bng bt cacbon tn trn vi cht cch in v keo kt dnh ri
p li, ni thnh tng thi hai u c dy dn ra hn. Loi in tr ny r tin, d lm
nhng c nhc im l khng n nh, chnh xc thp, mc tp m cao. Mt u
trn thn in tr c nhng vch mu hoc c chm mu. l nhng quy nh mu
dng biu th tr s in tr v cp chnh xc.
Cc loi in tr hp cht bt than ny c tr s t 10 n hng chc mgm, cng
sut t 1/4 W ti vi W.
- in tr mng cacbon:
Cc in tr c cu to mng cacbon c gii thiu trn Hnh 2.1. Cc in tr
mng cacbon thay th hu ht cc in tr hp cht cacbon trong cc mch in t.
ng l lp y cc hp cht cacbon, in tr mng cacbon gm mt lp chun xc mng
cacbon bao quanh mt ng ph gm mng. dy ca lp mng bao ny to nn tr s
in tr, mng cng dy, tr s in tr cng nh v ngc li. Cc dy dn kim loi c
kt ni vi cc np c hai u in tr. Ton b in tr c bao bng mt lp keo
pxi, hoc bng mt lp gm. Cc in tr mng cacbon c chnh xc cao hn cc
in tr hp cht cacbon, v lp mng c lng mt lp cacbon chnh xc trong qu
trnh sn xut. Loi in tr ny c dng ph bin trong cc my tng m, thu thanh, tr
s t 1 ti vi chc mgm, cng sut tiu tn t 1/8 W ti hng chc W; c tnh n
nh cao, tp m nh, nhng c nhc im l d v.
Dy dn
Lp ph pxi
Lp in tr
Li gm
Np kim loi
Hnh 2.1: Mt ct ca in tr mng cacbon
-
31
- in tr dy qun:
in tr ny gm mt ng hnh tr bng gm cch in, trn qun dy kim loi
c in tr sut cao, h s nhit nh nh constantan mangani. Dy in tr c th trng
men, hoc khng trng men v c th qun cc vng st nhau hoc qun theo nhng rnh
trn thn ng. Ngoi cng c th phun mt lp men bng v hai u c dy ra hn.
Cng c th trn lp men ph ngoi c cha ra mt khong c th chuyn dch mt
con chy trn thn in tr iu chnh tr s.
Do in tr dy qun gm nhiu vng dy nn c mt tr s in cm. gim thiu
in cm ny, ngi ta thng qun cc vng dy trn mt l cch in dt hoc qun hai
dy chp mt u cho hai vng dy lin st nhau c dng in chy ngc chiu nhau.
Loi in tr dy qun c u im l bn, chnh xc, chu nhit cao do c cng
sut tiu tn ln v c mc tp m nh. Tuy nhin, in tr loi ny c gi thnh cao.
- in tr mng kim loi:
in tr mng kim loi c ch to theo cch kt lng mng niken-crm trn thn
gm cht lng cao, c x rnh hnh xon c, hai u c lp dy ni v thn c ph
mt lp sn. in tr mng kim loi n nh hn in tr than nhng gi thnh t gp
khong 4 ln. Cng sut danh nh khong 1/10W tr ln. Phn nhiu ngi ta dng loi
in tr mng kim loi vi cng sut danh nh 1/2W tr ln, dung sai 1% v in p
cc i 200 V.
- in tr xt kim loi:
in tr xt kim loi c ch to bng cch kt lng mng xt thic trn thanh
thu tinh c bit. Loi in tr ny c m rt cao, khng b h hng do qu nng v
cng khng b nh hng do m t. Cng sut danh nh thng l 1/2W vi dung sai
2%.
RR
Hnh 2.2. K hiu in tr trn s mch
Ngoi cch phn loi nh trn, trong thit k, tu theo cch k hiu, kch thc ca
in tr, ngi ta cn phn loi theo cp chnh xc nh: in tr thng, in tr chnh
xc; hoc theo cng sut: cng sut nh, cng sut ln.
2.1.2. Cch mc in tr :
-
32
Trong mch in tu theo nhu cu thit k m ngi ta s dng in tr c gi tr
khc nhau, tuy nhin trong sn xut ngi ta khng th ch to mi gi tr ca in tr
c m ch sn xut mt s in tr tiu biu c trng theo cc s nh sau:
BNG 2.1: CC GI TR THNG DNG TRONG SN XUT
(theo cc n v m, fara...)
1 2,
2
3,
3
4,
7
5,
6
6,
8
8,
2
1
,2
2,
7
3,
9
1
,5
1
,8
Nn trong s dng nh thit k phi s dng mt trong hai phng n sau:
Mt l phi tnh ton mch in sao cho ph hp vi cc in tr c sn trn th
trng.
Hai l tnh ton mc cc in tr sao cho ph hp vi mch in.
in tr mc ni tip: Cch ny dng tng tr s ca in tr trn mch in
(Hnh 2.5).
R1 R2 Rn
Hnh 2.5:Mch in tr mc ni tip
Theo cng thc:
Rt = R1 + R2 + .. + Rn (2.1)
Rtd: in tr tng ng ca mch in
V d: Cho mch in nh hnh v. Vi R1 = 2,2K, R2 = 4,7K. Tnh in tr
tng ng ca mch in
R2R1
Gii: T cng thc (2.1) ta c Rt = 2,2 + 4,7 = 6,9K
-
33
Trong thc t, ngi ta ch mc ni tip t 02 n 03 in tr trnh rm r cho
mch in.
in tr mc song song: Cch ny dng gim tr s in tr trn mch in.
Trong thc t tnh ton cn ghi nh l in tr tng ng ca mch in lun nh hn
hoc bng in tr nh nht trn mch in, iu ny rt thng sy ra sai st khi thay th
tng ng trong khi thc hin sa cha. Ngoi ra, d dng trong tnh ton, thng
thng ngi ta dng in tr cng tr s mc song song, khc vi mc ni tip, mch
mc in tr song song c th mc nhiu in tr song song t tr s theo yu cu,
ng thi t c dng chu ti ln theo mn v tng vng din tch to nhit trn
mch in khi cng sut ta nhit cao(Hnh 2.6).
R1
R2
Rn
Hnh2.6:Mch in tr mc song song
Theo cng thc: Rtd
1
1
1
R+
2
1
R +...+
Rn
1
Rtd: in th tng ng ca mch in
V d: Cho mch in nh hnh v. Vi R1 = 5,6K, R2 = 4,7K. Tnh in tr tng
ng ca mch in.
R1
R2
Gii: T cng thc ta c
Rtd = 21
2.1
RR
RR
=
7,46,5
7,4.6,5
= 2,55K
2.1.3. Cc thng s k thut c bn ca in tr:
- Cng sut in tr l tch s gia dng in i qua in tr v in p t ln hai
u in tr. Trong thc t, cng sut c qui nh bng kch thc in tr vi cc in
tr mng dng trn, ghi trn thn in tr vi cc loi in tr ln dng dy qun v bng
s, tra trong bng vi cc loi in tr hn b mt (SMD).
-
34
- Sai s ca in tr l khong tr s thay i cho php ln nht trn in tr. Sai s
nm trong phm vi t 1% n 20% tu theo nh sn xut v c ghi bng vng mu, k
t, hoc bng tra.
- Tr s in tr l gi tr ca in tr c ghi trn thn bng cch ghi trc tip, ghi
bng vng mu, bng k t.
2.1.4. Bin tr:
Bin tr dng thay i gi tr ca in tr, qua thay i c s cn tr in
trn mch in. Hnh 2.3 minh ho bin tr.
in p vo
in p raVR
Chnh thay i
Hnh 2.3: Cu trc ca bin tr
K hiu ca bin tr:
o K hiu ca bin tr trn s nguyn l c minh ho trn Hnh 2.4.
K hiu bin tr thng thng
,
2
1
Loi tinh chnh thay i rng
32
VR
3,
2
VR
3
VR
11--
VR1...................................
VR2 22
31
Loi hai bin tr chnh ng b (ng trc)
31
-
35
................................
3
................
1
Loi bin tr c cng tc
2
Hnh 2.4: K hiu cc loi bin tr
Phn loi:
o Bin tr than: Mt bin tr c ph lp bt than, con chy v chn ca bin tr l
kim loi d hn. Loi bin tr ny dng trong cc mch c cng sut nh dng qua
bin tr t vi mA n vi chc mA phn cc cho cc mch in l ch yu.
o Bin tr dy qun: Mt bin tr c qun dy in tr, con chy v chn ca bin
tr l kim loi. Loi bin tr ny dng gim p hoc hn dng trong cc mch in c
cng sut ln dng qua mch t vi chc n vi trm mA. Trong k thut in i khi
dng rt ln c th n vi A thng gp trong cc mch kch t cc ng c in. Khi s
dng hay thit k mch dng loi in tr ny cn ch n kh nng to nhit ca in
tr sao cho ph hp.
Ngoi cch chia thng thng trn trong k thut ngi ta cn cn c vo tnh cht
ca bin tr m c th chia thnh bin tr tuyn tnh, bin tr logarit. Hay da vo cng
sut m phn loi thnh bin tr gim p hay bin tr phn cc. Trong thc t cn ch
n cc cch chia khc nhau trnh lng tng trong thc t khi gi tn trn th trng.
