GIÁO TRÌNH ĐIỆN TỬ CĂN BẢN

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TRNG AI HOC A LAT

KHOA CONG NGHE THONG TIN

Giao trnh

IEN TCAN BAN

Thang 1 - 2005


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LI NOI AU

Giao trnh IEN T CAN BAN la tai lieu hoc tap danh cho sinh vienKhoa Cong nghe Thong tin.

ien t can ban trnh bay cau tao va hoat ong cua cac linh kien ient va mach cua chung. ay la nhng kien thc c s e hieu biet cau truc maytnh va cac thiet b phan cng cua ky thuat cong nghe thong tin. Noi dung chuyeu cua giao trnh la mo ta cau tao, ac trng cua cac linh kien ien t bandan nh diode, transistor, IC va cac mach ng dung can ban cua chung.

Giao trnh gom 11 chng

Chng 1: Mot so khai niemChng 2: Diode ban dan va mach diodeChng 3: TransistorChng 4: Phan cc transistorChng 5: Khuyech ai transistorChng 6: Khuyech ai cong suatChng 7: Cac hieu ng tan so cua mach khuyech aiChng 8: Cac linh kien ban dan ac bietChng 9: Khuyech ai thuat toan

Chng 10: Cac mach dao ongChng 11: Nguon nuoiNoi dung cua giao trnh rat rong ma thi gian lai han che trong 60 tiet

do o mot so van e b bo qua. Sinh vien co the tham khao them textbookbang tieng Anh sau ay tai th vien Khoa Cong nghe Thong tin.

Electronic Principles Malvino, Mc Graw-Hill, 1999Sinh vien cung co the vao Website: www.alldatasheet.com e co them

cac thong tin chi tiet ve so lieu ky thuat cua cac linh kien.Do trnh o ngi viet co han, chac chan giao trnh con co nhieu thieu

sot. Rat mong c s gop y cua ban oc.

a Lat, thang 1 nam 2005Phan Van Ngha


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Chng IMOT SO KHAI NIEM

I.1 S GAN UNGTrong cuoc song chung ta thng xuyen dung s gan ung hay xap x.

Trong ky thuat cung vay. Chung ta thng dung cac mc gan ung sau: Gan ung ly tng (oi khi goi la gan ung bac 1) Gan ung bac 2 Gan ung bac 3 Mo ta chnh xac1) Gan ung ly tng. Mot oan day AWG22 dai 1 inch (2.54cm) co

ien tr thuan R=0.016, cuon cam L=0.24H va tu C=3.3pF. Neu chung tatnh ti tat ca cac anh hng cua RLC th tnh toan lien quan en dong va these mat nhieu thi gian va co the phc tap. V vay trong nhieu trng hp, en gian, co the bo qua RLC cua oan day dan.

S gan ung ly tng, la mach tng ng n gian nhat cua thiet b.V du, gan ung ly tng cua mot oan day noi la mot vat dan co tr khangZ=0. S gan ung nay la u cho cac thiet b ien t thong thng. Trng hpngoai le se xay ra tai tan so cao. Khi o phai xet en cam khang va dungkhang. Gia s rang 1 inch day noi co L=0.24H va C=3.3pF th tai tan so

f=10MHz cam khang va dung khang tng ng cua chung la 15.1 va4.82K. Chung ta thng dung gan ung ly tng oi vi day noi khi tan sof


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3) Gan ung bac 3 va cac gan ung cao hn. Gan ung bac 3 kemtheo mot so phan t na vao mach tng ng cua thiet b. Tham ch cac ganung cao hn na can phai lam khi phan tch mach. Tnh toan bang tay oivi cac mach tng ng gan ung cao hn bac 2 tr nen rat kho khan.Trong trng hp nay chung ta se dung chng trnh may tnh. V du EWB(Electronics Work Bench) hoac Pspice la cac phan mem may tnh trong odung cac gan ung bac cao e phan tch mach.

Tom lai, viec s dung gan ung loai nao la phu thuoc vao ye u cau congviec ma chung ta phai lam. Neu chung ta ang tm loi hay sa cha thiet b,gan ung bac 1 la u. Trong nhieu trng hp gan ung bac 2 la la chon totv de dung va khong yeu cau may tnh. oi vi cac gan ung cao hn can phaidung may tnh va mot chng trnh.

I.2 NGUON THE

Mot nguon the ly tng tao ra mot hieu ien the la hang so tren tai. Vdu n gian nhat cua mot nguon the ly tng la mot acqui hoan hao, mot acquima ien tr trong cua no bang 0.

Hnh 1-1a la hnh ve mot mach, trong o nguon the V1=10V noi viien tr tai RL=1. Von ke ch 10V, ung bang gia tr cua nguon the.

Hnh 1-1a: Nguon the va tai

Hnh 1-1b cho thay gian o cua hieu ien the tren tai va ien tr tai.

Theo gian o, hieu ien the tren tai van 10V khi ien tr tai thay oi t 1en 1M. Noi mot cach khac, mot nguon the ly tng tao ra mot the tren taila hang so bat chap ien tr tai la ln hay be. Vi mot nguon the ly tng, chco dong tai thay oi khi ien tr tai thay oi.


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Hnh 1-1b: Quan he gia the tai va tr tai

Gan ung bac 2 cua nguon the.Nguon the ly tng la thiet b ch co ve mat ly thuyet, no khong ton tai

trong thc te. V khi ien tr tai gan bang 0, dong tai se gan bang vo cung.Khong co mot nguon the thc nao co the tao ra mot dong tai vo han v nguonthe thc luon luon co ien tr trong (ien tr nguon). Gan ung bac 2 cua motnguon the phai kem theo ien tr trong nay.

Hnh 1-2a mo ta y tng nay. ien tr trong 1 noi tiep vi bo acqui lytng. Khi o gia tr ch tren Von ke la 5V thay v 10V.

Hnh 1-2a: Nguon the vi ien tr trong

Hnh 1-2b la gian o cua the tren tai va ien tr tai cua mot nguon thethc. The tren tai ch at c gia tr 10V khi ien tr tai ln hn ien trnguon nhieu lan, ln hn en mc co the bo qua ien tr nguon.

Nguon the manh (Stiff Voltage Source)Chung ta co the bo qua ien tr nguon khi no nho hn ien tr tai tnhat la 100 lan. Tat ca cac nguon the thoa man ieu kien nay goi la nguon themanh.


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Hnh 1-2b: The tren tai va tr tai oi vi nguon the thc

Mot nguon the manh neu thoa ieu kien:RS < 0.01RL (1-1)

ien tr tai be nhat ma nguon the van manh la:RL(min)=100RS (1-2)

Theo (1-2) ien tr tai be nhat phai bang 100 lan ien tr nguon. Trongtrng hp nay, sai so tnh toan do bo qua ien tr nguon la 1%. Gia tr sai sonay la u nho e bo qua trong gan ung bac 2.

Lu y: nh ngha ve nguon the manh ap dung cho ca nguon DC lan nguon AC. Gan ung bac 2 ch co y ngha tai tan so thap. Tai tan so cao, cac he so can

phai xem xet them la cam khang va dung khang.

I.3 NGUON DONG

Hnh 1-3: Nguon dong


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Mot nguon the DC cung cap mot the tren tai khong oi oi vi cac ien

tr tai khac nhau. Nguon dong DC tao ra mot dong tai la hang so oi vi cacien tr khac nhau. V du mot nguon dong ly tng la mot acqui co ien trtrong rat ln nh hnh 1-3.

Trong mach hnh 1-3, dong tai tnh bi:IL=V1/(Rs+RL)

vi RL=1, Rs =1M , dong tai bang:IL=10V/(1M+1)=10A

Trong tnh toan tren ay, ien tr tai anh hng khong ang ke len dong tai.

Hnh 1-4: anh hng cua ien tr tai oi vi dong tai

Hnh 1-4 ch ra anh hng cua ien tr tai oi vi dong tai. Dong tai

van la 10A trong mot vung rong cua ien tr tai. Khi ien tr tai ln hn10K (RL>1% RS) th dong tai bat au thay oi.Nguon dong manh.Chung ta co the bo qua anh hng cua ien tr nguon cua mot nguon

dong neu no ln hn ien tr tai t nhat la 100 lan. Moi nguon dong thoa ieukien nay goi la nguon dong manh.

Nguon dong manh neu thoa ieu kien:Rs >100RL (1-3)

Trong trng hp gii han, ien tr tai ln nhat ma nguon van c

xem la nguon dong manh khiRL(max)=0.01Rs (1-4)

Theo (1-4) ien tr tai ln nhat bang 1/100 ien tr nguon.Hnh 1-5a ky hieu mot nguon dong ly tng, trong o thiet b tao ra mot

dong hang Is vi ien tr noi cua nguon Rs la vo cung.Hnh 1-5b ch ra gan ung bac 2 cua nguon dong. o ien tr trong

RS mac song song vi nguon dong ly tng IS . Phan cuoi cua chng nay se


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xem xet nh ly Norton, khi o chung ta se biet tai sao Rs lai mac song songvi nguon dong IS.

Hnh 1-5: Nguon dong

Bang sau cho thay s khac nhau gia nguon dong va nguon the.

ai lng Nguon the Nguon dong

Rs Rat be Rat lnRL > 100 Rs < 0.01RsVL Hang Phu thuoc RLIL Phu thuoc RL Hang

I.4 NH LY THEVENIN

Hnh 1-6: The Thevenin


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nh ly la mot menh e co the chng minh bang toan hoc. Sau ay

chung ta xem xet mot so khai niem lien quan en nh ly Thevenin, ten motky s ngi Phap.

The Thevenin (VTH): Tren hnh 1-6, the Thevenin la the o c gia2 au ien tr tai (hai au AB) khi khong co ien tr tai (ien tr tai hmach). V vay oi khi the Thevenin con goi la the h mach.

The Thevenin:VTH =VOC (1-5)

Tr Thevenin (RTH): la ien tr o c gia 2 au ien tr tai khiien tr tai h mach va khi tat ca cac nguon giam ti 0.

Giam nguon ti 0 co y ngha khac nhau oi vi nguon dong va nguonthe. Cu the nh sau:

oi vi nguon the: ngan mach oi vi nguon dong: h mach

Vay nh ly Thevenin e cap en cai g? Theo nh ly Thevenin, moihop en cha mach gom nguon DC va cac ien tr tuyen tnh (la ien trkhong thay oi gia tr khi thay oi the tren no) nh hnh 1-6a co the thay thebang mot nguon the Thevenin va mot ien tr Thevenin tng ng nh hnh1-6b. Khi o dong qua tai bang

IL=VTH/(RTH+RL) (1-6)nh ly Thevenin la mot cong cu manh. No khong ch giup n gian cac

tnh toan ma con giup giai thch hoat ong cua cac mach ma neu ch dung cacphng trnh Kirchhoff th khong the lam c.

V du: Tnh the va tr Thevenin cho mach hnh 1-7.

Hnh 1-7

e tnh the Thevenin chung ta h mach ien tr tai RL. De dang thayrang VTH = 24V.

e tnh tr Thevenin can h mach tai va ngan mach nguon 72V. Khio:


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RTH = 4 + (3//6) = 6KCo the dung Von ke va Ohm ke e o the Thevenin va tr Thevenin.

o chnh xac cua cac phep o phu thuoc vao loai may o c s dung. V duneu s dung may o the loai ch th kim co o nhay 20K/V tai thang o 30Vth tr khang vao cua may o la 600K. Khi o the o c se be hn theThevenin mot chut. Thng ngi ta dung von ke co tr khang vao vao lnhn tr Thevenin t nhat la 100 lan. Khi o sai so se be hn 1%. e co trkhang vao cao, ngay nay ngi ta dung von ke so (Digital Multimeter) vi trkhang vao c 10M.

I.5 NH LY NORTON

Tren hnh 1-8a, dong Norton IN c nh ngha la dong tai khi ien trtai ngan mach. V vay dong Norton con goi la dong ngan mach.

IN = ISC (1-7)ien tr Norton la ien tr o gia hai au ien tr tai khi h mach

ien tr tai va tat ca cac nguon giam ti 0.RN = ROC (1-8)

Do ien tr Thevenin cung bang ROC, nen the viet:RTH=RN (1-9)

ngha la ien tr Thevenin va ien tr Norton la bang nhau.

Hnh 1-8: Mach Norton


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Trong hnh 1-8a, hop en cha mach bat ky gom nguon DC va cac ientr tuyen tnh. nh ly Norton phat bieu rang, co the thay the mach hnh 1-8abang mach hnh 1-8b.

Di dang bieu thc:

VL=IN(RN//RL) (1-10)

Theo (1-10) the tren tai bang dong Norton nhan vi ien tr tai macsong song vi ien tr Norton.

nh ly Norton va Thevenin la tng ng. Tren thc te, co the bienoi nguon the Thevenin thanh nguon dong Norton va ngc lai. Hnh 1-9 chothay cac cach bien oi.

