Transistor Lưỡng Cực

TRANSISTOR Lng ccBi:

Khoa CNTT HSP KT Hng Yn

Tng quan

Bi ny s gii thiu v tranzito lng cc (Bipolar Junction Transistor BJT). y llinh kin bn dn quan trng c 2 lp tip xc P-N v 3 chn in cc. Trong bi s trnhby v nguyn l hot ng ca tranzito lng cc 3 ch cp in phn cc cho nl ch tch cc, ch ngt v ch bo ha. Bi ny trnh by v cc cch mc cbn ca tranzito lng cc trong cc s mch khuch i l cch mc cc gc chung,cc pht chung v cc gp chung, c im ca tng cch mc. Trong bi ny cn cp n cc phng php phn cc cho tranzito nh phn cc bng dng cc gc, phncc bng phn p v phn cc bng hi tip. ng thi trong chng ny cng trnh byv cc s tng ng ca tranzito trong ch khuch i tn hiu nh v trnh byv ch chuyn mch ca tranzito.

C s nguyn l

Ch hot ng ca transistor npn v pnp

Tranzito lng cc gm c hai tip xc P-N c to nn bi 3 min bn dn loi P vN xp xen k nhau. Nu min bn dn gia l bn dn loi N th ta c tranzito lngcc loi P-N-P. Nu min bn dn gia l bn dn loi P th ta c tranzito lng ccloi N-P-N.

TRANSISTOR Lng cc

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a. Tranzito lng cc loi P-N-P (hay tranzito thun) cu to v k hiu trn s mch; b.Tranzito N-P-N (hay tranzito ngc) cu to v k hiu.

Tranzito c 3 chn cc l:

- Cc Pht k hiu l ch E (Emitter) l ngun pht ra cc ht ti in trong tranzito.

- Cc Gc k hiu l ch B (Base) l cc iu khin dng in..

- Cc Gp k hiu l ch C (Collector) c nhim v thu nhn tt c cc ht dn t phnpht E qua phn gc B ti.

- Hai tip xc P-N l tip xc pht-gc k hiu l TE (gi tt l tip xc pht), v tipxc gp-gc k hiu l TC (gi tt l tip xc gp).

Nguyn l lm vic ca tranzito

Khi cha cung cp in p ngoi ln cc chn cc ca tranzito th hai tip xc phtTE v gp TC u trng thi cn bng v dng in tng chy qua cc chn cc catranzito bng 0.

Mun cho tranzito lm vic ta phi cung cp cho cc chn cc ca n mt in p mtchiu thch hp. C ba ch lm vic ca tranzito l: ch tch cc (hay ch khuch i), ch ngt v ch dn bo ha. C hai loi tranzito P-N-P v N-P-Nu c nguyn l lm vic ging nhau, ch c chiu ngun in cung cp vo cc chncc l ngc du nhau.

TRANSISTOR Lng cc

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+ Ch ngt: Cung cp ngun in sao cho hai tip xc P-N u phn cc ngc.Tranzito c in tr rt ln v ch c mt dng in rt nh chy qua nn tranzito coinh khng dn in.

+ Ch dn bo ha: Cung cp ngun in sao cho c hai tip xc P-N u phn ccthun. Tranzito c in tr rt nh v dng in qua n l kh ln.

ch ngt v ch dn bo ha, tranzito lm vic nh mt phn t tuyn tnh trongmch in. ch ny tranzito nh mt kha in t v n c s dng trong ccmch xung, cc mch s.

+ Ch tch cc: Ta cp ngun in sao cho tip xc pht TE phn cc thun, v tipxc gp TC phn cc ngc. ch tch cc, tranzito lm vic vi qu trnh bin itn hiu dng in, in p, hay cng sut v n c kh nng to dao ng, khuch itn hiu,... y l ch thng dng ca tranzito trong cc mch in t tng t.

So snh gia Transistor loi Ge v Si

c im ca cc ng c tuyn

H c tuyn vo:

c tuyn vo m t mi quan h gia in p vo v dng in vo nh sau:

UEB = f1(IE) khi UCB = const.

Xt trng hp i vi tranzito lng cc Gecmani loi P-N-P. Khi cc gp h th ctuyn vo chnh l c tuyn Vn-Ampe ca tip xc P-N phn cc thun nn ta c:

IE = I0(e UEB/VT 1)

Ta c ng c tuyn vo m t trong hnh 6.2.

TRANSISTOR Lng cc

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H c tuyn vo ca tranzito gecmani loi P-N-P

Khi UCB 0, c tuyn x dch rt t chng t in p trn cc gp t nh hng ndng in qua tip xc pht.

H c tuyn ra:

c tuyn ra biu th mi quan h gia dng in trn mch cc gp vi in p trnmch cc gp. Ta c mi quan h sau:

IC = f2(UCB) khi IE = cont.