2.2 T in:
T in c nhiu loi v nhiu c khc nhau. Phm vi tr s in dung c t 1,8pF
n trn 10.000F.
V cu to, t in c chia thnh hai loi chnh:
- Loi khng phn cc.
- Loi phn cc.
i vi dng in mt chiu, t in l linh kin c tc dng ngn dng in i qua,
mc d c th c mt dng np khi mi kt ni t in vi ngun mt chiu v sau li
ngng ngay khi t in va mi c np y. Vi trng hp dng in xoay chiu,
dng in ny tc ng ln t in vi hai na chu k ngc nhau lm cho t in c tc
dng dn dng in i qua, nh th khng c cht in mi.
2.2.1. Cu to v k hiu quy c ca mt s t in thng dng
- T in giy: gm c 2 l kim loi t xen gia l bn giy dng lm cht cch
in v cun trn li. hai u l kim loi cun trn c dy dn ni ra hn. T ny
-
36
c th c v bc bng kim loi hay ng thu tinh v hai u c bt kn bng cht keo
plastic. T giy c u im l kch thc nh, in dung ln. Nhc im ca t l r
in ln, d b chp.
- T in mica: gm nhng l kim loi t xen k nhau v dng mica lm cht in
mi, ngn cch cc l kim loi. Cc l kim loi l ni vi nhau v ni vo mt u ra, cc
l kim loi chn ni vi nhau v ni vo mt u ra. T mica c bao bng v plastic.
T mica c tnh nng tt hn t giy nhng gi thnh t hn.
- T in gm: t in gm dng gm lm in mi. T gm c kch thc nh
nhng tr s in dung ln.
- T in du: t dng du lm in mi, c tr s ln v chu c in p cao.
- T ho: t dng mt dung dch ho hc l axit boric lm in mi. Cht in mi
ny c t gia 2 l bng nhm lm hai cc ca t. Khi c mt in p mt chiu t
gia 2 l th to ra mt lp oxyt nhm mng lm cht in mi, thng lp ny rt mng,
nn in dung ca t kh ln. T ho thng c dng hnh ng, v nhm ngoi l cc m,
li gia l cc dng, gia 2 cc l dung dch ho hc. T c bc kn trnh cho
dung dch ho hc khi b bay hi nhanh, v dung dch b kh s lm cho tr s ca t
gim i. T ho c u im l tr s in dung ln v c gi thnh h, nhng li c nhc
im l d b r in. Khi dng t ho cn kt ni ng cc tnh ca t vi ngun cung
cp in. Khng dng c t ho cho mch ch c in p xoay chiu tc l c cc tnh
bin i.
Phin t
Vt liu in mi pxi
Phin t
Dy dn
Nhn pha bn
Phin t
Nhn t trn xung
Hnh 2.7: Mt ct ca t in kiu bn cc
-
37
Hinh 2.8: Cu to ca t gm, t mng kim loi v t Tantalum
- T bin i: gm cc l nhm hoc ng xp xen k vi nhau, mt s l thay i v
tr c. Tm tnh (m c nh) khng gn vi trc xoay. Tm ng gn vi trc xoay v
tu theo gc xoay m phn din tch i ng gia hai l nhiu hay t. Phn din tch i
ng ln th in dung ca t ln, ngc li, phn din tch i ng nh th tr s in dung
ca t nh. Khng kh gia hai l nhm c dng lm cht in mi. T loi bin i
cn c gi l t khng kh hay t xoay. T bin i thng gm nhiu l ng ni song
song vi nhau, t xen k gia nhng l tnh cng ni song song vi nhau. Nhng l tnh
c cch in vi thn t, cn l ng c gn vo trc xoay v tip xc vi thn t.
Khi trc t c xoay th tr s in dung ca t cng c thay i theo. Ngi ta b tr
hnh dng nhng l ca t t c s thay i in dung ca t theo yu cu. Khi vn
t xoay cho l ng hon ton nm trong khe cc l tnh, nhm c c din tch i
ng l ln nht, th t c in dung ln nht. Khi vn t xoay sao cho l ng hon ton
nm ngoi khe cc l tnh, nhm c din tch i ng xp x bng khng, th lc , t
in c in dung nh nht, gi l in dung st. T xoay thng dng trong my thu
thanh hoc my to dao ng t c tn s cng hng.
- T tinh chnh hay l t bn chun: thng dng chnh in dung ca t in,
nhm t c tn s cng hng ca mch. Nhng t ny thng c tr s nh v phm
vi bin i hp. Ngi ta ch tc ng ti t tinh chnh khi ly chun, sau th c nh v
tr ca t.
-
38
- T in in phn: c nhng c tnh khc vi t khng phn cc. T c cu to
ban u gm c hai in cc c phn cch bng mt mng mng ca cht in phn,
giai on cui cng, ngi ta dng mt in p t ln cc in cc c tc dng to ra
mt mng oxyt kim loi rt mng khng dn in. Dung lng ca t tng ln khi lp
in mi cng mng, nh vy c th ch to t in c in dung ln vi kch thc nh.
Do t in in phn c ch to c cc tnh, tng ng vi cc tnh ban u khi hnh
thnh lp in mi, cc tnh ny c nh du trn thn ca t. Nu ni ngc cc tnh
c th lm ph hu lp in mi, do , t s b hng. Mt hn ch khc ca t in in
phn l lng in phn cn li sau lc hnh thnh ban u s c tc dng dn in v lm
cho t b r in.
Cht liu chnh dng cho t in in phn l nhm v cht in mi l bt dung
dch in phn. T in in phn c dng hnh ng t trong v nhm. Nhng t in
phn loi mi c kh nng t c tr s in dung ln vi kch thc nh. Phm vi tr
s in dung t 0,1 F n 47 F vi c rt nh v t 1 F n 4700 F, thm ch ln
hn. in p mt chiu lm vic ca t in in phn thng thp t 10V n 250V
hoc 500V, mi t in in phn u c dung sai ln v t khi chn tr s ti hn.
- T in plistiren: t c ch to t l kim loi xen vi lp in mi l mng
mng plistiren, thng plistiren bao bc to thnh lp cch in. Loi t in ny c
tn tht thp tn s cao (in cm thp v in tr ni tip thp), n nh v tin
cy cao. Phm vi gi tr t 10pF n 100000pF vi dung sai khong 1%. Trng hp t
c dng ng vi chiu di xp x 10mm x 3,5 mm ng knh, thng cho tr s in
dung ln hn. Loi t in ny c dng cho cc mch iu chnh, mch lc, mch tn
s FM v cc mch iu khin khc c yu cu chnh xc, tin cy v n nh cao
v tn tht thp.
- T polycacbonat: loi t ny c ch to di dng tm hnh ch nht c th
cm vo bng mch in. Chng c tr s in dung ln ti 1 F vi kch thc rt nh, tn
hao thp v in cm nh. T in polycacbonat thng c thit k c bit v dng
cho mch in vi kch thc xp x 7,5 mm x 2,5 mm khong cch chn l 7,5 mm.
K hiu ca cc loi t in trn s nguyn l c gii thiu trn Hnh 2.17.
+
-
39
Hnh 2.9: Gii thiu k hiu cc dng t in thng dng
T nhm(dng trc)
T nhm(dng trn)
T Tantal(dng trn)
T hnb mt
T myla(dng trn)
T gmn khi(dng trc)
T gmn khi(DIP)
T agm
Hnh 2.10 : Cc dng t in thng dng
2.2.2.Cch mc t in: Trong thc t cch mc t in thng t khi c s dng,
do cng dng ca chng trn mch in thng thng dng lc hoc lin lc tn hiu
nn sai s cho php ln. Do ngi ta c th ly gn ng m khng nh hng g n
mch in. Trong cc trng hp i hi chnh xc cao nh cc mch dao ng, cc
mch iu chnh...ngi ta mi s dng cch mc theo yu cu cho chnh xc.
Mch mc ni tip: (Hnh:2.11)
CnC2C1
Hnh 2.11: Mch t in mc ni tip
Cng thc tnh: Ctd
1=
1
1
C+
2
1
C+...+
Cn
1
Ctd: in dung tng ng ca mch in
Cng ging nh in tr gi tr ca t in c sn xut theo bng 2.1. Trong mch
mc song song in dung tng ng ca mch in lun nh hn hoc bng in dung
nh nht mc trn mch
V d: Cho t hai t in mc ni tip vi C1= 1mF, C2= 2,2mF tnh in tr tng
ng ca mch in.
Gii: T cng thc tnh ta c: Ctd = 21
21
CC
CC
=
2,21
2,21
= 0,6875mF
Mch mc song song: (Hnh 2.12)
-
40
C1
C2
Cn
Hnh 2.12: Mch t in mc song song
Cng thc tnh: Ctd = C1+ C2 +...+ Cn
Ctd: in dung tng ng ca mch in.
V d: Tnh in dung tng ng ca hai t in mc ni tip, Vi C1= 3,3mf;
C2=4,7mF.