Hnh 1-9: Bien oi Thevenin - Norton

Co the thay rang tr Norton va tr Thevenin la giong nhau. Quan he

gia dong Norton va the Thevenin laIN = VTH / RTH (1-11)

V du: Gia s rang chung ta a rut gon mot mach thanh mach Theveninnh hnh 1-10. Hay bien oi mach nay thanh mach Norton.

Li giai: Dung phng trnh (1-11) ta co:


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IN = 10V/2K = 5mAHnh 1-10b ve mach Norton tng ng cua mach Thevenin tren hnh

1-10a.

Hnh 1-10


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Chng IIDIODE BAN DAN VA MACH DIODE

II.1 CAC LOAI CHAT BAN DANTheo tnh chat dan ien, co 3 loai vat chat: Chat dan ien Chat khong dan ien (ien moi) Chat ban danTrong chat dan ien thng ch co 1 electron vung hoa tr, trong khi

o cac chat ien moi co 8 electron vung hoa tr. Ban dan co tnh chat trunggian gia ien moi va chat dan ien, chung co 4 electron vung hoa tr.

Germanium (Ge) va silicon (Si) la cac chat ban dan ien hnh. trang thai tinh the tinh khiet (khong b pha tap), moi nguyen t Ge va Si dung4 electron hoa tr cua chung e lien ket vi 4 electron hoa tr cua 4 nguyen tkhac tao ra cau truc tinh the ben vng ve mat hoa hoc.

Khai niem lo trong trong chat ban dan. nhiet o tren 0 o tuyetoi (>-2730C) cac electron trong mang tinh the se chuyen ong nhiet. Nhiet ocang cao th chuyen ong nhiet cua cac electron cang ln. Chuyen ong nhietnay co the lam cho 1 electron trong vung hoa tr chuyen len cac quy ao conang lng cao hn. Luc nay electron la t do. No di chuyen trong vung dan.

Cung vi s tao thanh mot electron t do, se xuat hien mot lo trong (mangien tch dng) trong vung hoa tr. So electron t do ung bang so lo trong.Lo trong la iem khac biet quan trong nhat gia ban dan va vat dan.

Neu ton tai 1 ien trng ngoai, th trong chat ban dan se co dong chayqua. Dong nay la dong cua cac electron t do va lo trong ngc chieu nhau.o dan ien cua ban dan tinh khiet tang theo nhiet o va co gia tr be.

e tang o dan ien cua ban dan tinh khiet can phai pha tap (doping).Co 2 cach thng dung:

Pha tap loai N (negative). e tang so electron t do trong ban dan,

ngi ta pha tap nguyen t hoa tr 5 (con goi la chat cho, Photpho chang han)vi ban dan tinh khiet, tao thanh ban dan loai N. Trong ban dan loai N, dedang thay rang nguyen t chat cho se tha 1 electron va lam cho so electrontrong ban dan loai N chiem a so. Lo trong la phan t thieu so trong ban danloai N.

Pha tap loai P (positive). Ngi ta pha tap nguyen t hoa tr 3 (con goila chat nhan, Nhom chang han) vao ban dan tinh khiet e tao ra chat ban dan


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loai P. Trong ban dan loai P, phan t tai ien a so la lo trong, phan t taiien thieu so la electron t do.

Ban dan loai N va loai P co the che tao t tinh the Ge hoac Si. Congnghe Ge la cong nghe cua nhng nam 60 (the ky 20). Ngay nay, hau het cacchat ban dan la Si.

II.2 TIEP XUC PN

Gia s co mot mau ban dan Si tinh khiet. Ngi ta pha tap mau ban dansao cho phia ben trai la ban dan loai P, con phia ben phai la ban dan loai N.Bien gii gia ban dan loai P va ban dan loai N goi la tiep xuc PN. Tiep xucPN a dan en cac phat minh ve diode, transistor, IC (Integrated Circuits)...Viec hieu biet tnh chat cua tiep xuc PN la c s e hieu biet hoat ong cuacac linh kien va thiet b ban dan.

Tiep xuc PN con goi la mot diode ban dan (t nay tr i goi la diode).Chung ta hay xem xet cac tnh chat cua mot diode khi khong phan cc.

Hnh 2-1: Tiep xuc PN khong phan cc

Tai lp tiep xuc, se hnh thanh mot vung ngheo ien tch (depletionlayer) do s khuyech tan cua electron t N vao P sau o cac electron nay taihp vi lo trong lam cho so phan t tai ien tai vung nay giam. S khuyechtan cung tao ra mot hang rao the nang hng t N sang P. nhiet o 250C,hang rao the nang co gia tr c 0.3V oi vi Ge va 0.7V oi vi Si. S hien

dien cua rao the ngan can qua trnh khuyech tan tiep tuc va he trang thaidng.


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II.3 DIODE BAN DAN CO PHAN CC

Hnh 2-2a cho thay ky hieu cua mot diode. Ben ban dan P goi la Anode(ky hieu la A), ben ban dan N goi la Cathode (ky hieu la K). Tren s o ngita ky hieu diode nh mot mui ten ch t P sang N hay t Anode sang Cathode.

Hnh 2-2b trnh bay mot mach diode. Trong mach nay diode c phancc thuan (Va>Vk). S phan cc thuan lam cho cac electron t do ben ban danN va lo trong ben ban dan P vt qua moi noi tao thanh dong ien trong diode(dong Iak).

Hnh 2-2: Diode va phan cc thuan diode

Trong phong th nghiem co the setup mot mach nh hnh 2-2b. Bangcach o dong va the tren diode ng vi phan cc thuan va phan cc nghch(Va


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Theo hnh 2-3, khi phan cc thuan, dong qua diode se khong ang kecho en khi Vak > hang rao the nang (barrier potential). Ngc lai, khi phancc ngc, co 1 dong ien rat be qua diode cho en ien ap at len diode vtqua ien the anh thung (Breakdown Voltage =BV).

Trong vung phan cc thuan, ien the tai o dong Iak bat au tangnhanh goi la ien the moi noi (knee voltage) cua diode. ien the moi noi cogia tr bang hang rao the nang. Khi phan tch mach diode phan cc thuanchung ta thng xet xem ien the tren diode la be hn hay ln hn ien themoi noi. Neu ln hn, diode de dang dan ien. Neu be hn, diode khong danien (dan ien kem). Chung ta nh ngha ien the moi noi cua diode siliconla:

Vk0.7V (2-1)ien the moi noi cua diode germanium la 0.3V. Hien nay diode

germanium t c dung, nhng ien the moi noi cua no thap la mot u iemva v vay mot so ng dung van dung diode germanium.

Khi ien the tren diode vt qua ien the moi noi th dong qua diodetang nhanh va theo quy luat tuyen tnh. Luc nay diode ong vai tro nh ientr. Chung ta goi ien tr nay la ien tr Bulk (RB) cua diode.

RB= RP+RN (2-2)Trong o RP va RN la ien tr tng ng cua vung P va vung N. Chung

phu thuoc vao mat o pha tap va kch thc cua cac vung nay. Thong thngRB < 1. Chung ta ch quan tam en RB cua diode trong gan ung bac 3.Trong giao trnh nay chung ta khong xem xet en gan ung bac 3.

Neu dong ien qua diode qua ln, s qua nhiet se pha huy diode. Vvay trong bang so lieu ky thuat (data sheet) cua nha may san xuat co ghi dongcc ai cua mot diode. o la dong ien toi a ma diode co the hoat ongbnh thng va khong lam giam tuoi tho cung nh cac ac trng cua no. Dongthuan toi a cua 1 diode thng c ghi bang Imax , IF(max), Io... V du diode1N456 co Imax =135mA.

Co the tnh cong suat tieu tan (power dissipation) cua mot diode giongnh tnh cong suat tieu tan cua mot ien tr. No bang tch gia dong va thetren diode.

PD = VD.ID (2-3)Gii han cong suat (power rating) cua mot diode la cong suat toi a ma

diode co the tieu tan va khong lam giam tuoi tho cung nh cac ac tnh khac.Neu ky hieu gii han cong suat la Pmax th

Pmax= Vmax.Imax (2-4)


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II.4 DIODE LY TNG

Hnh 2-4 cho thay gian o dong the cua mot diode trong vung phan ccthuan. Lu y rang dong qua diode xap x bang 0 cho en khi the tren diodeat ti gia tr hang rao the. Trong vung lan can 0.6V en 0.7V dong qua diodetang. Khi the tren diode ln hn 0.8V dong qua diode tang rat manh va o thla ng thang.

Hnh 2-4: Gian o dong the cua diode phan cc thuan

Tuy thuoc vao kch thc vat ly va mat o pha tap, cac ac trng cuadiode nh dong thuan toi a, gii han cong suat... co the co gia tr rat khacnhau. Mac du gia tr dong va the cua cac diode th khac nhau nhng dang cuagian o quan he gia dong va the tren moi diode tng t nhau nh hnh 2-4.Tat ca cac diode silicon eu co ien the moi noi xap x 0.7V.

Trong khi phan tch mach, hau nh chung ta khong can s chnh xactuyet oi. Do o co the dung gan ung cho diode. Chung ta hay bat au bang

gan ung ly tng. Theo o, diode nh mot thiet b co tnh chat sau: no danien tot (ien tr bang 0) khi phan cc thuan, va hoan toan khong dan ien(ien tr vo cung) khi phan cc ngc.

Hnh 2-5a ch ra gian o dong the cua 1 diode ly tng. Theo o diodely tng co ien tr bang 0 khi phan cc thuan va co ien tr bang vo cung khiphan cc ngc. Noi cach khac, diode ly tng giong nh mot cong tac


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(switch) nh hnh 2-5b. No ong (close) khi phan cc thuan va h (open) khiphan cc ngc.

Hnh 2-5: ng cong dong the cua diode ly tng va mo hnh

V du: Dung mo hnh diode ly tng tnh the tren tai va dong tai tren so hnh 2-6.

Hnh 2-6: Mach diode ly tng

Do diode phan cc thuan, no nh cong tac ang ong. Do o toan bonguon the 10V at len tr tai. Vay

VL=10VTheo nh luat Ohm, dong tai bang:IL=10V/1K = 10mA


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II.5 GAN UNG BAC 2 CUA DIODE

Chung ta se dung gan ung bac 2 khi muon tnh chnh xac hn cac giatr dong va the tren diode.

Hnh 2-7a ch ra gian o dong the cua 1 diode trong gan ung bac 2.Theo o, se khong co dong qua diode chng nao the tren diode cha vt quagia tr 0.7V. Hnh 2-7b cho thay mach tng ng cua diode silicon trong ganung bac 2. No gom mot cong tac noi tiep vi mot hang rao the 0.7V. Neu theThevenin ap len diode ln hn 0.7V, diode se ong (dan ien thuan). Khidiode ang dan, the ri tren diode la 0.7V oi vi moi gia tr cua dong thuan.Noi cach khac, neu the Thevenin be hn 0.7V, cong tac la h va khong codong qua diode.

Hnh 2-7: Gan ung bac 2 cua diode

V du. Dung gan ung bac 2 cua diode e tnh dong, the va cong suattieu tan tren diode cho mach hnh 2-8.


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Hnh 2-8: Mach diode gan ung bac 2

Do diode phan cc thuan, no tng ng mot pin 0.7V. ieu nay congha la the tren tai bang

VL=10V-0.7V =9.3V

Theo nh luat Ohm, dong tai bangIL=9.3V/1K=9.3mACong suat tieu tan tren diode bangPD=(0.7V).(9.3mA)= 6.51mW

II.6 NAN IEN NA CHU KY

Hnh 2-9: Mach nan ien dung diodeHnh 2-9a ch ra mach nan ien na chu ky. Nguon ac tao ra mot ien

ap xoay chieu. Gia s rang diode la ly tng. na chu ky dng cua nguonthe, diode phan cc thuan. Diode se nh mot cong tac ang ong nh hnh 2-9b. Tn hieu na chu ky dng cua nguon the se xuat hien tren ien tr tai.


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Vao na chu ky am cua nguon the, diode nh cong tac h mach, tren tai sekhong co 1 ien the nao (hnh 2-9c).

Dang song ly tng.Mach nan ien na song nh hnh 2-10a se ch lam cho diode dan trong

na chu ky dng va khong dan trong na chu ky am cua nguon ac.Hnh 2-10b la gian o dang song loi vao. No la mot song sin co gia tr

tc thi la vin va gia tr nh la Vp(in). Do o tren tai se thu c tn hieu dangna song. ieu nay cung co ngha la dong qua ien tr tai la dong mot chieu.

Hnh 2-10: Dang song cua mach nan chu ky

Tn hieu loi ra na song nh hnh 2-10c la ien the dc kieu xung. Notang t 0 en cc ai, roi lai giam ve 0, sau o tiep tuc bang 0 trong na chuky am. e co c nguon dc dung cho cac thiet b ien t, can phai loc dangtn hieu na song nay.