Biu thc tnh dng in trn cc gp IC nh sau:

IC = IE + ICBo

TRANSISTOR Lng cc

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H c tuyn ra ca tranzito gecmani loi P-N-P

Thit lp v n nh im lm vic cho transistor

Xc nh in tr Colector (RC)

Mun tranzito lm vic nh mt phn t tch cc th cc phn t ca tranzito phi thomn iu kin thch hp. nhng tham s ny ca tranzito nh mc trc bit, phthuc rt nhiu vo in p phn cc cc chuyn tip colect v emit. Ni mt cchkhc cc gi tr tham s ph thuc vo im cng tc ca tranzito. Mt cch tng qut,d tranzito c mc mch theo kiu no, mun n lm vic ch khuych i cnc cc iu kin sau:

- Chuyn tip emit baz lun phn cc thun.

- Chuyn tip baz colect lun phn cc ngc.

C th minh ha iu ny qua v d xet tranzito, loi pnp (h.2.33). Nu gi UE, UB, UCln lt l in th ca emit, baz, colect, cn c vo cc iu kin phn cc k trnth gia cc in th ny phi tho mn iu kin:

UE > UB > UC

Hy xt iu kin phn cc cho tng loi mch.

TRANSISTOR Lng cc

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-T mch chung baz vi chiu mi tn l hng dng ca in p v dng in, cth xc nh c cc tnh ca in p v dng in cc cc khi tranzito mc CB nhsau:

UEB = UE UB > 0 IE>0

UCB = UC UB> 0 IC 0 IB 0 IC 0 IB

Mch phn cc c nh

- in tr RB, gi l in tr nh thin, c u t dng ngun EC v cc gc phn cc thun cho tip xc pht - gc.

- in tr RC, gi l ti, c nhim v dn in p t dng ngun EC v cc gp saocho tip xc gp - gc phn cc ngc.

Dng in IC chy t dng ngun EC qua RC v m ngun EC. Dng in IB chy tdng ngun EC qua RB v m ngun EC.

Trn ng ti dc ta chn im lm vic thch hp vi iu kin tn hiu u vo c gitr dng in cc gc khng vt qu gi tr dng in I c tnh theo cng thc sau:

IB = (EC UBE)/RB

Theo cng thc trn, c ngun in ECC l c nh, in p UBE chn bng 0,2V chotranzito gecmani v 0,6V cho tranzito silic nn dng IB l c nh. Trong trng hpmun thay i dng in IB, tc l thay i im lm vic tnh Q th ta thay i tr sin tr RB.

V dng IB chn l mt hng s nn s mch trn (hnh 6.4) c gi l mchphn cc kiu c nh hay mch phn cc nh dng cc gc. Dng IB c gi l dngin nh thin.

n nh ca mch nh thin.

Khi tranzito hot ng, cc tham s ca mch s thay i do nhiu nguyn nhn, cbit l do nhit mi trng thay i. V vy, vic n nh im lm vic Q chnl rt cn thit.

TRANSISTOR Lng cc

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Ta gi thit rng tranzito trong hnh 6.4 c thay bng mt tranzito khc cng loinhng c h s khuch i ln hn nh ch ra trong hnh, v v IB gi khng i tiIB2 bng mch phn cc bn ngoi, s dn n vic im lm vic Q1 phi di chuynn Q2.

im lm vic mi ny c th khng tha mn hon ton. c bit n c th lm chotranzito chuyn sang ch bo ha. Lc ny chng ta phi thay i dng in IB m bo ch lm vic cn thit cho tranzito.

n nh nhit cho tranzito:

Vn quan trng th hai gy nh hng n s phn cc ca tranzito l s thay inhit . Nh ta bit dng in ngc bo ha ICBo ph thuc nhiu vo nhit ,iu ny c th gy kh khn cho vic s dng tranzito. Ngay c khi im lm vic tnh c xc nh vng ch tch cc th do nh hng ca nhit n vn c thchuyn sang ch bo ha. Trong hnh 6.5 ch ra h c tuyn ra ca tranzito 2N708ti nhit +250C v +1000C. Ta thy r rng hu nh n lm vic ch bo ha tinhit +1000C mc d n c phn cc gia vng ch tch cc ti +250C.

H c tuyn ra t0 = +250C (a) v +1000C (b) ca tranzito loi N-P-N 2N708

Phn cc bng cu phn p

S mch cho trn hnh:

TRANSISTOR Lng cc

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S mch nh thin phn p

Trong mch, hai in tr R1 v R2 ni tip nhau v u trc tip gia hai cc ca nguncung cp EC s to nn mch phn p, dng in phn p IP. p chy qua R1 v R2khng ph thuc vo s bin i theo nhit ca cc dng in v in p trn ccchn cc ca tranzito. Do , st p do dng phn p to ra trn R2 cng khng phthuc vo hot ng ca tranzito.

in p trn cc gc chnh l st p trn in tr R2 do dng in phn p to nn, vyta c:

UB = IP.p R2

UB = EC.R2/(R1+R2)

Nu ta thay s mch phn cc hnh 6.6 bng s mch phn cc dng hai nguncung cp mt chiu l UB cho mch cc gc v EC cho mch cc gp nh hnh 6.7th in tr RB l in tr tng ng ca hai in tr R1 v R2 mc song song, ta c:

TRANSISTOR Lng cc

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Mch thay th tng ng vi mch nh thin phn p

Nu xt UB v UBE khng ph thuc vo dng in IC, ta c th tnh o hm cngthc (4.31) theo IC c:

Phn cc bng dng phn hi

Trong s , in tr RB c gi l in tr nh thin hoc in tr hi tip. N dnmt phn in p t mch ra v mch vo phn cc cho tip xc pht TE, v in pphn cc l: UBE = UCE - IB RB .

