Gio trnh linh kin in t

Bin tp bi:Trng Vn Tm

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Gio trnh linh kin in t

Bin tp bi:Trng Vn Tm

Cc tc gi:Trng Vn Tm

Phin bn trc tuyn:http://voer.edu.vn/c/749e7bb6

MC LC

1. Thng tin gio trnh in t2. Gio trnh linh kin in t-Li ni u3. Khi nim v c hc nguyn lng4. Phn b in t trong nguyn t theo nng lng5. Di nng lng6. linh ng v dn xut7. Phng php kho st chuyn ng ca ht t bng nng lng8. Th nng trong kim loi9. S phn b ca in t trong kim loi10. Cng ra(Hm cng)11. in th tip xc(Tip th)12. Cht bn dn in thun hay ni bm13. Cht bn dn ngoi lai hay c cht pha14. Dn xut ca cht bn dn15. C ch dn in trong cht bn dn16. Phng trnh lin tc17. Cu to ca ni P-N18. Dng in trong ni P-N khi c phn cc19. nh hng ca nhit ln ni P-N20. Ni tr ca ni P-N21. in dung ca ni P-N22. Cc loi DIODE thng dng23. Cu to cn bn ca BJT24. C ch hot ng ca transistor lng cc25. Transistor trng thi cha phn cc26. Cc cch rp transistor v li dng in27. Dng in r trong transistor28. c tuyn V-I ca transistor29. im iu hnh ng thng ly in mt chiu30. Kiu mu mt chiu ca BJT31. BJT vi tn hiu xoay chiu32. Cu to cn bn ca JFET33. C ch hot ng ca JFET

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34. c tuyn truyn ca JFET35. nh hng ca nhit trn JFET36. Mosfet loi him (depletion mosfet de mosfet)37. Mosfet loi tng (enhancement mosfet e-mosfet)38. Xc nh im iu hnh39. Fet vi tn hiu xoay chiu v mch tng ng vi tn hiu nh40. in dn truyn (transconductance) ca jfet v demosfet41. in dn truyn ca e-mosfet42. Tng tr vo v tng tr ra ca fet43. CMOS tuyn tnh (linear cmos)44. Mosfet cng sut v-mos v d-mos45. SCR (thyristor silicon controlled rectifier)46. TRIAC (triod ac semiconductor switch)47. SCS (silicon controlled switch)48. DIAC49. Ujt (unijunction transistor transistor c ni)50. Diod shockley51. GTO (gate turn off switch)52. PUT (Programmable Unijunction Transistor)53. nh sng54. Quang in tr (photoresistance)55. Quang diod (photodiode)56. Quang transistor (photo transistor)57. Diod pht quang (led-light emitting diode)58. Ni quang59. Khi nim v IC - s kt t trong h thng in t60. Cc loi IC61. S lc v qui trnh ch to mt IC n tinh th62. IC s (IC digital) v IC tng t (ic analog)Tham gia ng gp

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Thng tin gio trnh in t

MN: LINH KIN IN T

1. Thng tin tc gi: H Tn: Trng Vn Tm Sinh nm: 1951 nh (k thut s) C quan cng tc: B mn Vin Thng & K Thut iu Khin

Khoa Cng Ngh Thng Tin v Truyn Thng Trng i Hc Cn Th

a ch Email: tvtam@cit.ctu.edu.vn Phm vi v i tng s dng: Dng tham kho cho cc sinh vin chuyn ngnh in T vin thng, t ng,

k thut iu khin, k thut in, c in t...

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C th dng cho cc trng c cc chuyn ngnh k trn Khng cn kin thc trc khi hc Cha xut bn.

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Gio trnh linh kin in t-Li ni uLinh kin in t l kin thc bc u v cn bn ca ngnh in t.

Gio trnh c bin son t cc bi ging ca tc gi trong nhiu nm qua ti KhoaCng Ngh v Cng Ngh Thng Tin, Trng i hc Cn Th v cc Trung Tm Giodc thng xuyn ng bng sng Cu Long sau qu trnh sa cha v cp nht.

Gio trnh ch yu dng cho sinh vin chuyn ngnh in T Vin Thng v T ngHa. Cc sinh vin khi K thut v nhng ai ham thch in t cng tm thy ynhiu iu b ch.