Gii: T cng thc ta c: Ctd = C1+ C2 = 3,3 + 4,7 = 8mF
2.2.3. Cc thng s k thut c bn ca t in
- chnh xc: Tu theo cp chnh xc m tr s t in c cp sai s nh trnh by
trong Bng 2.2:
BNG 2.2: CC CP SAI S CA T IN
CP SAI
S
SAI S CHO
PHP
Cp .001 0,1%
Cp .002 0,2%
Cp .005 0,5%
Cp .01 1%
Cp 0 2%
Cp I 5%
Cp II 10%
Cp III 20%
Cp IV - 20% n +
30%
Cp V - 20% n +
50%
Cp VIII - 40% n +
100%
-
41
- in p lm vic l in p t ln t trong thi gian lm vic di m t
khng b nh thng (Khong 10 000 gi).
Trn thc t gi tr ghi trn thn l in p lm vic, tuy nhin vi cc t hin
nay trn th tr-ng do Vit Nam v Trung Quc sn xut th-ng ghi l in p
nh thng nn trong thay th cn ch n khi thay th t mi trong sa cha
cn chn ln hn m bo an ton.
- in p nh thng l in p m qu in p th cht in mi ca t
b nh thng.
- Tr s danh nh ca t in tnh bng Fara hoc cc -c s ca Fara l
1F (10-6 Fara), nF (10-9 Fara) v pF(10-12 Fara) c ghi trn t in bng m quy c.
2.3. Cun cm:
Cun cm gm nhng vng dy cun trn mt li cch in. C khi qun cun cm
bng dy cng v t vng, lc cun cm khng cn li. Ty theo tn s s dng m
cun cm gm nhiu vng dy hay t, c li hay khng c li.
Cun cm c tc dng ngn cn dng in xoay chiu trn mch in, i vi dng
in mt chiu cun cm ng vai tr nh mt dy dn in.
2.3.1. Cu to ca cun cm:
Theo cu to, cun cm gm c cc loi:
Cun cm khng c li l cun cm c qun trn mt ng cch in, c t s
vng dy thch ng vi tn s cao.
Cun cm c qun trn li bng s, cng dng cho tn s cao, loi ny dng s
l cht in mi tt, tiu hao t nn c h s phm cht cao.
Cun cm c qun nhiu vng, nhiu lp, dng cho tn s thp hn.
tng tr s in cm ngi ta thng qun nhiu vng dy trn li c t
thm ln.
2.3.2. K hiu ca cun cm
Trong mch in cun cm c k hiu nh Hnh 2.20
L1
Hnh 2.13: Cc k hiu ca cun cm
-
42
Ngoi cch k hiu nh trn cun cm c th c k t nh T hay L
Hnh 2.14: Hnh dng cc loi cun cm
Trong k thut cun cm c qun theo yu cu k thut t hng hay t qun theo
tnh ton nn cun cm khng c mc ni tip hay song song nh in tr hoc t in
v phi tnh n chiu mc cc cun cm vi nhau ng thi gy cng knh v mt cu
trc mch in. Tr cc mch lc c tn s cao hoc siu cao trong cc thit b thu pht
v tuyn.
2.4. CCH C TR S LINH KIN TH NG:
Cc linh kin th ng c kch thc ln thng d phn bit, d ghi tr s nhng
vi cc linh kin c kch thc nh th hnh dng i khi gn ging nhau, ch khc nhau
v mu sc nn trong thc t i khi d b nhm ln. Sau y l cch ghi tr s ca cc
linh kin th ng.
2.4.1. Ghi trc tip: L ghi trc tip cc thng s k thut trn thn linh kin. Thng
thng ch thc hin c vi cc linh kin c kch thc ln.i vi linh kin loi ny
ch vic c tr s bnh thng.
V d:
in tr: Hnh 2.15
-
43
470uF - 25v85 0C
T in: Hnh 2.16
Cun cm: Hnh 2.17
Cuon day loi khong kh
Cuon day loi thep khung ch nhatCuon day loi Ferit tru
Cuon day loi Ferit vong xuyen
2.4.2.Ghi bng vng mu: Cch ny thng dng ghi trn thn cc linh kin c
kch thc nh. Cch ghi thng dng nht l dng 04 vng mu nh hnh v. Hnh 2.18
Hnh 2.18: Cch k hiu in tr bng cc vng c mu khc nhau
BNG 2.3: BNG QUI C MU LINH KIN TH NG
Qui c mu i thnh s S lng s 0 Sai s
en 0 Khng c 20%
Vng ch s
Vng ch s lng s 0
Vng ch sai s
-
44
Nu 1 0 Mt s 0 1%
2 00 Hai s 0 2%
Cam 3 000 Ba s 0 3%
Vng 4 0.000 Bn s 0 4%
Lc (xanh l) 5 00.000 Nm s 0 5%
Lam (xanh dng) 6 000.000 Su s 0 6%
Tm 7 0.000.000 By s 0 7%
Xm 8 00.000.000 Tm s 0 8%
Trng 9 000.000.000 Chn s 0 9%
Vng kim 0,... 0,1 5%
Bc kim 0,0... 0,01 10%
V d: c in tr c vng mu nh sau
- Nu; ; en; vng kim = 1;2; khng c s 0, sai s 5%. c l:12;5%
- Cam; cam; ; bch kim = 3; 3; hai s 0; sai s 10%. c l: 3300;10%
c t in c vng mu nh sau:
- Vng; Tm; Nu; vng kim = 4; 7; mt s 0; sai s 5%. c l: 470pf
- ; ; ; vng kim = 2;2; hai s0; sai s 5% c l: 2200pf.
c cun dy c vng mu nh sau:
- Nu; Lc; cam; vng kim = 1; 5; ba s 0; sai s 5%. c l: 15000H.
- Lam; Xm; ; Vng kim = 6; 8; Hai s0; sai s 5%. c l: 6800H.
Ch : Vi c loi linh kin 04 vng mu ch c ba loi sai s 5% vng kim; 10% bc
kim; 20% en hoc khng c vng mu. Cc linh kin c 5 hoc 6 vng mu l loi linh
kin chnh sc mi s dng loi sai s khc, c s dng ch yu trong cc mch c
chnh sc cao nh thit b o lng. Hnh 2.19
Linh kin k hiu bng 05 vng mu
Vng ch s
Vng ch s lng s 0
Vng ch sai s
Vng ch u
Vng ch s
Vng ch s lng s 0
Vng ch sai s
-
45
Linh kin k hiu bng 06 vng mu
Hnh 2.19: Cc linh kin ghi nhiu vng mu
2.4.3. Ghi bng k t: Loi linh kin c ghi gi tr bng k t thng c kch
thc rt nh c dng ch yu trong cng ngh hn b mt SMD: Surface Mount
Device. Ngoi nhim v ghi tr s linh kin i khi do nhu cu k t cn c th dng
ghi m s linh kin do mun tra cu thng s k thut ca linh kin ngi ta cn phi
tra bng tuy nhin vic dng bng tra trong thc t ch tin hnh vi cc linh kin bn dn
hoc cc linh kin th ng dng tch hp(nhiu lnh kin t chung vi nhau).
Gn ging nh loi linh kin ghi bng mu linh kin ghi bng k t c ghi bng s
hoc ch. V d hnh 2.20
Hnh 2.20: Cch k hiu bng k t thng thng.
- Nu l in tr th c nh sau: 12000
- Nu l t in thi c nh sau: 12000pf
- Nu l cun cm th c nh sau: 12000H
Trn thc t t in v cun dy thng c tr s nh. Vi t thng di 1000pf,
Vi cun dy thng vi chc H.
Vi cc gi tr nh hn10 ngi ta thng chn thm ch R trong k hiu. V d
Hnh 2.21
1 2 3
ch s S lng s 0
1 R 2
-
46
in tr c c l: 1,2 v 0,47
Hnh 2.21: Cch k hiu linh kin gi tr nh hn 10
CU HI V BI TP
Cu hi nhiu la chn:
Hy la chn phng n ng tr li cc cu hi di y bng cch t en
vo vung thch hp:
TT Ni dung cu hi a b c d
2.1 in tr c tnh cht g?
a. Dn in DC
b. Dn in AC
c. Dn in DC v AC.
d. Khng cho dng in i qua.
2.2 Trong mch in, in tr lm nhim v g?
a. Gim p.
b. Hn dng.
c. Phn cc.
d. C ba y t trn.
2.3 Cn c vo u phn loi in tr?
a. Cu to.
b. tnh cht.
c. Cng dng.
d. Cp chnh sc.
2.4 in tr mc ni tp c tnh cht g?
a. Tng gi tr
b. Gim gi tr
c. Gi tr khng thay i.
d. C ba u sai
2.5 in tr mc song song c tnh cht g?
a. Tng gi tr
b. Gim gi tr
R47
-
47
c. Tng cng sut
d. C ba u ng
2.6 Thng thng ngi ta mc in tr song song lm
g?
a. Tng cng sut chu ti
b. Gim gi tr in tr trn mch
c. Tng din tch to nhit trn mch
d. C ba iu trn
2.7 in tr c thng s k thut c bn no?
a. Tr s
b. Sai s
c. Cng sut
d. C ba iu trn
2.8 Bin tr trong mch in dng lm g?
a. Thay i gi tr ca in tr.
b. Thay i in p phn cc
c. Thay i dng phn cc
d. C ba u sai
2.9 Trong k thut bin tr than dng lm g?
a. Hn ch dng in qua mch
b. Gim in p cung cp cho mch
c. Phn cc cho mch in
d. C ba iu trn.