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Dau cham pha. e bieu th quan he ve pha tren cac cuon day cua bienthe ngi ta dung dau cham pha. Cac au day co dau cham se co cung pha.

Quan he gia the va so vong tren 2 cuon cua bien the la:V2/V1=N2/N1 (2-9)

Co the dung cong thc (2-9) cho gia tr nh, gia tr hieu dung va gia trtc thi.

V du: Tnh the tai cc ai va the tai dc cho mach hnh 2-12.

Hnh 2-12: Bien the va mach nan 1/2 chu ky

Giai: Ty so bien the la 5:1. Do o the tren cuon th cap la:V2=120/5=24V

ien the nh tren cuon th cap bang:Vp= 24/0.707 = 34V

Vi diode ly tng, the nh tren tai bang 34V.

The dc tren tai bang:Vdc=Vp/ = 34/= 10.8V

Neu dung xap x bac 2 cho diode, the nh tren tai va the dc tren taitng ng bang 33.3V va 10.6V

II.8 NAN CA CHU KY

Hnh 2-13: Mach nan ca chu ky


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Hnh 2-13 la mot mach nan ien toan song (ca chu ky). Cuon th capcua bien the co iem gia c noi at. Mach nan toan song tng ng 2mach nan na song ghep lai. V bien the co iem gia, moi mach nan co ienthe vao ch bang ien the cuon th cap. Diode D1 dan trong na chu kydng trong khi o D2 dan trong na chu ky am. Trong ca 2 na chu ky, ienthe tren tai co cung cc tnh, dong tai v vay la dong co hng. Chung ta sephan tch mot so ac iem cua tn hieu loi ra toan song nay sau ay.

Gia tr dc hay trung bnh.Do tn hieu loi ra toan song gom 2 lan tn hieu na song nen gia tr dc

cho bi:Vdc=2Vp/= 0.63Vp (2-10)

Theo (2-6) gia tr trung bnh bang 63% gia tr nh. V du, neu ien thenh la 10V th gia tr trung bnh loi ra la 6.3V.

Tan so cua tn hieu loi ra toan song la gap oi tan so nguon ac loi vao.f(out)=2f(in) (2-11)

Dong qua moi diode bang mot na dong tai:Idiode= Idc / 2

II.9 NAN CAU

Hnh 2-14: Mach nan cau

Hnh 2-14 cho thay mot mach nan cau. Mach nan cau tng t machnan toan song v no tao ra ien the loi ra toan song. Mach dung 4 diode. D1 vaD2 dan trong na chu ky dng. D3 va D4 dan trong na chu ky am.

Mach nan cau tng ng vi hai mach na song noi lai vi nhau.Trong ca hai na chu ky, the tren tai co cung cc tnh va dong tai la dong mot


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hng. Mach nay bien oi the ac au vao thanh the dc dang xung (nhapnho) loi ra.

Gia tr trung bnh va tan so tn hieu loi ra.Bi v mach nan cau tao ra tn hieu toan song nen phng trnh tnh gia

tr dc hay trung bnh cho the ra la:Vdc=2Vp/= 0.63Vp

va tan so tn hieu loi ra bangf(out)=2 f(in)

Dong qua diode trong mach nan cau bang mot na dong taiIdiode=1/2 Idc

Gan ung bac 2 cho thay rang the ra nh bang the vao nh tr i 2 lanthe ri tren diode:

Vp(out)=Vp(in)-1.4V (2-12)

II.10 CAC BO LOC

Loi ra cua cac mach nan la the dc dang xung (nhap nho). Noi cachkhac, the tren tai gom thanh phan dc va ac. Co the loc bo thanh phan ac bangcac mach loc (filter).

Co 2 loai mach loc c dung pho bien la: Mach loc LC Mach loc RC

a) Mach loc LCHnh 2-15a cho thay mach loc dung cuon L va tu C.

Hnh 2-15


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Nguon ac tao ra dong tren cuon day, tu ien va ien tr. Dong ac trencac linh kien nay phu thuoc vao cam khang cua L, dung khang cua C va R.

Cuon L co tr khangXL= 2fLTu C co dung khang bangXC=1/2fCMach loc LC c goi la thiet ke tot neu tai tan so tn hieu vao, gia tr

cua Xc nho hn RL nhieu. Khi ieu kien nay c thoa man co the bo qua RLnh mach hnh 2-15b. Mat khac ngi ta cung thiet ke sao cho tai tan so tnhieu XL ln hn XC nhieu. Ro rang rang khi o the xoay chieu tren tai se ratbe va co the xem bang 0.

Vout=(XC/XL)Vin (2-13)V du: tai tan so tn hieu Xc=100 va XL=10K th the ra ch bang

1/100 the vao. Hay mach loc a giam the xoay chieu 100 lan.

Loc loi ra cua cac mach nan

Hnh 2-16

Hnh 2-16 ch ra mach loc nam gia mach nan va tai. Mach nan co thela na song, toan song hay nan cau. e phan tch tac dung cua mach loc,chung ta dung nguyen ly chong chat. Theo o co the xem rang loi ra cua machnan co 2 thanh phan: thanh phan dc va thanh phan ac nh hnh 2-17.

Rectifier Output

timeHnh 2-17


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Chung ta noi song song vi mach loc mot tr tai RL nh hnh 2-19. Khio diode D van nap ien cho tu chu ky au tien. Trong thi gian con laicua chu ky, tu C phong qua R vi hang so thi gian R LC. Neu thoa man ieukien RLC > T (chu ky tn hieu ac) th the tren tai dng nh van la hang so,mac du co mot chut xoay chieu tren tai ma chung ta goi la the gn song(ripple voltage).

Cong thc tnh gia tr nh-nh cua the gn song la:VR = I / fC (2-14)

Trong o I la dong tai, f la tan so gn song. Neu dong tai bang 0 th thegn song VR=0.

V du, neu dong tai I=10mA, tu C=20F va mach nan cau (f=100Hz) thVR = 10mA/(100.20F)= 0.5Vpp

II.11 DIODE ZENER

Cac diode tn hieu be va nan ien ch hoat ong vung phan cc thuanma khong hoat ong vung anh thung v ieu nay se lam hong chung. Trongphan nay chung ta se xem xet diode Zener, mot diode silicon c che tao ehoat ong vung anh thung. Diode zener la thanh phan chnh cua mach onap. o la mach gi ien ap ra gan nh la hang so bat chap s thay oi cua thevao va tr tai.

Hnh 2-20: Diode Zener

Gian o IV cua diode Zener.Hnh 2-20 cho thay hnh ve cua mot diode Zener, ky hieu la Vz. Bang cachthay oi mat o pha tap, nha may co the tao ra cac Zener co ien ap anhthung t 2V en 1000V. Cac diode nay co the hoat ong 3 vung: phan ccthuan, anh thung va dong ro.


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Hnh 2-21: Gian o IV cua diode Zener

Hnh 2-21 la gian o IV cua 1 diode Zener. Trong vung phan cc thuan,khi the tren diode ln hn 0.7V no dan ien nh mot diode silicon loai thng.Trong vung ro, ch co mot dong ro rat nho qua diode. ac tuyen cua vunganh thung gan nh thang ng. Khi diode Zener b anh thung, Vz gan nhhang so. Trong bang so lieu cua nha san xuat ngi ta thng ghi Vz tai dongtest IZT nao o. Hnh 2-21 cung cho biet dong Zener toi a IZM. Trong thiet kemach diode Zener phai am bao diode Zener hoat ong dong anh thungnho hn IZM.

ien tr Zener.ien tr noi cua diode goi la ien tr Zener. ien tr Zener co gia tr

rat be. ien tr nay phan anh s kien dong Zener tang th the Zener tang. Tuynhien s tang nay rat t, c vai phan cua Von. ac tuyen vung anh thungcang doc th ien tr Zener cang be. Trong cac phan tch cua chung ta, ientr Zener b bo qua.

On ap Zener.

Diode Zener oi khi c goi la diode on ap v no co ac tnh gi ienap gia anode va cathode (Vz) la hang so bat chap s thay oi cua dong quadiode. e s dung tnh chat nay cua Zener can phai phan cc ngc no nhhnh 2-22a. Mat khac Vs phai ln hn ien ao anh thung Vz. Mot ien tr noitiep Rs c s dung e han che dong qua Zener, khong cho phep no vtqua gia tr gii han toi a.


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Hnh 2-22: on ap dung Zener

Hnh 2-22b cho thay mot cach ve khac cua hnh 2-22a, trong o machco iem noi at (Ground). Khi o e o hieu ien the gia cac iem, co theo the cua chung so vi at roi tnh ra hieu ien the gia cac iem can o.

Hnh 2-22c cho thay hnh ve loi ra cua mot bo nguon no i ti ien tr Rsva Zener. Mach nay goi la mach on ap Zener hay mach Zener.

Dong chay qua Rs bang:Is = (Vs-Vz)/Rs (2-15)

Is cung chnh la dong chay qua Zener. Phai chon Rs sao cho Is < IZM

Gan ung ly tng cua Zener la mot pin, hay mot nguon the co gia trbang Vz.

II.12 ON AP ZENER CO TAI

Hnh 2-23: on ap Zener co tai


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Hnh 2-23a ch ra mot mach on ap Zener co tai. Hnh 2-23b ch ra motmach nh the va co iem noi at. V Zener hoat ong vung anh thung, doo no gi ien ap tren tai la hang so bat chap s thay oi cua the vao va dongtai.

Gia s diode Zener khong noi vao mach hnh 2-23b. Khi o theThevenin tren tai RL la:

VTH = Vs. (RL/RS+RL) (2-16)

The Thevenin phai ln hn Vz, neu khong s anh thung se khong xayra.

Tren mach hnh 2-23, dong qua Rs bang:

IS= (Vs-Vz)/Rs (2-17)

The tren tai bang the Zener

VL=VZ (2-18)

Dong tai bang:

IL= VL/RL (2-19)

Dong Zener. Theo nh luat Kirchhoff, ta co:

IS=IL+IZ (2-20)hay dong qua Zener bang:

IZ=IS IL (2-21)

II.13 GAN UNG BAC 2 CUA DIODE ZENER


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Hnh 2-24

Hnh 2-24a cho thay gan ung bac 2 cua diode Zener. Khi o Zener nhmot nguon the ly tng Vz noi tiep vi tr Zener RZ. Tong ien the tren Zenerbang the anh thung Vz cong vi sut the qua ien tr Zener. Vay anh hngcua tr Zener len the loi ra nh the nao? Chung ta hay xet s o hnh 2-24b va

2-24c. Theo hnh 2-24c, the tai bang:

VL= VZ + IZRZ

S thay oi cua the tren tai so vi trng hp ly tng la:

V= IZRZ (2-22)

Thng V nho, c vai phan cua 1 Von.ien tr Zener cung anh hng en the nhap nho tren tai. Mach tngng khi xet en RZ cho tren hnh 2-24c.

Thanh phan xoay chieu cua the ra bang:

VR(out)=VR(in)RZ/(RZ+RS)


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Hau het cac diode thng mai co VD t 1.5V en 2.5V vi dongt 10mA en 50mA. Gia tr chnh xac cua the ri tren LED phu thuocvao dong qua LED, mau LED va mot so yeu to khac. Tr khi c chuthch, chung ta se dung VD =2V e phan tch cac mach co lien quan enLED trong giao trnh nay.

The anh thung cua LED rat be, ch c 3-5V. LED thng dunge ch th tnh trang co hay khong co nguon cua thiet b va goi la powerLED. Khi o mot diode chnh lu c mac song song ngc vi LEDe bao ve LED khoi b anh thung khi phan cc ngc.

b) Seven - Segment Display.Hnh 2-26a trnh bay mot bo ch th dung en 7 oan. No cha 7

oan LED, anh so t A en G. Moi LED la 1 oan v no la 1 thanhphan cua ky t ma no ch th. Hnh 2-26b la s o cua mot bo ch th 7oan. Cac ien tr dung e han che dong qua LED. Cac LED c noitheo kieu anode chung (cung co en 7 oan noi cathode chung). Bangcach noi at mot hoac nhieu ien tr, chung ta se nhan c cac so t 0en 9 va cac ky t nh A,b,C,d, E va F.

Hnh 2-26: Ch th 7 oan

c) PhotodiodeTrong cac phan trc chung ta biet rang, mot thanh phan trong

dong ngc cua diode la dong cac hat mang thieu so. Cac hat mang nayton tai v nang lng nhiet co the lam bat (dislodging) mot electron hoatr khoi quy ao cua no tao ra mot electron t do va mot lo trong. Thi


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u iem chu yeu cua optocoupler la s cach ien gia au vaova au ra cua he. ien tr gia au vao va ra cua optocoupler co theen hang ngan M. Optocoupler co the dung trong cac ng dung caothe, o the gia au vao va ra co the khac nhau en hang ngan von.

e) Laser diode (Light Amplification by Stimulated Emission ofRadiation)

S chuyen ngau nhien t mc nang lng cao ve mc nang lngthap cua cac electron t do trong LED lam cho anh sang phat ra t motLED co pha thay oi trong mot vung rong t 0 en 3600. Nguon sangco pha thay oi goi la nguon sang khong ket hp (Incoherent).