Gio trnh bao gm 9 chng:

T chng 1 n chng 3: Nhc li mt s kin thc cn bn v vt l vi m, cc mcnng lng v di nng lng trong cu trc ca kim loi v cht bn dn in v dngn nh cha kha kho st cc linh kin in t.

T chng 4 n chng 8: y l i tng chnh ca gio trnh. Trong cc chngny, ta kho st cu to, c ch hot ng v cc c tnh ch yu ca cc linh kin int thng dng. Cc linh kin qu c bit v t thng dng c gii thiu ngn gn mkhng i vo phn gii.

Chng 9: Gii thiu s hnh thnh v pht trin ca vi mch.

Ngi vit chn thnh cm n anh Nguyn Trung Lp, Ging vin chnh ca B mnVin Thng v T ng Ha, Khoa Cng Ngh Thng Tin, Trng i hc Cn Th c k bn tho v cho nhiu kin qu bu.

Cn Th, thng 12 nm 2003

Trng Vn Tm

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Khi nim v c hc nguyn lngTa bit rng vt cht c cu to t nhng nguyn t ( l thnh phn nh nht canguyn t m cn gi nguyn tnh cht ca nguyn t ). Theo m hnh ca nh vt lAnh Rutherford (1871-1937), nguyn t gm c mt nhn mang in tch dng (Protonmang in tch dng v Neutron trung ho v in) v mt s in t (electron) mangin tch m chuyn ng chung quanh nhn v chu tc ng bi lc ht ca nhn.Nguyn t lun lun trung ha in tch, s electron quay chung quanh nhn bng sproton cha trong nhn - in tch ca mt proton bng in tch mt electron nhngtri du). in tch ca mt electron l -1,602.10-19Coulomb, iu ny c ngha l c c 1 Coulomb in tch phi c 6,242.1018 electron. in tch ca in t c tho c trc tip nhng khi lng ca in t khng th o trc tip c. Tuy nhin,ngi ta c th o c t s gia in tch v khi lng (e/m), t suy ra c khilng ca in t l:

mo=9,1.10-31Kg

l khi lng ca in t khi n chuyn ng vi vn tc rt nh so vi vn tc nhsng (c=3.108m/s). Khi vn tc in t tng ln, khi lng ca in t c tnh theocng thc Lorentz-Einstein:

Mi in t chuyn ng trn mt ng trn v chu mt gia tc xuyn tm. Theothuyt in t th khi chuyn ng c gia tc, in t phi pht ra nng lng. S mtnng lng ny lm cho qu o ca in t nh dn v sau mt thi gian ngn, int s ri vo nhn. Nhng trong thc t, cc h thng ny l mt h thng bn theo thigian. Do , gi thuyt ca Rutherford khng ng vng.

Nh vt l hc an Mch Niels Bohr (1885- 1962) b tc bng cc gi thuyt sau:

C nhng qu o t bit, trn in t c th di chuyn m khng pht ra nnglng. Tng ng vi mi qu o c mt mc nng lng nht nh. Ta c mt quo dng.

Khi in t di chuyn t mt qu o tng ng vi mc nng lng w1 sang qu okhc tng ng vi mc nng lng w2 th s c hin tng bc x hay hp thu nnglng. Tn s ca bc x (hay hp thu) ny l:

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Trong , h=6,62.10-34 J.s (hng s Planck).

Trong mi qu o dng, moment ng lng ca in t bng bi s ca

Moment ng lng:

Hnh 1

Vi gi thuyt trn, ngi ta d on c cc mc nng lng ca nguyn t hydrov gii thch c quang ph vch ca Hydro, nhng khng gii thch c i vinhng nguyn t c nhiu in t. Nhn thy s i tnh gia sng v ht, Louis deBroglie (Nh vt l hc Php) cho rng c th lin kt mi ht in khi lng m,chuyn ng vi vn tc v mt bc sng = hmv .

Tng hp tt c gi thuyt trn l mn c hc nguyn lng, kh d c th gii thchc cc hin tng quan st c cp nguyn t.

Phng trnh cn bn ca mn c hc nguyn lng l phng trnh Schrodinger cvit nh sau:

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? l ton t Laplacien

E: nng lng ton phn

U: th nng

(E-U): ng nng

l mt hm s gi l hm s sng. Hm s ny xc nh xc sut tm thy ht introng min khng gian ang kho st.