2.10 Trong k thut bin tr dy qun dn lm g?
a. Hn ch dng qua mch in.
b. Gim in p cung cp cho mch in
c. Phn cc cho mch in
d. Gm a,b
2.11 T in c tnh cht g?
a. Ngn dng mt chiu
b. Ngn dng xoay chiu
c. C a,b ng
d. C a,b sai
2.12 Trong k thut t in c chia lm my loi?
-
48
a. Phn cc
b. Khng phn cc
c. Thng
d. Gm a, b.
2.13 T mc ni tip c tnh cht g?
a. Tng tr s
b. Gim tr s
c. Khng thay i
d. Tt c u sai
2.14 T mc song song c tnh cht g?
a. Tng tr s
b. Gim tr s
c. Khng thay i
d. Tt c u sai.
2.15 Trong thc t thng thng ngi ta mc t theo cch
no?
a. Mc ni tip
b. Mc song song
c. Mc hn hp
d. Tt c cc cch trn
2.16 T in c nhng thng s c bn no?
a. Tr s
b. in p lm vic
c. Cp chnh xc
d. Tt c cc yu t trn.
2.17 Cun cm c tnh cht g?
a. Ngn dng DC
b. Ngn dng AC
c. C a, b ng
d. C a, b sai
2.18 H s t cm ca cun cm ph thuc vo yu t no?
a. S vng dy.
b. Phm cht li
c. K thut qun.
-
49
d. C ba iu trn.
2.19 C my hnh thc ghi tr s linh kn th ng?
a. Ghi trc tip.
b. Ghi bng vng mu.
c. Ghi bng k t.
d. C ba cch trn.
2.20 Cch ghi tr s linh kin th ng da vo u?
a. Gi tr ca linh kin.
b. Kch thc ca linh kin.
c. Hnh dng ca linh kin
d. Cu to ca linh kin.
HOT NG II: T NGHIN CU TI LIU:
Ti liu:
Nguyn Tn Phc Linh kin in t, NXB Tng hp TP. HCM, 2003
Nguyn Minh Gip SCH TRA CU LINH KIN IN T SMD. NXB Khoa
hc v K thut, H Ni, 2003
Nguyn Kim Giao,
L Xun Th
K thut in t 1. NXB Gio dc, H Ni, 2003
Gio trinh linh kin in t, D n GDKT v DN (VTEP), H
Ni, 2007
S tay tra cu linh kin in t,
xun Th K thut in t, NXB Gio dc, H Ni, 2005.
Ni dung cn nghin cu:
- Cu to, tnh cht, k hiu, ng dng cc linh kin in t .
-
50
HOT NG III: THC HNH TI XNG TRNG
1. Ni dung:
- Phn bit cc linh kin th ng ri v trong mch in.
- o kim tra nh gi cht lng linh kin.
2. Hnh thc t chc: T chc theo nhm nh mi nhm t 2 -4 hc sinh.
Gio vin hng dn ban u hc sinh thc hin cc ni dung di s theo di, ch
dn ca gio vin.
3. Dng c:
- Cc linh kin th ng ri
- Cc mch in t thc t
- My o VOM s hoc kim.
- My o t .
- My o cun cm.
4. Qui trnh thc hin:
- Pht linh kin v mch in cho hc sinh quan st t khng nh vai tr ca
linh kin th ng trong mch in.
- Hng dn hc snh cc c im phn bit cc loi linh kin vi nhau.
- Hng dn hc sinh c tr s cc loi linh kin.
- Hng dn hc sinh o kim tra tr s ca linh kin.
- Hng dn hc sinh nh gi cht lng linh kin
Kt lun cc trng thi h hng ca linh kin.
BI 3
-
51
LINH KIN BN DN
M BI: CIE 01 09 03
GII THIU
Trong mch in t nu ch thun cc linh kin th ng th khng th hot ng
c, do cc thng tin khng c to ra hoc khng c bin i v khng c x l
(iu ch, khuch i, chuyn i sang cc dng tn hiu khc..). Linh kin tch cc trong
mch gi vai tr quan trng khng th thiu c, l iu kin to ra cc thng tin tn
hiu, bin i v x l thng tin, l nn tng cu to nn thit b in t. Ngy nay, vi s
pht trin khng ngng ca khoa hc, cng ngh, nht l cng ngh bn dn, trong cc
thit b in t, chng ta gp ch yu l linh kin bn dn.
MC TIU THC HIN
Hc xong bi hc ny, hc vin c nng lc:
- Phn bit cc linh kin bn dn c cng sut nh theo cc c tnh ca linh kin.
- Phn bit c cc loi linh kin bng my o VOM theo c tnh ca linh kin.
- Xc nh c tnh k thut ca linh kin theo ni dung bi hc bng cch s dng
bng tra cu.
- Kim tra nh gi cht lng linh kin bng VOM trn c s c tnh ca linh
kin.
NI DUNG
- Khi nim cht bn dn
- Tip gip PN - it tip mt.
- Phn loai v ng dng it.
- Tranzito BJT.
- Tranzito trng.
- Diac, SCR, Triac
-
52
HOT NG I: NGHE THUYT TRNH TRN LP C THO LUN
3.1. KHI NIM
3.1.1. Khi nim: t lu, tu theo tnh cht ca vt cht, ngi ta thng chia vt
cht lm hai loi l cht dn in v cht cch in. T u th k trc ngi ta ch
n cht bn dn in (gi tt l cht bn dn).
nh ngha: cht bn dn l cht c c tnh dn in trung gian gia cht dn
in v cht cch in.
S phn chia trn ch c tnh cht tng i, v in tr sut ca cht bn dn cn
ph thuc vo nhiu yu t khc, nu ch da vo in tr sut nh ngha th cha th
biu th y cc tnh cht ca cc cht bn dn.
Cc tnh cht ca cht bn dn:
in tr ca cht bn dn gim khi nhit tng, in tr tng khi nhit gim.
Mt cch l tng khng tuyt i (- 2730C) th cc cht bn dn u tr thnh cch
in. in tr ca cht bn dn thay i rt nhiu theo tinh khit. Cc cht bn dn
hon ton tinh khit c th coi nh cch in khi nhit thp. Nhng nu ch c mt
cht tp cht th dn in tng ln rt nhiu, thm ch c th dn in tt nh cc cht
dn in.
in tr ca cht bn dn thay i di tc dng ca nh sng. Cng nh sng
cng ln th in tr ca cht bn dn thay i cng ln .
Khi cho kim loi tip xc vi bn dn hay ghp hai loi bn dn N v P vi nhau
th n ch dn in tt theo mt chiu. Ngoi ra, cc cht bn dn c nhiu c tnh khc
na.
3.1.2. S dn in trong cht bn dn tinh khit.
Ngi ta nghin cu v a ra kt lun: dng in trong cc cht dn in l do
cc in t t do chy theo mt chiu nht nh m sinh ra. Cn dng in trong cht bn
dn khng nhng do s di chuyn c hng ca cc in tch m (in t), m cn l s
di chuyn c hng ca cc in tch dng (l trng).
V d: Mt nguyn t gcmani c bn in t ngoi cng. N lin kt vi bn
nguyn t chung quanh. To thnh 08 in t lp ngoi cng. Mi lin kt ny kh bn
vng. Cho nn nhit rt s khng c tha in t t do, do khng c kh nng dn
in. Gi l trng thi trung ho v in.
-
53
Khi nhit tc ng vo cht bn dn tng ln, th in t lp ngoi cng c
cung cp nhiu nng lng nht. Mt s in t no c nng lng thng c s
rng buc ca ht nhn th ri b nguyn t ca n, tr thnh in t t do, di chuyn
trong mng tinh th. Ch ca chng chim trc y tr thnh l trng v tr thnh ion
dng. Ion dng c nhu cu ly mt in t bn cnh tr v trng thi trung ho v
in. Ngi ta coi ion dng c mt l trng, khin cho mt in t bn cnh d nhy
vo lp i. Ch ca in t ny li b trng, ngha l li to nn mt l trng khc v li
c mt in t cnh nhy vo lp ch trng. C nh vy, mi khi c mt in t t
do thot khi rng buc vi ht nhn ca n, chy lung tung trong mng tinh th, th cng
c mt l chy trong . Thc cht, s di chuyn ca l trng l do di chuyn ca cc
in t chy ti lp l trng.
Trong cht bn dn tinh khit bao gi s in t v s l trng di chuyn cng bng
nhau. nhit thp th ch c t cp in t l trng di chuyn. Nhng nhit cng
cao th cng c nhiu cp in t, l trng di chuyn. S di chuyn ny khng c chiu
nht nh nn khng to nn dng in. Nu by gi u thanh bn dn vi hai cc
dng, m ca mt pin, th gia hai u thanh bn dn c mt in trng theo chiu t
A n B (hnh 3.12.). Cc in t s di chuyn ngc chiu in trng, cc in t ti
lp l trng cng chy ngc chiu in trng. Dng in t v dng l trng hp thnh
dng in trong thanh bn dn. nhit cng tng th dng in cng ln.