Trong diode laser th khac. No co the tao ra mot nguon sang kethp (Coherent), ngha la nguon sang ma tat ca cac song anh sang eucung pha vi nhau. Trong diode laser ngi ta dung buong cong hnge kch thch cac anh sang bc xa tai mot tan so vi pha duy nhat. aciem cua nguon sang do diode laser phat ra la n sac, cung pha va vvay co the hoi tu tot va co cng o ln. Cac diode laser cung c goila cac laser ban dan. Chung co the tao ra anh sang nhn thay cung nhkhong nhn thay (hong ngoai). Diode laser c dung nhieu trong cacng dung cong nghe thong tin va truyen thong.


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Chng IIITRANSISTOR

Nam 1951 William Schockley a phat minh ra transistor, con goi latransistor lng cc. Transistor la mot thiet b ban dan ma no co the khuyechai cac tn hieu ien t (dong hoac the). S kham pha ra transistor a dan enviec tao ra hang loat cac thiet b ien t va cac mach tch hp ma chung tathng goi la cac IC (Integrated Circuits). Nh co IC ma ngay nay chung taco may tnh, truyen hnh, ien thoai di ong, ngi may va v.v

III.1 CAU TAO VA CAC DONG IEN TRONG TRANSISTOR

Hnh 3-1: Cau tao cua transistor

Mot transistor co 3 vung ban dan NPN nh hnh 3-1. Vung di cung lavung Emitter (phat), vung gia goi la vung Base (goc), vung tren cung goi lavung Collector (gop). Transistor nh hnh 3-1 goi la transistor NPN.

Transistor cung c che tao di dang PNP. Hoat ong cua transistorNPN va transistor PNP ve c ban giong nhau. Trong chng nay chung ta sech phan tch transistor NPN.

Trong transistor vung emitter c pha tap nhieu. Vung base pha tap

rat t. Vung collector pha tap trung bnh.Transistor trong hnh 3-1 gom 2 moi noi PN: moi noi base-emitter vamoi noi base-collector. V vay co the xem nh transistor gom 2 diode noingc nhau. Cau hnh nay ch ung khi transistor khong phan cc. Ngi tathng dung cau hnh nay khi o th transistor. Neu 2 diode trong transistorcon tot th nhieu kha nang transistor cung con tot.


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Transistor khong phan cc giong nh 2 diode noi ngc. Moi diode comot hang rao the c 0.7V (oi vi transistor Si). Khi noi transistor vi nguonngoai, se co cac dong ien qua cac vung khac nhau trong transistor.

Hnh 3-2: phan cc transistor

Trong hnh 3-2 dau tr bieu th cac electron t do trong vung emitter.Nguon VBB phan cc thuan diode base - emitter. Trong khi nguon Vcc phancc ngc diode base - collector. Do emitter c pha tap manh, no phat cacelectron vao base. S pha tap t cua base co y ngha la lam cho hau het cacelectron t emitter khong b tai hp ma se en collector. Collector co ngha lathu gop. Cc collector co nhiem vu thu cac electron t emitter.

Khi c phan cc, neu the VBB ln hn hang rao the, cac electron t

emitter se vao vung base. Ve mat ly thuyet cac electron nay se i theo 2hng. Th nhat la vao vung base qua RB e en cc dng cua nguon VBB.Th hai la vao collector. Do s pha tap cua vung base rat t, nen hau het cacelectron di chuyen len vung collector. Tai ay no b hut ve cc dng cuanguon Vcc qua ien tr Rc.

Hnh 3-3: Ky hieu va cac dong ien trong transistor


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Hnh 3-3 ch ra ky hieu tren s o cua mot transistor.Theo nh luat Kirchhoff, ta co:

IE = I B + IC (3-1)ieu nay chng to rang: Dong cc e bang tong cua dong cc c va dong

cc b.V dong cc b rat be nen co the xem rang

IE IC (3-2)Ngi ta nh ngha He sodc cua transistor nh sau:

dc = IC / IE (3-3) ln hn 0.99 oi vi cac transistor cong suat be, con oi vi cac

transistor cong suat ln hn 0.95.Ngi ta cung nh ngha He so khuyech ai dong mot chieu

dc = IC / IB (3-4)V du: mot transistor co dong Ic =10mA, dong Ib = 40A th

dc = 10mA/ 40A = 250

III.2 NOI EMITTER CHUNG

Co 3 cach noi transistor thng dung la: Noi E chung (Common Emitter - CE) Noi C chung (Common Collector - CC) Noi B chung (Common Base - CB)

Hnh 3-4: Noi CE


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Trong hnh 3-4, phan chung la emitter v no c noi vi phan at(Ground - GND) cua 2 nguon VBB va VCC. V vay mach nay goi la mach chungemitter. Mach co 2 vong kn: vong base va vong collector.

Trong mach vong base, diode base - emitter c phan cc binguonVBB. ien tr RB e han che dong base. Bang cach thay oi VBB hoacRB chung ta co the thay oi dong base va v vay co the thay oi dongcollector. Noi cach khac chung ta co the ieu khien dong collector bang cachieu khien dong base. ieu nay rat quan trong v chung ta co the dung motdong be (dong base) e ieu khien mot dong ln (dong collector).

Lu y: Cac ch so di dung trong mach transistor co y ngha nh sau: Chung ta dung cung ch so di e bieu th nguon nuoi. V du VBB hoac

VCC. Ngc lai chung ta dung ch so di khac nhau e bieu th hieu ien

the gia cac iem. V du VCE la hieu ien the gia cc C va cc E.Ta co:

VCE = VC - VEVCB = VC -VBVBE = VB -VETrong cach noi CE, do VE = 0 nenVCE = VCVBE = VB

III.3 AC TUYEN BASE

ac tuyen base cua mot transistor giong nh cua mot diode thng nhhnh ve 3-5. V vay co the dung cac gan ung cua diode khi phan tch machbase cua transistor.

Hnh 3-5: ac tuyen base cua transistor


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Ap dung nh luat Ohm cho mach vong base, chung ta thu c:IB = (VBB-VBE)/ RB (3-5)

Xem diode ly tng th VBE=0. Trong gan ung bac 2,VBE=0.7V.

Hnh 3-6

V du: Dung gan ung bac 2 e tnh dong base trong hnh 3-6.Sut the qua RB bang bao nhieu? Tnh dong collector biet dc =200.Giai: The sut qua RB la

VB = VBB-VBE = 2V 0.7V = 1.3VDong base bangIB = (VBB -VBE)/ RB = (2V 0.7V)/ 100K = 13AVi he so khuech ai dc =200, dong collector bangIC =dc IB = 200x13A = 2.6mA

III.4 AC TUYEN COLLECTOR

ac tuyen collector la ng cong mo ta quan he gia dong I C va ienap ri tren transistor VCE.

Tren hnh 3-7a, bang cach thay oi VBB hoac VCC co the tao ra cac theva dong khac nhau tren transistor. Chang han, co nh VBB e IB =10A, thayoi VCC , o IC va VCE tng ng, chung ta co the ve ac tuyen collector nh

hnh 3-7b. So lieu c lay ng vi transistor 2N3904. Cac transistor khac cothe co so lieu khac nhng dang cua ng cong la tng t.Khi VCE bang 0 diode collector khong phan cc nen dong collector

bang 0. Khi tang VCE tang th dong IC cung tang. Dong IC at gia tr bao hoa1mA khi VCE ln hn c vai phan cua mot von.


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Hnh 3-7

Vung dong hang cua transistor tren hnh 3-7b lien quan en cau taocua transistor. Sau khi diode collector phan cc ngc, cac electron t do phatxa t emitter eu b collector thu gop. Gia tr cua dong nay ch phu thuoc so

electron phat xa t emitter hay ch phu thuoc mach base.Khi tang VCE len qua 40V, diode CB b anh thung. Khi o dong

collector tang vot. Hoat ong bnh thng cua transistor a b pha huy. Cactransistor khong c phep hoat ong che o nay v no se b hong. Cac bangso lieu cua nha san xuat ghi gia tr the anh thung collector-emitter laVCE(max)hoac BVCE.

ien ap collector va cong suat.Ap dung nh luat Kirchhoff cho mach vong collector, ta co

VCE = VCC - ICRC (3-6)

Cong suat tieu tan tren transistor bangPD = VCE.IC (3-7)

Cong suat tieu tan PD lam cho nhiet o moi noi CB tang nhanh. Congsuat tieu tan cang cao, nhiet o moi noi CB cang cao. Transistor se hong neunhiet o moi noi vt qua 150OC. Trong bang so lieu cua nha san xuat co ghiPD(max) la cong suat tieu tan toi a. e transistor hoat ong bnh thng th PDtnh theo (3-7) phai be hn PD(max).


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Theo ng ac tuyen collector, transistor co 3 vung hoat ong: Vung tac ong (active region) con goi la vung hoat. Vung anh thung (breakdown region). Vung bao hoa (saturation region).Vung tac ong cua transistor la vung co IC la hang so.Vung anh thung

ng vi VCE> 40V. Vung bao hoa cua transistor la vung co the VCE be hn 1V.Ngi ta s dung transistor vung tac ong e khuyech ai tn hieu.

Neu ve nhieu ng ac tuyen collector tren cung mot o th chung taco hnh ve 3-8.

Hnh 3-8

Tren hnh 3-8 co mot ng cong ac biet. o la ng di cung,

o IB=0 nhng van co dong IC be chay qua transistor. o la dong r cuatransistor do cac hat mang thieu so tao ra. Mien gii han bi ng cong coIB=0 va truc hoanh goi la vung ngng dan cua transistor.

Tom lai, transistor co 4 vung hoat ong: tac ong, ngng dan, bao hoava anh thung. Vung tac ong thng ng dung e khuyech ai tn hieu be.Vung tac ong con goi la vung tuyen tnh v s thay oi cua dong I C (tn hieura) ty le tuyen tnh vi s thay oi cua dong IB (tn hieu vao). Trong cac thietb ky thuat so va may tnh, transistor thng hoat ong vung ngng dan hoacbao hoa hay con goi la che o khoa (switching mode).

V du: Transistor tren hnh 3-9 co dc =300. Tnh IB , IC ,VCE va PD.Giai:

IB = (VBB-VBE)/ RB = (10V 0.7V)/ 1M = 9.3ADong collector bangIC=dc IB = 300.(9.3A)= 2.79mAThe collector bangVCE = VCC - ICRC =10V-(2.79mA)(2K)=4.42V


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Hnh 3-9

Cong suat tieu tanPD = VCE.IC = (4.42V).(2.79mA)= 12.3mW

III.5 CAC GAN UNG CHO TRANSISTOR

Hnh 3-10


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Hnh 3-10a ve s o transistor. VBE la the tren diode emitter. VCE lathe gia cac cc collector va emitter. Chung ta hay xem xet cac machtng ng cua transistor nay.

a) Gan ung ly tng. Hnh 3-10b la mach tng ng cua mot transistortrong gan ung ly tng. Mo hnh nay thng dung khi phan tch mach vinguon VBB ln. Luc nay chung ta dung gan ung ly tng cho diode emitterkhi tnh dong base.

b) Gan ung bac 2. Hnh 3-10c la mach tng ng cua mot transistor tronggan ung bac 2. Mo hnh nay thng dung khi phan tch mach vi nguonVBB be. Luc nay chung ta dung xap x bac 2 cho diode emitter khi tnhdong base. oi vi transistor Si, VBE=0.7V. Transistor Ge co VBE=0.3V.Trong gan ung bac 2, dong base va v vay dong collector khac mot chutso vi gan ung ly tng.

c) Xap x cao hn. ien tr noi cua diode emitter tr nen quan trong chtrong cac ng dung cong suat cao ma o dong rat ln. Anh hng cuaien tr noi emitter la cho the VBE co the en c 1V khi dong base ln.Cung nh diode base, ien tr noi cua diode collector co anh hng angke trong mot so ng dung. Cung vi ien tr noi emitter va collector,transistor co mot so cac hieu ng bac cao khac lam cho viec tnh toan bangtay tr nen kho khan. V ly do nay, cac tnh toan sau gan ung bac 2 canphai s dung may tnh.

Hnh 3-11

V du 1: Dung gan ung ly tng tnh the VCE cua transistor trong machhnh 3-11.