Trong khi gii phng trnh Schrodinger tm nng lng ca nhng in t trongmt nguyn t duy nht, ngi ta thy rng mi trng thi nng lng ca electron phthuc vo 4 s nguyn gi l 4 s nguyn lng:

S nguyn lng xuyn tm: (S nguyn lng chnh)

Xc nh kch thc ca qu o n=1,2,3,7

S nguyn lng phng v: (S nguyn lng ph)

Xc nh hnh th qu o l=1,2,3,,n-1

S nguyn lng t:

Xc nh phng hng ca qu o ml=0,1, , l

S nguyn lng Spin:

Xc nh chiu quay ca electron ms=+12v -12

Trong mt h thng gm nhiu nguyn t, cc s nguyn lng tun theo nguyn lngoi tr Pauli. Nguyn l ny cho rng: trong mt h thng khng th c 2 trng thinguyn lng ging nhau, ngha l khng th c hai in t c 4 s nguyn lng honton ging nhau.

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Phn b in t trong nguyn t theo nnglngTt c cc nguyn t c cng s ngun lng chnh hp thnh mt tng c tn lK,L,M,N,O,P,Q ng vi n=1,2,3,4,5,6,7.

mi tng, cc in t c cng s l to thnh cc ph tng c tn s,p,d,f tng ng vil=0,1,2,3

Tng K (n=1) c mt ph tng s c ti a 2 in t.

Tng L (n=2) c mt ph tng s c ti a 2 in t v mt ph tng p c ti a 6 in t.

Tng M (n=3) c mt ph tng s (ti a 2 in t), mt ph tng p (ti a 6 in t) vmt ph tng d (ti a 10 in t).

Tng N (n=4) c mt ph tng s (ti a 2 in t), mt ph tng p (ti a 6 in t), mtph tng d (ti a 10 in t) v mt ph tng f (ti a 14 in t).

Nh vy: Tng K c ti a 2 in t.

Tng L c ti a 8 in t.

Tng M c ti a 18 in t.

Tng N c ti a 32 in t.

Cc tng O,P,Q cng c 4 ph tng v cng c ti a 32 in t.

ng vi mi ph tng c mt mc nng lng v cc mc nng lng c xp theoth t nh sau:

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Hnh 2

Khi khng b kch thch, cc trng thi nng lng nh b in t chim trc (gn nhnhn) khi ht ch mi sang mc cao hn (xa nhn hn). Th d: nguyn t Na c s int z=11, c cc ph tng 1s,2s,2p b cc in t chim hon ton nhng ch c 1 in tchim ph tng 3s.

Cch biu din:

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Hnh 3

Lp bo ha: Mt ph tng bo ha khi c s in t ti a.

Mt tng bo ha khi mi ph tng bo ha. Mt tng bo ha rt bn, khng nhnthm v cng kh mt in t.

Tng ngoi cng: Trong mt nguyn t, tng ngoi cng khng bao gi cha qu 8 int. Nguyn t c 8 in t tng ngoi cng u bn vng (trng hp cc kh tr).

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Cc in t tng ngoi cng quyt nh hu ht tnh cht ha hc ca mt nguyn t.

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Di nng lngNhng cng trnh kho cu tia X chng t rng hu ht cc cht bn dn u dngkt tinh.

Ta xt mt mng tinh th gm N nguyn t thuc nhm 4A, th d C6. Ta tng tngrng c th thay i c khong cch gia cc nguyn t m khng thay i cu tocn bn ca tinh th. Nu cc nguyn t cch nhau mt khong d1 sao cho tc ng lnnhau khng ng k th cc mc nng lng ca chng trng vi cc mc nng lngca mt nguyn t c nht. Hai ph tng ngoi cng c 2 in t s v 2 in t p(C6=1s22s22p2). Do , nu ta khng n cc tng trong, ta c 2N in t chimtt c 2N trng thi s v c cng mc nng lng; Ta cng c 2N in t p chim 2Ntrng thi p. Vy c 4N trng thi p cha b chim. Gi s khong cch gia cc nguynt c thu nh hn thnh d2, tc dng ca mt nguyn t bt k ln cc nguyn t lncn tr thnh quan trng.