B
0--->
0--->
dng l trng0--->
dng in t
0---> 0--->
0--->
0--->0--->
o--->0--->0--->
0--->
0---> 0--->
0--->
0--->
_
0--->
0--->
0--->
E
0--->
------------->
+
E
0--->
A
------------->
0--->
0--->
Hnh 3.1: Chiu chuyn ng ca cc in t v l trng
3.1.3 S dn in trong cht bn dn tp:
Bn dn N:
Bn dn loi N cn gi l bn dn in t hay bn dn m. Nu cho mt t tp cht
asen (As) vo tinh th gecmani (Ge) tinh khit ta thy hin tng sau: nguyn t asen c
-
54
nm in t lp ngoi cng, nn ch c 4 in t ca asen kt hp vi bn in t lin
kt gia asen v bn nguyn t gecmani, cn in t th nm th tha ra. N khng b
rng buc vi mt nguyn t gecmani no, nn tr thnh in t t do chy lung tung
trong tinh th cht bn dn. Do , kh nng dn in ca loi bn dn ny tng ln rt
nhiu so vi cht bn dn thun. Nng tp cht asen cng cao th s in t tha cng
nhiu v cht bn dn cng dn in tt. Hin tng dn in nh trn gi l dn in
bng in t. Cht bn dn gi l cht bn dn N,
Nu cho tp cht ho tr 5 nh pht pho (P), asen (As), antimoan (Sb) vo cc cht
ho tr 4 nh gecmani (Ge), silic (Si), cacbon (C) ta c bn dn N. Trong cht bn dn
loi N th cc in t tha l cc ht in tch m chim a s. S lng in t tha ph
thuc nng tp cht. Cn s cc cp in t - l trng do ph v lin kt to thnh th
ph thuc vo nhit .
Nu u hai cc ca b pin vo hai u mt thanh bn dn loi N, th di tc ng
ca in trng E, cc in t tha v cc cp in t - l trng ang di chuyn ln xn
s phi di chuyn theo hng nht nh: in t chy ngc chiu in trng cn cc l
trng chy cng chiu in trng. Nh trong mch c dng in. Dng in do cc
in t tha sinh ra ln hn nhiu so vi dng in do cc cp in t - l trng to nn .
V th cc in t tha ny gi l in tch a s.
Bn dn P:
Bn dn loi P cn gi l bn dn l trng hay bn dn dng. Nu cho mt t
nguyn t Ini (In) vo trong tinh th gecmani tinh khit th ta thy hin tng sau:
nguyn t indi c ba in t lp ngoi cng, nn ba in t ch lin kt vi ba in t
ca ba nguyn t gecmani chung quanh. Cn lin kt th t ca ini vi mt nguyn t
gecmani na th li thiu mt mt in t, ch thiu gi l l trng, do c l trng
nn c s di chuyn in t ca nguyn t gcmani bn cnh ti lp l trng v li to
nn mt l trng khc, khin cho mt in t khc li ti lp. Do cht bn dn loi P
c kh nng dn in. L trng coi nh mt in tch dng. Nguyn t ini trc kia
trung tnh, nay tr thnh ion m, v c thm in t.
Hin tng dn in nh trn gi l dn in bng l trng. Cht bn dn l bn
dn loi P hay cn gi l bn dn dng.
Nu c tp cht ho tr ba nh ini (In), bo (B), gali (Ga) vo cc cht bn dn ho
tr bn nh Ge, Si, C th c bn dn loi P.
-
55
Trong cht bn dn loi P, l trng l nhng ht mang in tch chim a s. S
lng l trng ph thuc vo nng tp cht, cn s cc cp in t - l trng do ph v
lin kt to thnh th ph thuc vo nhit .
Nu u hai cc ca b pin vo hai u mt thanh bn dn loi P th di tc ng
ca in trng E, cc l trng (a s) v cc cp in t - l trng ang di chuyn lung
tung theo mi hng s phi di chuyn theo hng quy nh. Nh trong mch c dng
in. Dng in do l trng sinh ra ln hn nhiu so vi dng in do cp in t - l
trng. V th trong bn dn loi P cc l trng l in tch a s.
3.1.4. u nhc im ca linh kin bn dn:
u im:
- Linh kin bn dn khng c si nung, nn khng cn ngun si nung, va khng
tn in va trnh c nhiu tp do si nung gy ra.
- Linh kin bn dn c th tch nh gn, d lp rp.
- Linh kin bn dn c tui th tng i di.
Nhc im:
- Linh kin bn dn c in p ngc nh hn so vi n in t chn khng,
- Linh kin bn dn c dng in ngc (Dng r),
- Linh kin bn dn c in tr ngc khng ln, li khng ng u,
- Cc thng s k thut ca linh kin bn dn thay i theo nhit .
3.2 TIP GIP PN - IT TIP MT
3.2.1.Tip gip PN:
Cu to: (Hnh 3.2)
Hnh:3.2: Cu to mi ni PN
Khi ghp hai loi bn dn P v N vi nhau th in t tha ca N chy sang P v cc
l trng ca bn dn P chy sang N. Chng gp nhau vng tip gip, ti hp vi nhau
v tr nn trung ho v in.
Bn
dnP
Bn dnN
-
56
vng tip gip v pha bn dn P, do mt l trng nn ch cn li nhng ion m.
V vy, vng c in tch m. vng tip gip v pha bn dn N, do mt in t
tha, nn ch cn li nhng ion dng. V v vng c in tch dng, do , hnh
thnh in dung mt tip gip. n y, s khuch tn qua li gia P v N dng li.
Vng tip gip tr thnh mt bc ro ngn khng cho l trng t P chy qua N v in
t N chy qua P. Ring cc ht mang in tch thiu s l cc in t trong bn dn P v
cc l trng trong bn dn N l c th vt qua tip gip, v chng khng b nh hng
ca bc x hng ro ngn, m ch ph thuc nhit . Trong bn dn P, cc in tch a
s l cc l trng, cn trong bn dn N l cc in t tha.
Nguyn l hot ng:
+ Phn cc thun c trnh by trn Hnh 3.3
Hnh 3.3: Phn cc thun cho mi ni PN
Do tc dng ca in trng E, cc in t tha trong N chy ngc chiu in
trng vt qua tip gip sang P, ti hp vi cc l trng trong P chy v pha tip
gip. in t t do t m ngun s chy v bn dn N thay th, to nn dng thun c
chiu ngc li. Dng thun tng theo in p phn cc. Ngoi ra, phi k n s tham
gia vo dng thun ca cc in t trong cp in t - l trng. Khi nhit tng ln th
thnh phn ny tng, lm cho dng thun tng ln.
+ Phn cc ngc c trnh by trn Hnh 3.4
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57
Hnh 3.4: Phn cc ngc cho mi ni PN
Do tc ng ca in trng E cc in t tha trong N v cc l trng trong P u
di chuyn v hai u m khng vt qua c tip gip, nn khng to nn c dng
in. Ch cn mt s in tch thiu s l nhng l trng trong vng bn dn N v cc
in t trong vng bn dn P (ca cp in t - l trng) mi c kh nng vt qua tip
gip. Chng ti hp vi nhau. Do c mt dng in t rt nh t cc m ngun chy
ti thay th cc in t trong P chy v pha N v to nn dng in ngc rt nh theo
chiu ngc li. Gi l dng ngc v n chy t bn dn m (N) sang bn dn dng (P).
Dng ngc ny ph thuc vo nhit v hu nh khng ph thuc in p phn cc.
n khi in p phn cc ngc tng qu ln th tip gip b nh thng v dng ngc
tng vt ln.
3.2.2 it tip mt:
it tip mt gm hai bn dn loi P v loi N tip gip nhau. u bn dn P l cc
dng, u bn dn N l cc m. it tip mt c nhiu c to nh, hnh thc khc nhau.
Do din tip xc ln, nn dng in cho php i qua c th ln hng trm miliampe n
hng chc ampe, in p ngc c th t hng trm n hng ngn vn. Nhng in dung
gia cc cc ln ti hng chc picfara tr ln, nn ch dng c tn s thp nn
in.
K hiu ca it tip mt :
DIODE
Nguyn l lm vic ca it tip mt
Khi ghp hai loi bn dn P v N vi nhau th in t tha ca N chy sang P v cc
l trng ca bn dn P chy sang N. Chng gp nhau vng tip gip, ti hp vi nhau
v tr nn trung ho v in.
vng tip gip v pha bn dn P, do mt l trng nn ch cn li nhng ion m.
V vy, vng c in tch m. vng tip gip v pha bn dn N, do mt in t
-
58
tha, nn ch cn li nhng ion dng. V v vng c in tch dng, do , hnh
thnh in dung mt tip gip. n y, s khuch tn qua li gia P v N dng li.
Vng tip gip tr thnh mt bc ro ngn khng cho l trng t P chy qua N v in
t N chy qua P. Ring cc ht mang in tch thiu s l cc in t trong bn dn P v
cc l trng trong bn dn N l c th vt qua tip gip, v chng khng b nh hng
ca bc x hng ro ngn, m ch ph thuc nhit . Trong bn dn P, cc in tch a
s l cc l trng, cn trong bn dn N l cc in t tha.