TRANSISTOR Lng cc

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a- S mch nh thin hi tip m in p b- Phng php hn ch hi tip thnh phn tnhiu xoay chiu

Cc phng php mc transistor

Emitter chung (EC)

Trong s mch gm c cc phn t sau:

+/ EE , EC - Ngun in cung cp mt chiu cho tranzito loi P-N-P.

+/ RB - in tr nh thin

+/ RC - in tr ti

+/ T in C1 v C2 l t lin lc.

Cc cu kin ny c nhim v trong mch in tng t nh s mc cc gc chung.

Nh vy, tn hiu a vo gia cc gc v cc pht, tn hiu c ly ra t gia cc gpv cc pht. Do , cc pht l chn cc chung ca mch vo v mch ra v ta c s

TRANSISTOR Lng cc

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mc cc pht chung. Chiu ca cc thnh phn dng in v in p trn cc chn cccu tranzito c m t hnh 6.9.

Trong s mc pht chung c dng vo l IB, dng ra l IC, in p vo l UBE, inp ra l UCE.

S mch cc E chung

Colector chung (CC)

S mch cc E chung

Mch chung colect c dng nh hnh 6.10, cc colect dung chung cho u vo v ura.

o in p vo, dng vo, dng ra qua xc cc c tuyn tnh c bn ca mchCC dung cc vn k v miliampe k c mc nh hnh 6.9.

TRANSISTOR Lng cc

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c tuyn vo ca mch chung colect (CC) IB= f(UCB) khi in p ra UCE khng ic dng nh hnh 2.31 n c dng khc hn so vi cc c tuyn vo ca hai cch mcEC v BC xt trc y. l v trong kiu mc mch ny in p vo UCB ph thucrt nhiu vo in p ra UCE (khi lm vic ch khuych i in p UCB i vitranzito silic lun gi khong 0.7V, cn tranzito Gecmani vo khong 0.3V trong khi in p UCE bin i trong khong rng ). V d trn hnh 2.31 hy xt trng hpUEC = 2V ti IB = 100mA UCB = UCE UBE = 2V 0.7 V =1,3V

Base chung (BC)

S mch mc cc gc chung m t trong hnh 4-10. Trong s mch c:

+ EE , EC l ngun cung cp mt chiu cho tranzito loi P-N-P trong mch.

+ RE - in tr nh thin cho tranzito. RE c nhim v lm st bt mt phn in pngun EE m bo cho tip xc pht c phn cc thun vi in p phn cc UEB 0,6 V cho tranzito Silic, v UEB 0,2V cho tranzito Gecmani. ng thi tn hiu vos h trn RE a vo tranzito.

+ RC - in tr gnh c nhim v to st p thnh phn dng xoay chiu ca tn hiu a ra mch sau v a in p t m ngun EC ln cc gp m bo cho tip xc gpc phn cc ngc.

+ T in C1 , C2 gi l t lin lc c nhim v dn tn hiu vo mch v dn tn hiu ramch sau.

S mc gc chung cho tranzito loi P-N-P

Cc gc B ca tranzito trong s c ni t. Nh vy, tn hiu a vo gia ccpht v cc gc. Tn hiu ly ra gia cc gp v cc gc nn cc gc B l chn cc

TRANSISTOR Lng cc

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chung ca mch vo v mch ra. - Ta gi l s mc cc gc chung. Trong mch ccc thnh phn dng in v in p sau:

IE gi l dng in trn mch vo.

IC gi l dng in trn mch ra.

UEB gi l in p trn mch vo

UCB gi l in p trn mch ra

Mi quan h gia cc dng in v in p trn cc chn cc c m t thng qua cch c tuyn tnh. C hai h c tuyn chnh l :

H c tuyn vo: UEB = f1(UCB, IE)

H c tuyn ra: IC = f2 (UCB, IE)

TRANSISTOR Lng cc

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TRANSISTOR Lng ccTng quanC s nguyn lCh hot ng ca transistor npn v pnpSo snh gia Transistor loi Ge v Si

c im ca cc ng c tuynThit lp v n nh im lm vic cho transistorXc nh in tr Colector (RC)Phn cc cho transistorPhn cc bng dng c nhPhn cc bng cu phn pPhn cc bng dng phn hi

Cc phng php mc transistorEmitter chung (EC)Colector chung (CC)Base chung (BC)