Transistor ly tng co ngha la VBE=0. Do o dong base bangIB = 15V/ 470K = 31.9ADong collector bangIC= 100(31.9A)= 3.19mAThe collector-emitter cua transistor bang


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VCE = 15V (3.19mA)(3.6K)= 3.52VTrong cac tnh toan, t khi phai tnh dong emitter. ay, chung ta th

tnh dong emitter. No bangIE=IC+IB= 3.19mA + 31.9A = 3.2mACo the thay rang IE ICV du 2: Dung gan ung bac 2 tnh the VCE cua transistor trong mach

hnh 3-11.Transistor gan ung bac 2 co VBE=0.7V, do o dong base bangIB = 14.3V/ 470K = 30.4ADong collector bangIC= 100(30.4A) = 3.04mAThe collector - emitter cua transistor bangVCE = 15V - (3.04mA)(3.6K) = 4.06VNhan xet:S khac nhau cua VCE trong gan ung ly tng va gan ung bac 2 la c

0.5V. Tuy thuoc vao ng dung ma chung ta s dung gan ung hp ly.

III.6 S THAY OI CUA HE SO KHUYECH AI DONG IEN

He so khuyech ai dong ien cua transistor phu thuoc vao 3 yeu to: loai transistor dong collector nhiet oV vay Bang so lieu cua transistor 2N3904 cho thay hfe min=100 va

hfemax=300 tai nhiet o 250C va dong collector 10mA. Neu chung ta lap rap

hang ngan mach transistor 2N3904 chung ta se nhan c he so khuyech aidong be nhat la 100 va ln nhat la 300.

Anh hng cua dong collector va nhiet o oi vi he so khuyech ai cothe thay ro qua bang so lieu sau:

IC (mA) hFE (min) hFE (max)0.1 40 -1 70 -10 100 30050 60 -100 30 -


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Ro rang rang 2N3904 se hoat ong tot nhat tai dong IC=10mA.

III.7 NG TAI (LOAD LINE)

Hnh 3-12 la mach transistor noi CE. Cho cac gia tr cua RB, dc chungta co the tnh dong IC va the VCE .

Hnh 3-12

S phan cc base. Hnh 3-12 la mot v du ve mach phan cc base mano co ngha la tao ra mot dong base co nh. V du, neu RB=1M th dongbase bang 14.3A (gan ung bac 2). Dong nay luon xap x gia tr 14.3A khichung ta thay the transistor khac va ngay ca khi nhiet o thay oi.

Neu dc=100 th dong collector xap x 1.43mA va the collector - basebang:

VCE = VCC - ICRC =15V (1.43mA).(3K)=10.7VVay iem tnh Q (quiescent) xac nh dong va the tren transistor la

IC = 1.43mA va VCE=10.7V

Phng phap o th. Chung ta co the tm iem Q bang phng phap oth da tren ng tai (load line) cua transistor. ng tai la ng cong choquan he IC va VCE cua mot transistor theo phng trnh sau

VCE = VCC - ICRCHay

IC = (VCC -VCE)/ RC (3-8)(3-8) la mot phng trnh tuyen tnh va o th cua no la mot ng

thang. ng nay goi la ng tai v no phan anh s anh hng cua RC len ICva VCE.Theo (3-8), vi VCC =15V, RE = 3K ng tai cat truc tung taiIC = VCC/RE = 15V/3K = 5mAva cat truc hoanh taiVCE =VCC =15VHnh 3-13 cho thay ng thang nay.


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Hnh 3-13

ng tai cho thay iem tnh Q co the nhan nhng gia tr kha d nao.Noi cach khac, ng tai cho biet tat ca cac kha nang kha d cua iem Q.

iem bao hoa. Khi RB be dong IC rat ln lam cho the VCE cua transistorat gia tr xap x 0V. Trong trng hp nay, transistor a trang thai bao hoa,ngha la dong IC a tang en gia tr cc ai kha d.

iem bao hoa la iem ma o ng tai tiem can vi vung bao hoacua transistor. V VCE rat be nen iem bao hoa nam gan au tren cua ngtai. iem bao hoa cho thay dong collector a at c gia tr cc ai kha doi vi mach ang xet. V du, tren mach hnh 3-14a transistor vao trang thaibao hoa khi IC =5mA, luc nay VCE xap x 0V.

e tm ra dong IC bao hoa chung ta hnh dung ngan mach cc C va ccE cua transistor nh hnh 3-14b. V VCE = 0V nen toan bo nguon VCC=15Vc at len RC. Vay dong IC bao hoa bang 5mA.

Bieu thc tnh dong bao hoa cua transistor laIC(sat) = VCC/ RE (3-9)

iem ngng dan (CUTOFF POINT). iem ngng dan la iem ma tai ong tai tiem can vi vung ngng dan cua transistor. V dong collector taiiem cutoff rat be nen iem cutoff gan vi au cuoi phia di cua ng tainh hnh 3-13. iem cutoff cho thay the VCE cc ai oi vi mot mach. e tmiem cutoff chung ta hnh dung transistor h mach gia cc C va cc E nhhnh 3-14c, khi o the VCE cc ai kha d la 15V, bang gia tr cua nguon cungcap VCC. Khong co dong IC nen nguon VCC at het len cc C va E cuatransistor.


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VCE(cutoff) = VCC (3-10)

Hnh 3-14: Tm 2 iem au cuoi cua ng tai

V du: Tnh dong bao hoa va the cutoff cho mach hnh 3-15

Hnh 3-15

IC(sat) = VCC/ RE = 30V / 3K = 10mAVCE(cutoff) = VCC =30V


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III.8 IEM LAM VIEC VA CAC CHE O CUA TRANSISTOR

Moi mach transitor co mot ng tai. Cho mot mach transistor bat ky cothe tnh dong bao hoa va the ngng dan. Chung chnh la cac iem tng ngtren truc tung (IC(sat) ) va tren truc hoanh (VCC ) cua ng ganh.

Hnh 3-16 ch ra mot mach phan cc base vi RB=500K. ng tai iqua IC(sat) = 5mA va VCC = 15V (the gia C va E khi transistor ngng dan).

Gia s transistor la ly tng, dong base bangIB=15V/500K = 30A.

Hnh 3-16

Neu he so khuech ai dong la 100 th dong collector bangIC=100.30A= 3mA

The VCE cua transitor bang

VCE= 15V-(3mA)(3K) = 6VVay transistor tren mach hnh 3-16 co iem lam viec Q xac nh bihai tham so

IC= 3mA va VCE= 6VGoi la iem Q (quiscent) v no xac nh bi the va dong DC (tnh) cua

transistor. iem Q cua transistor co the thay oi v nhieu ly do. Chang han heso khuyech ai dong thay oi t 50 en 150 nhng IB khong oi va bang 30Ath dong IC thay oi t 1.5mA en 4.5mA va v vay the VCE se thay oi t10.5V en 1.5V. Neu dc thay oi nhieu hn na, iem Q co the ri vao vung

bao hoa hoac ngng dan va transistor trong mach se khong con khuyech aitn hieu na.Ro rang la iem Q cua mach phan cc base rat nhay vi s thay oi

cua dc . Ngi ta co the khac phuc nhc iem nay bang cac mach phan ccloai khac.

Co 2 che o lam viec cua cac transistor la: Che o khuyech ai


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Che o cong tac (switch)Trong che o khuyech ai, iem Q phai trong vung tac ong di

moi ieu kien. Trong che o switch, transistor chuyen gia 2 trang thai baohoa va ngng dan. Viec phan tch hoat ong cua transistor che o switch sec trnh bay trong phan sau ay.

III.9 TRANSISTOR SWITCH

Mach phan cc base thng c dung trong cac mach so (digitalcircuits) v chung c thiet ke e transistor lam viec vung bao hoava ngng dan. iem Q cua cac transistor trong mach so chuyen giavung bao hoa va ngng dan ma khong trong vung khuyech ai. Trongtrng hp nay s thay oi cua Q khong quan trong.

Hnh 3-17 la s o mot mach transistor lam viec che o khoa.Trong o transistor c phan cc base che o bao hoa sau (dongphan cc base ln v vay lam cho dong collector ln hn dong collectorbao hoa).

Hnh 3-17

Khi SW ong, dong base xap x 1mA (ln hn dong base can

thiet e transistor bao hoa) va lam cho transistor bao hoa sau. V vaythe VCE=0. Khi SW h, khong co dong base va v vay VCE=VCC

The loi ra (Vout) cua mach transistor trong che o SW co 2 trangthai: ien the cao (bang VCC) va ien the thap (0V). Lu y rang gia trchnh xac cua the loi ra trong mach switch khong quan trong ma quantrong la cho 2 trang thai nay phai khac nhau (phan biet c).


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Mach khoa con goi la mach 2 trang thai tng ng vi 2 trangthai cua loi ra.

V du: neu nguon VCC trong mach 3-17 giam con 5V va dong rocollector la 50nA. Tnh the loi ra 2 trang thai biet rang the bao hoacua transistor la VC (sat)=0.15V.

Khi transistor ngng dan the tren transistor bangVCE=5V- (50nA)(1K)=4.99995VKhi transistor bao hoa, the VCE=VCE(sat) =0.15V

Tr khi la nha thiet ke, chung ta se khong quan tam en gia tr chnhxac cua the ra trong cac mach so. Van e la cho the ra phai co 2 giatr phan biet (gan 5 V khi ngng dan va xap x 0V khi bao hoa).

III.10 PHAN CC EMITTER

Trong cac mach khuyech ai chung ta can mach transistor maiem Q co kha nang on nh hay khong b anh hng bi s thay oicua dc.

Hnh 3-18

Hnh 3-18 cho thay mot mach phan cc emitter trong o ien tra c chuyen t mach base sang mach emitter. iem Q cua mach

nay rat on nh. No hau nh khong thay oi khi dc thay oi t 50 en150.

Nguon VBB bay gi ap trc tiep vao base. The cc E cho biphng trnh

VE=VBB-VBE (3-11)Neu VBB > 20VBE , gan ung ly tng se cho ket qua chnh xac.

Neu VBB < 20VBE , se phai dung gan ung bac 2.


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Chung ta hay tnh cac thong so cua mach phan cc emitter trenhnh 3-19. V VBB =5V, chung ta se dung xap x bac 2. Khi o

VE = 5V - 0.7V = 4.3VDong emitter bangIE = 4.3V/2.2K = 1.95mAieu nay cung co ngha la IC xap x 1.95mA.

Hnh 3-19

Dong IC nay se tao mot sut the 1.95V tren RC. Do o the tai C so vi atbang:

VC = 15V 1.95V = 13.1VT nay tr i, chung ta goi the cua collector so vi at la the collector.Hieu ien the ri tren transistor bang

VCE = 13.1V 4.3 V = 8.8V

Vay mach phan cc emitter tren hnh 3-19 co iem Q xac nhnh sau: IC= 1.95mA va VCE=8.8VChung ta hay xem mach chong lai s thay oi cua he so khuyech

ai dong ra sao? Qua trnh tnh toan e tm ra iem Q a cho thay ieuo. Thc vay, e tm ra iem Q cua mach phan cc emitter chung ta a:

tnh the emitter tnh dong emitter tm the collector tr the collector cho the emitter e co c the VCE.

Trong qua trnh tnh Q chung ta khong s dung dc. ieu o co ngha lagia tr dc khong anh hng en gia tr cua Q. Tren thc te chung ta aco nh the emitter va do o co nh dong emitter. V vay ket qua laiem Q khong thay oi khi dc thay oi. Mot cach chnh xac th dc coanh hng ti iem Q nh phan tch sau ay.


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Anh hng cua he so khuyech ai dongdc co anh hng nho len dong collector. Di moi ieu kien hoatong, cac dong trong transistor quan he vi nhau bi phng trnh

IE=IC+IBhay

IE=IC+IC/dcVay

IC =(dc / (dc +1))IEai lng dc/(dc +1) goi la he so sai so. Neu dc =100 th dong

IC bang 99% dong IE . Vay khi ta noi dong IC bang dong IE th sai so la1%.

III.11 PHOTOTRANSISTOR

Phototransistor giong het nh photodiode nhng rat nhay. Dongra cua phototransistor ln hn dong vao dc lan.

Hnh 3-20

Nhng phototransistor co toc o cham hn photodidoe. Motphotodiode co dong ra c nA nhng co the on/off c ns. Trong khi odong ra cua phototransistor c mA nhng toc o on/off c s.

Hnh 3-20 la s o mot phototransistor noi vi mot LED. Thiet bnay goi la Optocoupler hay con goi la isolator. No cach ly gia au vaova au ra nhng moi s thay oi cua the vao Vs eu phan anh the ratren collector cua transistor. That vay, nguon Vs thay oi lam cho dongqua LED thay oi va v vay lng anh sang en cc B phototransistorthay oi. Ket qua la dong IC cua transistor thay oi va the VC thay oi.


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V du: Hnh 3-21 la s o nhan biet thi iem the xoay chieu quagia tr 0V (zero crossing) nham ong bo hoat ong cua 1 so thiet b vitan so ien li. u iem cua s o la khong can bien the cach ly giaau vao va au ra. Phototransistor chnh la mach cach ly.