By gi ta xt s vn chuyn ng ca cc phn t mang in khi phn cc cho
it.
+ Phn cc thun c trnh by trn Hnh 3.5
Hnh 3.5: Phn cc thun cho it tip mt
Do tc dng ca in trng E, cc in t tha trong N chy ngc chiu in
trng vt qua tip gip sang P, ti hp vi cc l trng trong P chy v pha tip
gip. in t t do t m ngun s chy v bn dn N thay th, to nn dng thun c
chiu ngc li. Dng thun tng theo in p phn cc. Ngoi ra, phi k n s tham
gia vo dng thun ca cc in t trong cp in t - l trng. Khi nhit tng ln th
thnh phn ny tng, lm cho dng thun tng ln.
+ Phn cc ngc c trnh by trn Hnh 3.6
-
59
Hnh 3.6: Phn cc ngc cho it tip mt
Do tc ng ca in trng E cc in t tha trong N v cc l trng trong P u
di chuyn v hai u m khng vt qua c tip gip, nn khng to nn c dng
in. Ch cn mt s in tch thiu s l nhng l trng trong vng bn dn N v cc
in t trong vng bn dn P (ca cp in t - l trng) mi c kh nng vt qua tip
gip. Chng ti hp vi nhau. Do c mt dng in t rt nh t cc m ngun chy
ti thay th cc in t trong P chy v pha N v to nn dng in ngc rt nh theo
chiu ngc li. Gi l dng ngc v n chy t bn dn m (N) sang bn dn dng (P).
Dng ngc ny ph thuc vo nhit v hu nh khng ph thuc in p phn cc.
n khi in p phn cc ngc tng qu ln th tip gip b nh thng v dng ngc
tng vt ln.
3.3. PHN LOI V CC NG DNG C BN CA IT
3.3.1. it nn in: Do c tnh lm vic dng ln, p cao nn it nn in
c dng l it tip mt nh trnh by phn trn.
Cc mch nn din c bn:
- Mch nn in bn k: (Hnh 3.7)
Vdc OutVac In
T D
+
C
DIODE
Hnh 3.7: Mch nn in mt bn k
Nhim v cc linh kin trong mch nh sau:
T: Bin p dng tng hoc gim p (Thng thng l gim p)
D: it nn in.
C: T lc xoay chiu.
Nguyn l hot ng ca mch nh sau:
in p xoay chiu ng vo Vac in qua bin p c tng hoc gim p. c a
n it nn in. bn k dng it dn in np in cho t C. bn k m it b
phn cc ngc nn khng dn in. Nn ng ra ca mch nn Vdc out ta c in p
mt chiu.
- Mch nn in ton k dng hai it: (Hnh 3.8)
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60
T
Vac InVdc Out
D2
D1
DIODE
+
C
DIODE
Hnh 3.8: Mch nn in ton k dng hai it
Nhim v cc linh kin nh sau:
T: Bin p dng bin i in p xoay chiu ng vo
D1; D2: Nn dng in xoay chiu AC thnh dng mt chiu DC
C: T lc xoay chiu sau nn.
Nguyn l hot ng nh sau:
in p xoay chiu ng vo qua bin p bin i thch ng vi mch in. Khi u
trn ca bin p bn k dng it D1 dn in th u di ca bin p bn k m
nn it D2 khng dn in. Dng in nn qua D1 np in cho t lc C. Khi u trn
ca bin p l bn k m it D1 khng dn in th u di ca bin p l bn k dng
nn it D2 dn in np in cho t C. Nh vy dng in ng ra c lin tc c hai bn
k ca dng in xoay chiu nn c gi l mch nn in hai bn k. c im ca
mch l phi dng bin p m cun s cp c im gia nn khng thun tin cho mch
nu khng dng bin p, hoc bin p khng c im gia. khc phc nhc im
ny, thng thng trong thc t ngi ta dng mch nn in ton k dng s cu.
- Mch nn in ton k dng s cu: (Hnh 3.9)
T
Vac In
Vdc Out
D1D2
D3D4
DIODE
DIODE
DIODE
+
C
DIODE
Hnh 3.9: Mch nn in ton k dng s cu
Nhim v cc linh kin trong mch:
T: Bin p i in.
D1;D2;D3;D4: it nn in.
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61
C: T lc xoay chiu sau nn.
Nguyn l hot ng nh sau:
Dng xoay chiu ng vo qua bin p T, ng ra trn cun s cp c a n b
nn cu. Khi u trn ca bin p l bn k dng th u di ca bin p l bn k m.
Lc ny D1; D3 dn in np in cho t C. Khi u trn ca bin p l bn k m th u
di ca bin p l bn k dng. Lc ny D2; D4 dn in dn in np cho t C cng
chiu np ban u hnh thnh in p mt chiu ng ra.
Mch nn in tng i: (Hnh 3.10) Mch ny dng to ra in p mt chiu c
gi tr cao gp hai ln in p xoay chiu ng vo.
Mch nn in tng i mt bn k: (Hnh 3.10 a)
Vo ACVi AC
D1
+ C2
+C1 D2
Hnh 3.10 a: Mch nn in tng i mt bn k.
Trong nhim v cc linh kin nh sau:
D1; D2: Nn in bi p
C1; C2: T bi p.
Hot ng ca mch nh sau: bn k dng t C1 dn in qua it D2 np in
cho t C2. bn k m D1 dn in np in cho t C1. n bn k k tip Pha dng ca
in p xoay chiu np chng ln t C1 c dn qua it D2 np in cho t C2 Lc ny
in p DC ng ra l hai ln in p nh ca in p xoay chiu.
Mch in ny c nhc im l dng in nh, hiu sut khng cao, nn t c s
dng trong thc t.
Mch nn in tng i hai bn k: (Hnh 3.10 b)
Vac in
D2
D1
Vdc out
+
C2DIODE
DIODE
+
C1
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62
Hnh 3.10 b: Mch nn in tng i hai bn k.
Trong nhim v cc linh kin trong mch nh sau:
D1; D2: Nn in bi p
C1; C2: T bi p.
Hot ng ca mch nh sau: u trn ca ng vo l bn k dng it D1 dn
in np cho t C1 v ngun. Khi u trn i chiu l bn k m it D2 dn in np
in cho t C2 v ngun. Do hai t C1; C2 mc ni tip nn in p DC ng ra l tng in
p np trn hai t C1; C2 nn in p c tng i.
3.3.2. it tch sng: Cn c gi l it tip im.
- Cu to: hnh 3.11
Ka tt
KloiNAnt
Hnh 3.11: Cu to ca it tch sng
Gm mi nhn kim loi l cc dng, t ln mt mt ming bn dn loi N l cc
m.
- K hiu: ging nh it tip mt
DIODE
Hnh 3.12: K hiu ca it tch sng
-Tnh cht:: Tng t nh it tip mt nhng it tip im c th tch nh, cng
sut nh, in dung gia hai cc nh, nn dng tn s cao. Vng tip xc ca it tip
im nh, nn dng in cho php qua it thng khng qu 10 15mA v in p
ngc khng qu vi chc volt
-ng dng: Thng dng tch sng tn hiu trong cc thit b thu v tuyn, thit
b c chc nng bin i thng tin ....
3.3.3. it zne:
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63
- Cu to: it zne c cu to ging nh cc loi it khc nhng cc cht bn dn
c pha t l tp cht cao hn c dng in r ln. Thng thng hin nay trong k
thut ngi ta xn sut ch yu l it Silic.
- K hiu:
Dz
Hnh 3.13: K hiu ca it zne
- Tnh cht::
Trng thi phn cc thun it zne c c tnh ging nh it nn in thng
thng.
Trng thi phn cc ngc do pha tp cht vi t l cao nn dng r ln v in p
ngc thp, in p gi l in p zne Vz. Khi phn cc ngc n tr s Vz th dng
qua it tng m in p khng tng.
- ng dng: Li dng tnh cht ca it zne m ngi ta c th gi in p ti mt
im no khng i gi l ghim p hoc n p (Hnh 3.12).
Vd
D
R
VoVi
Hnh 3.14: Mch in s dng it zne
Vi: L in p ng vo
Vo L in p ng ra.
. Nu in p ng vo l tn hiu c bin cao hn in p Vz th ng ra tn hiu b
xn mt phn nh ch cn li khong bin bng Vz
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64
. Nu in p ng vo l in p DC cao hn Vz th ng ra in p DC ch bng Vz.
. Nu in p ng vo cao hn rt nhiu Vz. Dng qua it zne tng cao n mt
gi tr no vt qua gi tr cho php th it b nh thng. Lm cho in p ng ra b
trit tiu. Tnh cht ny c dng trong cc b ngun bo v chng qu p ngun
m bo an ton cho mch in khi ngun tng cao.
R trong mch gi vai tr l in tr hn dng hay gim p.
3.3.4. it quang (Photodiode):
- Cu to: it quang c cu to gn ging nh it tch sng nhng v bc cch
in thng c lm bng lp nha hay thu tinh trong sut d dng nhn nh sng
t bn ngoi chiu vo mi ni PN.
-K hiu:
Hnh 3.15: K hiu ca it quang
- Tnh cht:
Khi b che ti: in tr nghch v cng ln, in tr thun ln.
Khi b chiu sng: in tr nghch gim thp khong vi chc K. in tr thun
rt nh khong vi trm Ohm.
- ng dng: it quang c ng dng rng ri trong lnh vc iu khin t ng
mi nghnh c ng dng k thut in t. Nh my m tin, my m sn phm, Ca
m t ng, T ng bo chy ....v.v.
3.3.5. it pht quang: LED (Light Emitting Diode)
- Cu to: Li dng tnh cht bc x quang ca mt s cht bn dn khi c dng
in i qua c mu sc khc nhau. Li dng tnh cht ny m ngi ta ch to cc Led c
mu sc khc nhau.
- K hiu:
-
65
Hnh 3.16: K hiu ca LED
- Tnh cht:: Led c in p phn cc thun cao hn it nn in nhng in p
phn cc ngc cc i thng khng cao khong 1,4 - 2,8V. Dng in khong 5mA -
20mA.
- ng dng: Thng c dng trong cc mch bo hiu, ch th trng thi ca
mch. Nh bo ngun, ch bo m lng...
3.3.5. it bin dung (Varicap):
- Cu to: it bin dung l loi it c in dung thay i theo in p phn cc.
trng thi khng dn in, vng tip gip ca it tr thnh in mi cch in. in
dung Cd ca it ph thuc ch yu vo hng s in mi, din tch tip xc, chiu dy
ca in mi. Theo cng thc:
Cd = d
S
Cd: in dung ca it
: Hng s in mi
S: Din tch mi ni.
d: dy cht in mi.
-K hiu:
Hnh 3.17: K hiu ca it bin dung
-Tnh cht: Khi c phn cc thun th l trng v electron hai lp bn dn b
y li gn nhau lm thu hp b dy cch in d nn in dung Cd tng ln. Khi it c
phn cc ngc th l trng v electron b ko xa ra lm tng b dy cch in nn in
dung Cd b gim xung.
- ng dng: it bin dung c s dng nh nh mt t in bin i bng cch
thay i in p phn cc thay i tn s cng hng ca mch dao ng, cng hng
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66
nn c dng trong cc mch dao ng, cng hng c tn s bin i theo yu cu nh
b r i trong Radio, my thu hnh, my lin lc v tuyn, in thoi di ng ....
3.4. TRANZITO BJT:
3.4.1. Cu to:
Tranzito lng cc l linh kin c 3 chn, tranzito c s dng iu khin chuyn
mch hoc iu khin khuch i. Cc tranzito c loi c cu trc pnp, c loi c cu trc
npn (xem Bng tng quan). Tranzito lng cc loi npn dng mt dng nh i vo cc
bad B (cp dng) v mt in p dng (c quan h vi cc emit E) iu khin
dng ln hn chy t cc colect C n cc emit E. Ngc li, tranzito loi pnp dng
mt dng nh i ra khi cc bad B (rt dng) v mt in p m (c quan h vi cc
emit E) iu khin dng ln hn chy t cc emit n cc colect.
Tranzito lng cc l linh kin rt tin dng. Kh nng iu khin dng in ca
tranzito lng cc bng cch t tn hiu iu khin lm cho loi tranzito ny tr thnh
linh kin c ph dng trong cc mch chuyn mch iu khin bng in, mch iu
chnh dng, mch khuch i, mch dao ng v cc mch nh.
Di y l hnh nh n gin v cch lm vic ca tranzito lng cc loi npn (i
vi loi tranzito lng cc pnp, mi thnh t, cc phn cc v dng u o ngc li).
Mt tranzito lng cc npn c ch to bng cch ghp ming rt mng cht bn
dn loi p gia hai ming bn dn loi n. Khi khng c dng t vo cc bad B ca
tranzito, cc electron b ngn khng chy n cc colect v tip gip p. (Nh li l i
vi cc electron, chy qua tip gip pn cn mt nh thin cp cho cc electron mt
nng lng ln cc electron "thot" ra khi lc hp dn ca nguyn t v chy n
pha bn dn n). Ch rng nu in p m c t vo cc bad B, lc tip gip pn
gia cc bad v cc emit c thin p ngc. Do vng ngho c to nn v ngn
cn dng chy qua).
Nu mt in p dng (t nht bng 0,6V) c t vo cc bad B ca tranzito
npn, phn tip gip pn gia cc bad B v cc emit E c nh thin thun. Khi c
nh thin thun cc electron thot ra khi lc hp dn ca nguyn t v c thu ht v
cc dng bad. Mt s electron qua cc bad thot ra ngoi, nhng iu ny khng
mong mun.
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67
TNG QUAN V TRANZITO
LOI
TRANZI
TO
K HIU KIU HOT NG
LNG
CC
e
c
b NPN
Thng tranzito khng dn nhng vi mt dng nh i vo v
in p dng nh ti cc B lm cho cc E dn (cho php mt
lng dng ln chy t cc C n cc E). Tranzito hot ng
vi iu kin VC > VE. S dng trong cc ng dng chuyn
mch v khuch i.
e
c
b PNP
Thng tranzito khng dn, nhng vi mt dng nh i ra v
in p m nh ti cc B lm cho cc E dn (cho php mt
lng dng ln chy t cc E n cc C). Tranzito hot ng
vi VE > VC. S dng lm chuyn mch v khuch i.
JFET
S
D
G NJFET
Thng tranzito dn, nhng vi mt in p m nh ti cc
cng G lm cho cc ngun S ngng dn (khng cho dng t
cc ngun S chy n cc mng D). Tranzito hot ng vi
iu kin VD > VS. Khng i hi c dng cc cng G. S
dng lm chuyn mch v khuch i.
S
D
G PJFET
Thng tranzito dn, nhng vi mt in p dng nh ti cc
cng G lm cho cc ngun ngng dn (khng cho dng t cc
ngun S chy n cc mng D). Tranzito hot ng vi iu
kin VS > VD. Khng i hi c dng cc cng G. S dng
lm chuyn mch v khuch i.
MOSFET
LOI
NGHO
S
D
G2N3796
Thng tranzito MOSFET loi ngho dn, nhng vi in p
m nh t vo cng G lm cho cng ngun S ngng dn (lm
ngng dng ln chy qua cc mng D - cc ngun S). Tranzito
hot ng vi iu kin VD > VS. Khng i hi c dng cc
cng G. S dng trong cc ng dng chuyn mch v khuch
i.
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68
S
D
GPMOS
Thng tranzito MOSFET loi ngho dn, nhng vi in p
dng nh t vo cc cng G lm cho cng ngun S ngng
dn (lm ngng dng ln chy qua cc ngun S - cc mng
D). Tranzito hot ng vi iu kin VS > VD. Khng i hi
c dng cc cng. S dng lm chuyn mch v khuch i.
MOSFET
LOI
GIU
S
D
G2N3796
Thng tranzito MOSFET loi giu ngng dn, nhng vi
in p dng nh t vo cc cng G lm cho cng ngun S
dn (cho php dng ln chy qua cc mng D - cc ngun S).
Tranzito hot ng vi iu kin VD > VS. Khng i hi c
dng cc cng G. S dng lm chuyn mch v khuch i.
S
D
GIRF9510
Thng tranzito MOSFET loi giu ngng dn, nhng vi
in p m nh t vo cc cng G lm cho cng ngun S dn
(cho php dng ln chy qua cc ngun S - cc mng D).
Tranzito hot ng vi iu kin VS > VD. Khng i hi c
dng cc cng G. S dng lm chuyn mch v khuch i.
UJT E
B1
B2
UJT
Thng c dng rt nh chy t cc bad B2 n cc bad B1,
nhng mt in p dng t vo cc emit E lm cho cc
bad B1 hoc bad B2 tng dng chy. Tranzito hot ng vi
iu kin VB2 > VB1. Khng i hi c dng cc cng G. Ch
hot ng nh mt chuyn mch.
V bad loi p rt mng, nn cc electron o t ri khi emit v chy n colect.
Khi tng in p t vo bad lm tng hiu ng cc electron ri khi emit v do lm
tng lung electron chy t emit n colect. Cn nh rng dng theo qui c di chuyn
ngc vi lung electron. Nh vy, vi thut ng dng qui c mt in p dng v
dng i vo c t vo cc bad gy ra dng "dng" chy t colect n emit.
Tranzito ngng dn
V+ Vng ngho
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Hnh 3.18: M t trng thi ngng dn ca tranzito
Tranzito dn
Dng chy
V+ qui c Vng ngho
IB qui c
Hnh 3.19: M t trng thi dn ca tranzito
Hnh di y l ng cong c tuyn ca tranzito lng cc. ng c tuyn
ny m t mi tng quan ca dng cc bad IB v in p emit-colect VEC c dng
dn IE v IC.