Bo qua sut the tren cac diode nan, dong qua LED bangILED = 1.411(115V)/16K = 10.2mAGia tr bao hoa cua dong phototransistor laIC(sat) = 20V/ 10K = 2mA

Hnh 3-21

Khi xay ra zero crossing, dong qua LED bang 0 va v vayphototransistor ngng dan. Tai collector chung ta thu c the cao bangnguon cung cap.


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Chng IVPHAN CC TRANSISTOR

IV.1 PHAN CC BANG CAU CHIA THE

Hnh 4-1a la mach phan cc transistor c dung rat pho bien trong cacng dung: phan cc bang cau chia the. Mach phan cc la cau chia the gom 2ien tr R1 va R2. V vay mach goi la mach phan cc bang cau chia the. TiengAnh la Voltage Divider Bias (VDB).

a) b) c)Hnh 4-1: Phan cc VDB

Phan tch n gian (simplified analysis). Trong mach VDB c thietke tot dong base nho hn dong chay qua cau chia the. Do o dong base anhhng khong ang ke len cau chia the. V vay co the ngat mach base khoi cauchia the e co mach tng ng nh hnh 4-1b. Trong mach nay, the ra cua

cau chia the bangVTH= (R2VCC)/(R1+R2)Ly tng th VTH chnh la nguon nuoi mach base VBB nh hnh 4-1c.Phan cc bang cau chia the thc chat la phan cc emitter. Noi cach

khac hnh 4-1c la mach tng ng cua hnh 4-1a. Vay mach phan cc VDBtao ra dong emitter co nh. Do o mach phan cc VDB co iem Q khong phuthuoc dc.


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Co mot sai so nho trong cach tiep can n gian nay. Chung ta se phantch no trong cac phan sau. iem mau chot (crucial) ay la: trong mot machVDB c thiet ke tot, sai so khi s dung mach tng ng hnh 4-1c la ratbe. Noi cach khac, cac nha thiet ke chon la co can nhac cac gia tr linh kiensao cho mach hnh 4-1a giong nh mach hnh 4-1c.

Ket luan: Trong mach phan cc VDB, sau khi tnh VBB, phan tnh toancon lai giong het nh cac bc tnh cho mach phan cc emitter chng 3. ay chung ta liet ke ra cac phng trnh co the dung khi phan tch mach VDB.

VBB=(R2/(R1+R2))VCC (4-1)VE=VBB -VBE (4-2)IE=VE/RE (4-3)IC IE (4-4)VC = VCC - ICRC (4-5)VCE = VC - VE (4-6)

Cac bc phai lam la: Tnh the VBB cua cau chia the Tr 0.7V e co the emitter Chia cho ien tr emitter e co dong emitter Gia s dong collector xap x dong emitter Tnh the collector so vi at bang cach tr VCC cho sut the tren RC Tnh the VCE bang cach tr VC cho VE

V du: Tnh VCE cho mach hnh 4-2.

Hnh 4-2

Cau chia the tao ra the khong tai bangVBB= (2.2K / (10K+2.2K) )10V = 1.8VVE= 1.8V - 0.7V =1.1VDong emitter bangIE = 1.1V/1K = 1.1mA


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V dong collector xap x dong emitter nen the collector so vi at bangVC = 10V (1.1mA)(3.6K)= 6.04VHieu the gia collector va emitter bangVCE = 6.04V 1.1V = 4.94V

IV.2 PHAN TCH CHNH XAC MACH VDB

Chung ta bat au phan nay bang nh ngha mach VDB c thiet ketot. o la mach ma trong o cau chia the to ra manh (stiff) oi vi tr khangvao cua mach base.

ien tr nguon. Trong chng 1 chung ta a noi en nguon the manhnh sau:

Nguon the manh co RS


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Cau chia the manhNeu transistor tren mach hnh 4-3c co dc =100 th dong collector ln

hn dong base 100 lan hay dong emitter cung ln hn dong base 100 lan. Nhnt phia base, tr emitter 100 lan ln hn. Tong quat, khi nhn t base ien tremitter ln hn dc lan.

RIN=dcRE (4-8)Phng trnh (4-7) co the viet lai nh sau

R1//R2


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Hnh 4-5

iem Q mi la Q L (0.5mA,7.1V)Ngc lai neu giam RE con 510 th dong emitter va the collector mi la:

IE = 1.1V/ 510 = 2.15mAVC = 10V (2.15mA)(3.6K)=2.26VVCE= 2.26V-1.1V = 1.16VTrong trng hp nay iem Q mi la QH (2.15mA, 1.16V)

iem Q gia ng tai.Cac gia tr VCC, R1, R2, RC euco anh hng en iem Q. Trong thiet

ke thng ngi ta chon cac gia tr nay theo yeu cau cho trc. Khi o neu RE

thay oi se lam cho Q dch chuyen tren ng tai. Neu RE qua ln iem Q sedch en vung ngng dan. Neu RE qua be iem Q se dch en vung bao hoa.e at c s on nh, iem Q thng c chon gia ng tai cho machkhuyech ai.

IV.4 PHAN CC EMITTER DUNG 2 NGUON NUOI

Mot so thiet b ien t co bo nguon 2 cc tnh: nguon dng va nguonam. V du, mach hnh 4-6 ch ra mot transistor co 2 nguon nuoi: +10V va2V. Nguon am 2V phan cc thuan cho diode emitter. Nguon dng +10Vphan cc ngc cho diode collector. Mach phan cc nay la mach phan ccemitter. Do o no co ten la mach phan cc emitter 2 nguon nuoi (Two SupplyEmitter Bias = TSEB).


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Hnh 4-6

Trong cac mach TSEB thiet ke ung, dong base rat be v vay the basexap x 0V nh hnh 4-7.

Hnh 4-7

Hieu the gia 2 au RE laRE = -0.7V- (-2V)= +1.3VDong IE bangIE = 1.3V/ 1K = 1.3mADong IC xap x IE chay qua RC do o the tai cc C cua transistor bangVC = 10V (1.3mA)(3.6K) = 5.32V

The VCE= VC-VE = 5.32V-(-0.7V)=6.02V

Tom lai, khi mot mach TSEB thiet ke tot, no tng ng vi machphan cc VDB va neu thoa man qui tac 100:1 tc la

RB


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VB = 0V (4-13)IE =(VEE - 0.7V)/RE (4-14)VC =VCC -ICRC (4-15)VCE=VC +0.7V (4-16)

IV.5 CAC PHAN CC KHAC

Trong phan nay chung ta xem xet mot so kieu phan cc khac. Viecphan tch chi tiet cac kieu phan cc nay la khong can thiet v chung t cdung trong cac thiet ke mi.

a) Phan cc phan hoi emitterNhc iem chnh cua phan cc base tren hnh 4-8a la Q thay oi theo

dc. e khac phuc ngi ta dung mach phan cc phan hoi emitter nh hnh 4-8b. Y tng chnh la a vao ien tr emitter e chong lai s troi cua Q khidc thay oi. Cu the la khi IC tang lam cho VE tang -> VB tang -> IB giam ->IC giam. S phan hoi nay la phan hoi am (negative feedback). Goi la phanhoi v s thay oi the emitter c phan hoi tr lai the base. Mac khac, phanhoi la am v sau qua trnh phan hoi, dong IC thay oi ngc lai vi s thay oiban au. Vay phan hoi am tao ra s on nh.

Hnh 4-8: Phan cc phan hoi emitter

Sau ay la cac phng trnh dung cho mach phan cc phan hoi emitter.


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IE= (VCC-VBE)/(RE+RB/dc) (4-17)VE=REIE (4-18)VB=VE+0.7V (4-19)VC=VCC-RCIC (4-20)Y nh cua phan cc phan hoi emitter la loai bo dc khoi phng trnh

(4-17) bang cach chon RE>RB/dc. Neu ieu kien nay thoa th (4-17) khongphu thuoc dc.

Hnh 4-9 la mot mach phan cc phan hoi emitter cu the. Tren thc tephan cc nay khong tot hn phan cc base.

Hnh 4-9

b) Phan cc phan hoi collector

Hnh 4-10: Phan cc phan hoi collector

Hnh 4-10 ch ra mach phan cc phan hoi collector, con goi la mach tphan cc. Y tng c ban la co on nh iem Q bang cach phan hoi mot ienthe ve base e bu lai s thay oi cua dong collector. V du IC tang -> VCgiam -> VB giam -> IB giam > IC giam.


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Sau ay la cac phng trnh dung cho mach phan cc phan hoi collectorIE= (VCC-VBE)/(RC +RB/dc) (4-21)VB=0.7V (4-22)VC=VCC-ICRC (4-23)iem Q nam gia ng tai neu chonRB=dcRC (4-24)Mach phan cc phan hoi collector co tac dung on nh iem Q tot hn

phan cc phan hoi emitter. Mac du van co s troi cua Q theo dc nhng machphan cc nay thng c dung v s n gian.

c) Phan cc phan hoi collector va emitterPhan cc phan hoi emitter va phan hoi collector la nham on nh iem

Q. Mac du y tng la tot nhng s phan hoi lai khong u e on nh Q theodc. Hnh 4-11 la mot mach phan cc trong o s dung ca 2 loai phan hoi:phan hoi emitter va phan hoi collector nham cai thien o on nh cua Q.

Hnh 4-11

Sau ay la cac phng trnh dung cho mach phan cc phan hoi emitter -collector.

IE= (VCC -VBE)/(RC +RB/dc) (4-25)VE=REIE (4-26)VB=VE + 0.7V (4-27)VC=VCC-RCIC (4-28)

IV.6 TRANSISTOR PNP


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Hnh 4-12: Transistor PNP

Hnh 4-12 ch ra cau truc , ky hieu va mo hnh tng ng cuatransistor PNP. Cung giong nh transistor NPN, tong dong trong transistor tuantheo nh luat Kirchhoff.

Mach cho transitor PNP (xem hnh 4-13) hoan toan giong mach chotransistor NPN. Ch co 2 ieu khac biet:

Transistor la loai PNP Nguon am

Hnh 4-13: Mach transistor PNP


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Chng VCAC CHE O AC CUA TRANSISTOR

V.1 KHUYECH AI PHAN CC BASETrong phan nay chung ta se phan tch mach khuyech ai phan cc base.

Mac du mach khuyech ai base khong pho bien trong cac san pham ien tnhng cac y tng c ban cua no c dung nhieu trong cac mach khuyech aiphc hp khac.

TU NOI

Hnh 5-1

Hnh 5-1a la mot nguon the ac c noi ti au vao cua mot mach RC.Cau hnh nay la mach tng ng au vao cua nhieu mach khuyech ai. V

tr khang cua tu ty le nghch vi tan so nen tu C ngan can hoan toan thanhphan dc cua nguon va ch truyen thanh phan ac. tan so u cao th tr khangcua tu be do o hau het thanh phan ac cua nguon xuat hien tren R. Trongtrng hp nay tu C goi la tu noi v no noi hoac chuyen tn hieu ac en R. Vaitro cua tu C la cho phep truyen thanh phan ac t nguon en mach khuyech aima khong lam thay oi iem Q cua mach.

e cho mot tu C co the xem la tu noi th tai tan so tn hieu thap nhat, trkhang cua tu phai be hn nhieu so vi R. Ngi ta nh ngha

Tu noi tot neu thoa ieu kien:

XC < 0.1R (5-1)Ngha la tr khang cua tu C phai be hn 10 lan R tai tan so hoat ong

thap nhat.Khi thoa man qui tac 10:1, hnh 5-1a co the thay bang hnh 5-1b. Noi

cach khac oi vi cac mach thoa qui tac 10:1 co the thay the tat ca cac tu noi Cbang mot ngan mach oi vi thanh phan ac.


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Hnh 5-4

HE SO KHUYECH AI THE

He so khuyech ai the cua mot mach khuyech ai la ty so the ac loi rachia cho the ac loi vao.A=Vout/ Vin (5-2)

V du, neu the tren tai la 50mV trong khi the vao la 100V thA= 50mV/ 100V = 500A=500 co ngha la the ra ln hn the vao 500 lan.

V.2 KHUYECH AI PHAN CC EMITTER

TU THONG DAN

Hnh 5-5

Tu thong dan tng t tu noi bi v no hanh x nh la h mach oi vithanh phan dc va ngan mach oi vi thanh phan ac. Nhng tu thong dankhong dung e noi tn hieu gia 2 iem ma no dung e tao ra mot at ac.

Hnh 5-5a cho thay mot nguon the ac c noi ti mot ien tr va mottu. tan so cao, tr khang cua tu rat be v vay toan bo nguon the ac coi nh


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c at tren R. Noi cach khac, iem E la c noi at ve mat ac. Trongtrng hp nay tu C goi la tu thong dan v no cho phep noi iem E vi at vemat ac. Tu thong dan cho phep chung ta noi mot iem nao o vi GND makhong lam thay oi Q.

ieu kien e mot tu c xem la thong dan tot laXC < 0.1R (5-3)

Khi (5-3) thoa th mach hnh 5-5a co the thay bang mach hnh 5-5b.