+
Hnh 3.20: c tuyn vn - ampe ca tranzito lng cc
Cc thut ng m t hot ng ca tranzito l vng bo ho, vng ct, vng tch cc,
vng ngho v im ch Q (cha c tn hiu vo). Vng bo ho l vng hot ng ti
c dng colect cc i chy v tranzito hot ng ging nh chuyn mch kn mch t
colect n emit. Vng ct l vng hot ng gn vi trc honh ca th c tnh
colect, ti tranzito hot ng ging nh mt chuyn mch h mch - ch mt dng r
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70
rt nh chy trong kiu hot ng ny. Vng tch cc m t tranzito hot ng bn phi
vng bo ho v bn trn vng ct, ti mi quan h gn nh ng thng tn ti gia
cc dng cc cc (IB, IC, IE). nh thin thch hp vi cc in p DC v dng DC ca
tranzito thit lp im yu cu ca kiu hot ng tch cc, im ny c gi l im
ch hoc im Q.
3.4.2. Cc tnh cht c bn:
3.4.2.1. Cc qui tc quan trng:
Qui tc 1: i vi tranzito npn, in p ti colect VC phi ln hn in p ti
emit VE t nht l vi phn mi ca mt vn, nu khng th dng s khng chy qua
tip gip colect-emit. i vi tranzito pnp, in p emit phi ln hn in p colect
mt lng tng t.
Qui tc 2: i vi tranzito npn, c st p t bad n emit l 0,6 V. i vi
tranzito pnp, c in p 0,6 -V tng t bad n emit. V ngha hot ng, iu c
ngha l in p bad VB ca tranzito npn t nht phi ln hn in p VE l 0,6 V; nu
khng th tranzito s khng cho mt dng qua emit-colect. i vi tranzito pnp, VB t
nht phi nh hn in p VE l 0,6 V, nu khng th tranzito s khng cho mt dng
chy t colect n emit.
3.4.2.2. Cng thc:
Cng thc c bn m t quan h ca tranzito lng cc (t nht l trong vng tch
cc) l:
IC = hFE IB = IB
Trong , IB l dng bad, IC l dng colect, v hFE (cng cn gi l ) l li
dng. Mi tranzito c mt tr hFE ring. li hFE ca tranzito thng l tr khng i,
khong t 10 n 500, nhng c th thay i cht t theo nhit v thay i theo in p
colect-emit. ( li hFE ca tranzito c cho trong ti liu tra cu). Gii thch cng
thc trn ca tranzito mt cch n gin l nu c li hFE ca tranzito l 100 v mt
dng i vo bad (tranzito npn) hoc dng i ra khi bad (tranzito pnp) l 1 mA, lc
c dng colect l 100 mA. C gii hn cho dng chy qua tranzito cc cc ca tranzito
v gii hn mc in p t vo cc cc ca tranzito.
3.4.2.3. Cc loi tranzito
Tn hiu nh Loi tranzito ny thng c dng khuch i
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tn hiu nh nhng cng c th s dng lm
chuyn mch. Tr s li hFE t 10 n 500 vi
dng IC danh nh cc i vo khong t 80
n 600 mA. Tranzito ny c c hai loi npn v
pnp. Tn s hot ng cc i l vo khong t 1
n 300 MHz.
Chuyn mch nh
Cc tranzito ny ch yu dng lm chuyn mch
nhng cng c th dng lm khuch i. Tr s
li hFE t 10 n 200 vi dng IC danh nh cc
i vo khong t 10 n 100 mA. Tranzito ny c
c hai loi npn v pnp, tn s hot ng cc i l
vo khong t 1 n 300 MHz. Tc chuyn
mch cc i vo khong t 10 n 2000 MHz.
Tn s cao (RF)
Cc tranzito ny c dng cho tn hiu nh v
cng dng cho cc ng dng chuyn mch vi tn
s cao v tc chuyn mch ln. Vng cc bad
rt mng v kch thc ca tranzito rt nh. Cc
tranzito ny c th dng trong cc b khuch i
HF, VHF, UHF, CATV v MATV v trong cc
my to sng. Cc tranzito ny c c hai loi pnp
v npn v c tn s danh nh cc i vo khong
2000MHz v IC cc i t 10 n 600 mA.
Cng sut
Cc tranzito ny c dng trong cc b khuch
i cng sut ln v cc b cung cp cng sut.
Colect c kt ni vi phin kim loi to
nhit. Cng sut danh nh vo khong t 10 n
300 W vi tn s danh nh vo khong t 1 n
100 MHz. Tr s dng IC cc i t 1 n 100 A.
Cc tranzito ny c c hai loi pnp v npn v loi
Darlington (npn v pnp).
Cp Darlington
y l hai tranzito trong mt v. Cc tranzito ny
c n nh cao, ti mc dng ln. li hFE
ca tranzito ny ln hn li ca mt tranzito.
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72
Tranzito ny c c hai loi D-npn v D-pnp.
Tranzito quang
Tranzito ny hot ng nh mt tranzito lng
cc nhy sng (cc bad c l sng). Khi c
nh sng tip xc vi vng cc bad lm xut
hin dng bad. Ph thuc vo loi tranzito
quang, nh sng c th tc ng nh l tc nhn
nh thin (tranzito hai chn).
Dy tranzito
Loi bao gi ny c nhiu tranzito kt hp trong
mt v bc tch hp. V d, mt dy tranzito
y c ch to gm 3 tranzito npn v 2 tranzito
pnp.
3.5: TRANZITO HIU NG TRNG:
3.5.1. Khi qut v tranzito hiu ng trng
Tranzito hiu ng trng (JFET) l linh kin c 3 cc, c dng lm cc chuyn
mch iu khin bng in, iu khin khuch i v in tr iu khin in p. Khng
ging nh cc tranzito lng cc, JFET c bit c iu khin bng in p, chng
khng i hi c dng nh thin. Mt c im khc ca JFET l bnh thng JFET dn
khi khng c chnh lch in p gia cc cng G v cc ngun S. Tuy vy, nu c s
chnh lch in p gia cc cc ny, JFET s cn tr mnh dng chy (dng nh chy
qua cc cc mng cc ngun). Vi l do ny, cc JFET thng c gi l linh kin
ngho, khng ging nh cc tranzito lng cc l cc linh kin giu (tranzito lng cc
tr thnh in tr nh khi dng / p t vo cc cc bad).
JFET c cu dng knh n hoc knh p. Vi mt tranzito JFET knh n, mt in p
m t vo cc cng G (lin quan vi cc ngun S) lm gim dng chy t cc mng D
n cc ngun S (tranzito ny hot ng vi iu kin VC > VS). Vi mt tranzito knh
p, mt in p dng t vo cc cng G lm gim dng chy t cc ngun S n cc
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73
mng D (tranzito hot ng vi iu kin VS > VC). (xem k hiu trong bng tng quan
v tranzito).
JFET dn Cn tr ln
Dng qui c Vng ngho
Hnh 3.21: Cc trng thi JFET dn v JFET ngng dn
Mt c im quan trng ca JFET l s dng tr khng c bit ln ng vo (vo
khong 1010 ). Tr khng ng vo ln c ngha l JFET cho mt dng nh (nh hn
pico Ampe) hoc khng cho dng qua v do t nh hng hoc khng nh hng n
cc linh kin bn ngoi hoc khng nh hng n cc mch kt ni vi cng ca
tranzito, khng ly dng t mch iu khin v khng c dng khng mong mun i vo
mch iu khin. Kh nng ca mch JFET iu khin dng chy trong khi duy tr mt
tr khng ng vo c bit ln lm cho linh kin rt tin li trong vic s dng lm cc
mch chuyn mch analog hai hng, cc tng vo ca cc mch khuch i, ngun dng
hai cc n gin, cc mch khuch i, mch dao ng, chuyn mch logic in t iu
khin li, mch trn m...
Mt JFET knh n c lm bng cht bn dn silicon loi n c cha hai bu
silicon loi p t hai bn. Cc cng G c kt ni vi cc bu loi p, trong khi cc
mng v cc ngun c kt ni vi hai cc ca knh loi n (xem hnh v).
Khi khng c in p t vo cc cng G ca JFET knh n, dng chy t do qua
trung tm knh n, cc in t khng gp kh khn khi chy qua knh n, c mt t ht
mang in tch m ti v tr ny gip cho vic dn in. Tuy nhin, nu cng c xc
lp n in p m (lin quan n cc ngun), vng gia cc bu bn dn loi p v
trung tm knh n s to nn hai tip gip thin p ngc (mt tip gip lin quan n
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74
bu trn v mt tip gip lin quan n bu di). iu kin thin p ngc to nn
vng ngho c m rng. in p cng cng m th vng ngho cng rng v khi cc
electron kh c th i qua knh. i vi JFET knh p, ta o ngc cc tnh hung trn,
c ngha l thay th in p m cng bng mt in p dng, thay th knh n bng bn
dn knh p, thay th cc bu bn dn loi p bng cc bu bn dn loi n v thay th cc
ht mang in m bng cc ht (l) mang in dng.
vng Vng nh
in tr bo ho xuyn
Hnh 4.38: c tuyn vn - ampe ca JFET knh n
JFET knh p th ID - VDS ca JFET knh p
Hnh 3.22: c tuyn vn - ampe ca JFET knh p
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th JFET knh n Hnh 4.38 trn y m t c