KHUYECH AI VDB

Hnh 5-6

Hnh 5-6 cho thay mot mach khuyech ai VDB. e tnh the va dongDC, chung ta tng tng rang tat ca cac tu eu h mach. Khi o mach tngng nh mach phan cc VDB. Gia tr dc hay gia tr tnh cho mach nay nhsau:

VB=1.8VVE=1.1VVC=6.04VIC=1.1mANh a phan tch tren ay, chung ta dung cac tu noi e noi the nguon

vi base, noi the collector vi tai. Chung ta cung dung tu thong dan giaemitter va at. Y ngha cua tu nay la cho: No lam tang he so khuyech ai thecua transistor so vi khi khong co tu (cac phan sau se phan tch ro hn).

Trong hnh 5-6, nguon the ac la 100V. No c a vao base. Do tuthong dan CE toan bo the nay c at len diode base emitter. Tai collectorchung ta thu c the base nhng a c khuyech ai.


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DANG SONG VDBTren hnh 5-6, nguon the ac au vao la ieu hoa va thanh phan dc bang

0. The base la chong chat cua the ac loi vao va thanh phan dc 1.8V. The ac collector la the au vao a c khuyech ai ao pha chong chat vi thanhphan dc bang 6.04V. The tren tai giong nh the collector vi thanh phan dcbang 0.

V.3 CHE O TN HIEU BE

Hnh 5-7

Hnh 5-7 ch ra gian o dong the cua diode base emitter. Khi nguon theac c noi ti cc base cua transistor, mot the ac se xuat hien tren diodebase. ieu nay tao ra s bien thien tuan hoan tren VBE nh hnh 5-7.

IEM LAM VIEC TC THI.Khi the vao thay oi, iem lam viec tc thi di chuyen t v tr Q ban

au len pha tren hoac xuong pha di. The base emitter tong cong gom theac va thanh phan dc. Bien o cua the ac quy nh bien o thay oi cua Q. Thebase ac ln tao ra s bien ong ln cua Q, the base be tao ra s bien ong becua Q.

S SAI DANGThe base tao ra dong emitter cung tan so nh hnh 5-7. Neu nguon the

base ac la ieu hoa, dong emitter cung ieu hoa. Nhng dong emitter khong la


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ieu hoa ly tng v quan he dong emitter the base khong hoan toan la ngthang. ieu nay tao ra s sai dang (meo) tn hieu ma chung ta khong mongmuon trong cac he thong Hi-Fi (High Fidelity).

e giam thieu s sai dang ngi ta dung cac cach sau: Gi the base be. Khi o quan he base- emitter cua transistor la tuyen tnh. Qui tac 10:1.

Tong dong emitter bangIE= IEQ+ ieTrong o IEQ la dong emitter phan cc con ie la dong emitter ac. e

giam thieu s sai dang, gia tr nh cua dong ie phai be hn dong emitter tnh10 lan theo qui tac 10:1 sau ay.

Tn hieu be: iepp


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Hnh 5-8

Hnh 5-9

Hnh 5-9 cho thay quan he dong the cua diode emitter.Ta co:IE=IEQ+ie

VBE= VBEQ+vbe


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IEN TR AC CUA DIODE EMITTERTren hnh 5-9 s thay oi ieu hoa cua VBE tao ra s thay oi ieu hoa cua IE.Gia tr nh nh cua ie phu thuoc iem Q. Do quan he dong the emitter lang cong nen vi vbe co nh, dong ie ln hn neu iem phan cc Q nam pha cao hn. Noi cach khac, ien tr ac cua emitter giam khi dong emitter dctang.

ien tr emitter ac c nh ngha nh sau:re = vbe / ie (5-7)Theo vat ly chat ran,ien tr ac cua emitter co the tnh qua cong thc

n gian sau:re = 25mV / IE (5-8)Sau nay se thay, gia tr cua re co anh hng en he so khuyech ai the

cua mach transistor.

V.5 HAI MO HNH CUA TRANSISTOR

e mo ta hoat ong cua mach khuyech ai transitor che o ac, canmot mach tng ng cho transistor. Noi cach khac chung ta can mot mo hnhcho transistor ma no mo phong c hoat ong cua transitor khi co tn hieu ac.

Mot trong nhng mo hnh transistor sm nhat do Ebers Moll e xuat lamo hnh tren hnh ve 5-10. Mo hnh nay con goi la mo hnh ch T.

Hnh 5-10: Mo hnh ch T cua transistor


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mo hnh . Sau ay chung ta se dan ra cac mach tng ng ac cua cac machkhuyech ai phan cc base va phan cc VDB.

a) MACH KHUYECH AI PHAN CC BASE

Hnh 5-14

Hnh 5-14a la mot mach khuyech ai phan cc base. e co mach tngng ac, chung ta ngan mach tat ca cac tu. iem co nhan Vcc cung c noiat ve mat ac. Hnh 5-14b cho thay mach tng ng ac. Transistor a ucthay the bi mo hnh . Trong mach base, the ac loi vao at tren RB song songvi re . Trong mach collector, nguon dong ic chay qua RC va RL mac song

song.

b) MACH KHUYECH AI VDBHnh 5-15a la mot mach khuyech ai VDB. Hnh 5-15b cho thay mach

tng ng ac. Transistor a uc thay the bi mo hnh . Trong mach base,the ac loi vao at tren R1 song song vi re va vi R2. Trong mach collector,nguon dong ic chay qua RC va RL mac song song.


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Theo (5-13) he so khuyech ai the bang ien tr ac collector chia choien tr ac cua diode emitter.

Hnh 5-16

Co the thay rang t mach tng ng 5-16c chung ta cung se thu cket qua tng t.

Hnh 5-17

V du: Cho mach hnh 5-17. Tnh A va the tren tai RL.Giai: Tr collector ac bang

rc = RC//RL = (3.6K//10K)=2.65K

Gia s transistor co re =22.7, ta coA=rc/re = 2.65K/ 22.7 = 117

The tren tai bangvout = Avin = 117.(2mV) = 234mV


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Hnh 5-19a cho thay mot mach khuyech ai gom 2 tang. Tn hieu ra cuatang th nhat (ao pha so vi tn hieu vao) c a vao tang th hai. Tren taiRL chung ta thu c tn hieu cung pha vi tn hieu loi vao nhng a ckhuyech ai nhieu lan.

Hnh 5-19b cho thay mach tng ng ac. Tr khang collector ac cuatang th nhat la

rc = RC// zin(stage)He so khuyech ai cua tang th nhat bangA1 = (RC// zin(stage) )/ reHe so khuyech ai cua tang th hai bangA2 = (RC// RL)/ reHe so khuyech ai cua toan mach bang

A=A1A2 (5-15)

V.10 KHUYECH AI CE CAI TIEN

He so khuyech ai the A cua mach khuyech ai CE phu thuoc vao dongtnh, s thay oi cua nhiet o va ban than transistor.

Mot phng phap nham on nh he so A la chen mot ien tr re trongmach emitter nh hnh ve 5-20a.

Hnh 5-20a


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A= Rf / re +1 (5-20)Thng Rf / re >>1 nen (5-20) tr thanh

A= Rf / re (5-21)Y ngha cua (5-21) la cho: he so A ch phu thuoc cac ien tr trongmang phan hoi Rf va re ma khong phu thuoc cac yeu to khac.


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Chng VIKHUYECH AI CONG SUAT

VI.1 THUAT NG BO KHUYECH AICo nhieu cach khac nhau e phan loai mot mach khuyech ai. Chang

han co the phan loai theo che o hoat ong, phan loai theo kieu noi gia cactang, phan loai theo dai tan so, mc tn hieu

PHAN LOAI THEO CHE O HOAT ONGChe o A (hang A). Trong che o nay, transistor hoat ong trong vung

tac ong. Trong che o A, cac nha thiet ke chon iem Q gia ng tai.

Theo cach nay tn hieu co the co bien o toi a ma khong b meo do transistorbao hoa hoac ngng dan.Che o B (hang B). Trong che o nay, transistor c phan cc sao

cho iem Q nam bien gii vung tac ong va vung ngng dan. Transistor chdan na chu ky dng cua nguon ac. ieu nay lam giam nhiet hao ph trentransistor cong suat.

Che o C (hang C). Trong che o nay, transistor c phan cc saocho iem Q nam sau trong vung ngng dan. Transistor ch dan mot phan cuana chu ky dng cua nguon ac. Ket qua la tai collector chung ta ch nhan

c mot xung ngan.PHAN LOAI THEO KIEU NOI TANG

Hnh 6-1


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Hnh 6-1a la s o noi tang bang tu. Tu noi truyen tn hieu a ckhuyech ai en tang tiep theo. Hnh 6-1b la s o noi tang bang bien the.The ac c ghep qua bien the va truyen en tang tiep theo.

Trong hai cach noi tren ay, thanh phan dc c cach ly hoan toan giacac tang khuyech ai. Hnh 6-1c la s o noi tang trc tiep. Trong o collectorcua transitor th nhat c noi trc tiep en base cua transistor th hai. Trongcach noi trc tiep, ca thanh phan ac lan thanh phan dc eu c noi. Tn hieudc c ghep t tang th nhat sang tang th hai ma khong b mat mat.Khuyech ai ghep trc tiep con goi la khuyech ai dc.

PHAN LOAI THEO MIEN TAN SOMot cach khac e phan loai mach khuyech ai la dung tan so. V du,

khuyech ai am tan (audio amplifier) ch cac mach khuyech ai trong vungtan so t 20Hz en 20KHz. Khuyech ai cao tan (Radio Frequency) e ch cacbo khuyech ai co tan so tren 20KHz. Chang han khuyech ai RF trong cacradio AM khuyech ai cac tn hieu t 535KHz en 1605KHz. Khuyech ai RFtrong cac radio FM khuyech ai cac tn hieu t 88MHz en 108MHz.

Theo tan so ngi ta cung phan loai khuyech ai band hep va khuyechai band rong. Khuyech ai band hep ch khuyech ai tn hieu trong mot vungtan so, chang han t 450 KHz en 460KHz. Khuyech ai band rong khuyechai tn hieu trong mot vung tan so rong chang han t 0 en 1MHz. Khuyechai band hep con goi la khuyech ai RF cong hng. Tai cua mach khuyechai la mach cong hng LC. No thng dung trong cac mach chon kenh trongradio hoac TV.

PHAN LOAI THEO MC TN HIEUChung ta a xem xet hoat ong cua transistor che o tn hieu be.

Trong o dong collector khi co tn hieu ac ch bang 1/10 bien o dongcollector tnh. Trong che o tn hieu ln, bien o nh nh cua tn hieu cothe chiem het bien o ng tai. Trong cac he thong x ly am thanh, tn hieube t au CD c dung nh tn hieu vao cua bo tien khuyech ai. Tienkhuyech ai la mach khuyech ai tn hieu be. ay, tn hieu c khuyechai len bien o thch hp cho tang ieu chnh am sac hoac ieu chnh amlng. Sau o tn hieu c a vao tang khuyech ai cong suat. Khuyech aicong suat la mach khuyech ai tn hieu ln. No tao ra mot cong suat t vaimW en hang tram W e a ra loa.


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VI.3 KHUYECH AI HANG A

Hnh 6-4a la mach khuyech ai VDB hang A vi tn hieu ra khong bcat. Chung ta hay dan ra mot so phng trnh cho mach khuyech ai nay.

HE SO KHUYECH AI CONG SUATChung ta nh ngha he so khuyech ai cong suat la

G= Pout / Pin (6-6)He so khuyech ai cong suat bang ty so cong suat loi ra chia cho cong

suat loi vao.V du mach khuyech ai hnh 6-4a co cong suat ra la 10mW va cong

suat vao 10W th he so khuyech ai cong suat bangG = 10mW / 10W = 1000

CONG SUAT RA

Hnh 6-4

Neu o the ra tren hnh 6-4a bang gia tr hieu dung th cong suat ra cua

mach khuyech ai tren laPout = V2rms / RL (6-7)Neu ky hieu Vout la the ra nh nh th (6-7) tr thanh

Pout = V2out / 8RL (6-8)Cong suat ra cc ai khi Vout = MPP hay

Pout(max) = MPP2/ 8RL (6-9)


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V du: Cho mach tren hnh 6-14. Transistor Darlington co=10000. Tnh tr khang vao va tn hieu ra nh - nh cc ai cuamach.

re = 60//30 = 20Tr khang vao cua Q1 bangzin(base) = 10000(20) =200KDong emitter dc cua Q2 la:IEQ= (10V-1.4V)/ 60 = 143mAThe collector-emitter tnh bangVCEQ=15V- (60.143mA) = 15V 8.6V = 6.4VThe xoay chieu nh tai emitter bangICQ.re = (143mA)(20)= 2.86VMPP =2 VCEQ =2(2.86)=5.72V

VI.9 LAP LAI EMITTER AY KEO HANG B

Khuyech ai hang B co ngha la dong collector ch ton tai trong chu ky cua tn hieu. e ieu nay xay ra, iem Q phai trong vungngng dan. u iem cua khuyech ai hang B la dong cung cap t nguonbe va hieu suat cao.

Hnh 6-15


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Hnh 6-17

Hoat ong tong quat cua mach nh sau:Na chu ky dng transistor pha tren dan, transistor pha di

ngng dan. Transistor pha tren giong nh mot mach lap lai emitterthong thng do o the tren tai bang the vao. Ngc lai, na chu ky amtransistor pha di dan, transistor pha tren ngng dan. Transistor phadi cung giong nh mot mach lap lai emitter thong thng do o thetren tai bang the vao.

ac iem cua mach la co tr khang vao cao neu nh dung cactransistor Darlington.

MEO XUYEN TAM

Hnh 6-18

Neu khong phan cc cho 2 transistor nh mach hnh 6-18, the racua bo khuyech ai se b meo khi tn hieu vao cha vt mc 0.7V.e tranh sai dang ngi ta phan cc nhe cho transistor e iem Q nampha tren vung ngng dan mot chut. Thong thng chon ICQ bang 1 en5% cua IC(sat).


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Cac cong thc sau ay ap dung cho khuyech ai ay keo hang B.G = Pout / Pin (he so khuyech ai cong suat)

pout = v2out / 8RL (cong suat ra ac)

pout(max)= MPP2

/ 8RL (cong suat ra ac toi a)Pdc =VCCIdc (cong suat vao dc)

=(pout / pin). 100% (hieu suat)

CONG SUAT TIEU TAN CUA TRANSISTOR

Ly tng th cong suat tieu tan cua transistor hang B bang 0 vkhong co dong dc. Neu co phan cc chong meo xuyen tam th cong suattieu tan cua transistor cung rat nho.

Khi co tn hieu vao, cong suat tieu tan cua transistor tr nen angke. Cong suat tieu tan cua moi transistor trong khuyech ai ay keohang B co the tnh theo cong thc sau:

PD(max) = MPP2/ 40RL (6-26)

VI.10 PHAN CC KHUYECH AI AY KEO HANG B

Kho khan nhat khi thiet ke mach khuyech ai ay keo hang B laat iem Q gan vung ngng dan. Hnh 6-19a cho thay mach phan ccbang cau chia the. e tranh sai dang xuyen tam ngi ta phan cc nhecho cap transistor vi VBE 0.6V en 0.7V. Nhng co mot kho khan ladong collector rat nhay vi thay oi cua the VBE . So lieu cua transistorcho thay neu VBE tang 60mV th dong collector co the tang 10 lan.Thng ngi ta thay ien tr bang bien tr e chon iem Q phu hp.Nhng no van khong giai quyet c van e nhiet o. iem Q co the

rat tot tai nhiet o phong nhng no se thay oi khi nhiet o thay oi(ieu nay la khong tranh khoi tai tang cong suat). Vi cach phan ccnh hnh 6-19a th gia s nhiet o tang ma the phan cc base khong oi(trong khi VBE giam) se lam tang nhanh chong dong collector, ket quala transistor se b chet do qua nhiet.


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Hnh 6-19

Can phai bu lai the phan cc base cua transistor khi nhiet o thay oi.Giai phap la dung mach diode bu nh hnh 6-19b. Tnh chat cua diodebu phai giong nh diode emitter cua transistor. Neu nhiet o tang 1 0Cth the tren diode bu giam 2mV. Do o mach se co tac dung bu nhieto. Thc te la khi nhiet o tang the phan cc se giam, do o dongcollector cung se giam.

V du: Cho mach khuyech ai ay keo hang B nh hnh 6-20. Tnh dongcollector tnh va hieu suat cc ai cua mach.

Giai: Dong phan cc qua diode bu bang

Ibias = (20V 1.4V)/ 2(3.9K) = 2.38mA

ay chnh la gia tr cua dong collector tnh do hieu ng gngdong ien.

Dong collector bao hoa bang

Ic(sat) = VCEQ / RL = 10V / 10 = 1A


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Chng VIICAC HIEU NG TAN SO CUA MACH KHUYECH AI

VII.1 AP TUYEN TAN SO CUA MOT BO KHUYECH AI

ap tuyen tan so cua mot bo khuyech ai la gian o quan he gia heso khuyech ai va tan so. Trong phan nay chung ta se phan tch ap tuyen tanso cua mot mach khuyech ai ac va dc.

AP TUYEN CUA MACH KHUYECH AI AC

Hnh 7-1

Hnh 7-1 cho thay ap tuyen tan so cua mach khuyech ai ac. giaap tuyen he so khuyech ai co gia tr ln nhat. Noi cach khac mach hoatong bnh thng vung gia cac tan so. Tai tan thap do cac tu noi va tuthong dan khong hoan toan noi tat nen he so khuyech ai the giam. Cang gan0Hz he so A cang giam.

Tai tan so cao he so A cung b suy giam v nhng ly do khac. Changhan, gia cac moi noi cua transistor co cac tu ien ky sinh nh hnh 7-2a.Nhng tu nay tao ra ng thong dan cho tn hieu ac. tan so cao, tr khang

cua cac tu nay u be va chung ngan can hoat ong bnh thng cua transistor.Ket qua la gia tr cua A b suy giam tan so cao. Mot ly do khac lam cho Asuy giam tan so cao la cac tu ky sinh cua cac day noi. Ve nguyen tac motday dan la 1 ban tu. Gia mot day dan va GND hnh thanh mot tu ien ky sinhnh hnh 7-2b.


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THE CHUAN 1VOLTDecibel oi khi cung c dung e o mc the ln hn 1V. Khi o

ngi ta ky hieu la dBV (ch V la viet tat cua Volt).VdBV= 20logV (7-12)V du neu the la 25V thVdBV = 20log25 = 28 dBVCo the tnh ra V neu biet dBV theo phng trnh sau:V = antilog (VdBV/ 20) (7-13)Bang sau cho thay quan he gia the V va VdBV

Voltage VdBV10V -50

100V -401mV -30

10mV -20100mV -10

1V 010V +10

100V +20

VII.3 PHOI HP TR KHANG

Hnh 7-4


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decibel. Ngoai thang o tuyen tnh va thang o logarit ngi ta con dungthang o ban logarit. Thang o ban logarit dung thang o tuyen tnh tren tructung con truc hoanh dung thang o logarit. Chung ta dung thang o ban logarite bieu dien cac quan he nh he so khuyech ai the tren nhieu decade cuatan so.

GIAN O DECIBEL CUA HE SO KHUYECH AI THEHnh 7-7 ch ra ap tuyen tan so cua mot bo khuyech ai ac.

Hnh 7-7

Gian o tng t hnh 7-5, nhng chung ta bieu th he so khuyech aibang decibel theo tan so tren thang logarit. Gian o nh vay goi la gian oBode. Truc tung la thang o tuyen tnh con truc hoanh la thang o logarit.

Theo gian o, he so khuyech ai decibel at gia tr cc ai gia. Taitan so cat he so khuyech ai giam va giam vi toc o 20dB/dec.

Tai tan so cat, he so khuyech ai the bang 0.707. Do o he so khuyechai theo decibel tai tan so cat bang

AdB = 20log0.707 =-3dBGian o Bode hnh 7-7 la gian o Bode ly tng a c ly tng hoa.

Gian o Bode ly tng cho phep ve ap tuyen tan so cua mot bo khuyech ainhanh va de dang.

V du chung ta co gian o Bode ly tng nh hnh 7-8. Chung ta co the

thay cac thong tin sau ay. He so khuyech ai gia la 40dB. Tan so cat la1KHz va 100KHz. o doc cua ac tuyen ben di va tren tan so cat la20dB/dec. Ngoai ra chung ta cung thay rang he so khuyech ai the decibelbang 0dB (A=1) tai tan so 10Hz va 100MHz.


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nh ly Miller cho phep phan tch tu phan hoi thanh 2 tu rieng re nhhnh 7-9b. Trong o

Cin = C(A+1) (7-16)Cout = C(A+1)/ A (7-17)Co the thay rang Cout C nhng Cin ln hn tu phan hoi A+1 lan. Hien

tng nay goi la hieu ng Miller. No c dung e tao ra mot tu ao ln hn tuphan hoi nhieu lan.

Mat khac hieu ng Miller con cho thay rang tu phan hoi tao ra motmach tre (lag circuit) loi vao cua bo khuyech ai. Chnh tu Cin la tu chu yeuquy nh tan so cat thap cua bo khuyech ai.

QUAN HE GIA BANDWIDTH VA THI GIAN TANGXet mach RC au vao cua bo khuyech ai. Ban au tu khong tch

ien nh hnh 7-10a.

Hnh 7-10

Neu ong mach tu se c nap theo ham mu t gia tr 0 en nguon cungcap V. Thi gian tang TR cua mach RC c nh ngha la thi gian ma thetren tu tang t 10% en 90% gia tr cc ai.

De dang tnh cTR =2.2RC (7-18)

Thi gian tang ln hn thi hang RC mot chut.Nh a noi tren, mot bo khuyech ai dc co mot mach tre RC loi vao

ma no lam cho he so khuyech ai the decibel giam 20dB/dec. Tan so cat cuamach RC nay cho bi

f2=1/2RCLu y en phng trnh (7-18) th


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f2=0.35/TR (7-19)Phng trnh (7-19) la quan he gia thi gian tang va band thong cua

mach. Trong mach khuyech ai dc band thong co ngha la tat ca cac tan so t0 en tan so cat. Band thong la cach noi khac cua tan so cat. Chang han noimot mach khuyech ai dc co band thong 100KHz co ngha la tan so cat cuamach cung la 100KHz.

VII.6 PHAN TCH TAN SO CUA BO KHUYECH AI

Chung ta se phan tch ay cac hieu ng tan so cua mot bo khuyechai CE phan cc bang cau chia the.

Tan so cat thap f1 cua bo khuyech ai CE quy nh bi:a)Tu noi vaoKhi mot tn hieu ac c a vao bo khuyech ai, mach tng ng

nh hnh 7-11.

Hnh 7-11

Mach noi co tan so cat bangf1= 1/2RC (7-20)trong o R gom RG va Rin.

b) Tu noi raHnh 7-12a cho thay mach tng ng loi ra cua mot bo khuyech ai.

Ap dung nh ly Thevenin chung ta thu c mach hnh 7-12b.Co the dung (7-20) e tnh tan so cat thap, trong o R bang tong cua RL va RC


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Hnh 7-12

Tan so cat cao f2 cua khuyech ai CE quy nh bi cac tu ky sinh tren collector

Hnh 7-13

Hnh 7-13 cho thay mot mach CE vi tu ky sinh Cstray . Tu Cc la tu giacc C va cc B ben trong transistor. Mac du C stray va Cc rat be nhng tai tanso cao chung se co anh hng.


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Hnh 8-2a cho thay mach phan cc cho JFET.

Hnh 8-2

oi vi JFET, chung ta luon luon phan cc ngc diode cong nguon. Dophan cc ngc, dong cong xap x bang 0. ieu nay co ngha la JFET co ientr vao bang vo cung (thng la hang tram M). ay la u iem cua JFET sovi transistor. o la ly do giai thch v sao JFET la rat tot trong cac ng dungyeu cau tr khang vao cao, chang han bo lap lai nguon (source fllower).

THE GATE IEU KHIEN DONG MANGTren hnh 8-2a, cac electron chay t nguon en mang phai qua kenh

hep gia cac vung ngheo. Khi the phan cc am hn, lp ngheo rong ra vakenh dan cua JFET hep hn. Ro rang la bang cach thay oi the V GS co theieu khien dong ien chay gia nguon va mang.

JFET la thiet b ieu khien bi ien the v the vao ieu khien dong ra.Trong JFET, the VGS quy nh dong mang nguon. Khi VGS bang 0 dong mangla cc ai. Khi VGS u ln hai vung ngheo cham nhau th dong mang bangkhong.

Hnh 8-2b la s o ky hieu cua JFET kenh n v kenh dan gia nguon vamang la ban dan loai n. Trong cac ng dung tan so thap cc mang D va ccnguon G la co the oi cho cho nhau. Nhng trong cac ng dung tan so cao thkhong the trao oi D va G v tu tap tan gia DG va DS la khac nhau ang ke.

Ngoai JFET kenh n con co JFET kenh p. Ky hieu JFET kenh p nhJFET kenh n nhng mui ten hng ngc lai. Hoat ong cua JFET kenh p labo tuc vi JFET kenh n.


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NG CONG MANGHnh 8-3a cho thay mot mach phan cc JFET.

Hnh 8-3

Trong mach nay the VGS bang nguon VGG va the nguon mang VDS bangthe nguon cc mang VDD.

Co nh VGS=0V (bang cach ngan mach cc cong nh hnh 8-3b) vabang cach thay oi the VDS chung ta se thu c ng cong IDS(VDS).

Khi tang VDS t gia tr 0

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