Hnh 4

Ta c mt h thng gm N nguyn t, do cc nguyn t phi tun theo nguyn lPauli. 2N in t s khng th c cng mc nng lng m phi c 2N mc nng lngkhc nhau; khong cch gia hai mc nng kng rt nh nhng v N rt ln nn khongcch gia mc nng lng cao nht v thp nht kh ln, ta c mt di nng lng. 2Ntrng thi ca di nng lng ny u b 2N in t chim. Tng t, bn trn di nnglng ny ta c mt di gm 6N trng thi p nhng ch c 2N trng thi p b chim ch.

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Ta rng, gia hai di nng lng m in t chim-c c mt di cm. in tkhng th c nng lng nm trong di cm, khong cch (di cm) cng thu hp khikhong cch d cng nh (xem hnh). Khi khong cch d=d3, cc di nng lng chngln nhau, 6N trng thi ca di trn ho vi 2N trng thi ca di di cho ta 8N trngthi, nhng ch c 4N trng thi b chim. khong cch ny, mi nguyn t c 4 int tng ngoi nhng ta khng th phn bit c in t no l in t s v in t nol in t p, khong cch t , tc dng ca cc nguyn t ln nhau rt mnh. Sphn b cc di nng lng tu thuc vo dng tinh th v nguyn t s. Ngi ta xcnh s phn b ny bng cch gii phng trnh Schrodinger v c kt qu nh hnh v.Ta c mt di ho tr (valence band) gm 4N trng thi hon ton b chim v mt didn in (conduction band) gm 4N trng thi cha b chim. Gia hai di nng lngny, c mt di nng lng cm c nng lng khong 6eV. (eV: ElectronVolt)

1 volt l hiu in th gia hai im ca mt mch in khi nng lng cung cp l 1Joule chuyn mt in tch 1 Coloumb t im ny n im kia.

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Hnh 5

* Ta c 3 trng hp:

Di cm c cao kh ln (EG>5eV). y l trng hp ca cc cht cch in. Th dnh kim cng c EG=7eV, SiO2 EG=9eV.

Di cm c cao nh (EG

Hnh 6

Gi s ta tng nhit ca tinh th, nh s cung cp nhit nng, in t trong di hatr tng nng lng. Trong trng hp (a), v EG ln, in t khng nng lng vtdi cm vo di dn in. Nu ta cho tc dng mt in trng vo tinh th, v ttc cc trng thi trong di ha tr iu b chim nn in t ch c th di chuyn bngcch i ch cho nhau. Do , s in t i, v mt chiu bng vi s in t i, v theochiu ngc li, dng in trung bnh trit tiu. Ta c cht cch in.

Trong trng hp (b), mt s in t c nng lng s vt di cm vo di dnin. Di tc dng ca in trng, cc in t ny c th thay i nng lng d dngv trong di dn in c nhiu mc nng lng trng tip nhn chng. Vy in t cnng lng trong di dn in c th di chuyn theo mt chiu duy nht di tc dngca in trng, ta c cht bn dn in.

Trong trng hp (c) cng ging nh trng hp (b) nhng s in t trong di dnin nhiu hn lm cho s di chuyn mnh hn, ta c kim loi hay cht dn in.

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linh ng v dn xutTrong chng I, hnh nh ca di nng lng trong kim loi c trnh by. Theo skho st trn, di nng lng do in t chim c th cha y v khng c di cm chonhng nng lng cao. Ngha l in t c th di chuyn t do trong kim loi di tcdng ca in trng.

Hnh trn v phn b in tch trong tinh th Na. Nhng ch gch cho tiu biu chonhng in t di ha tr c nng lng thp nht, nhng ch trng cha nhng int c nng lng cao nm trong di dn in. Chnh nhng in t ny l nhng in tkhng th ni thuc hn vo mt nguyn t nht nh no v c th di chuyn t do tnguyn t ny sang nguyn t khc. Vy kim loi c coi l ni cc ion kt hp chtch vi nhau v xp u n trong 3 chiu trong mt m my in t m trong int c th di chuyn t do.

Hnh nh ny l s m t kim loi trong cht kh in t. Theo thuyt cht kh in tkim loi, in t chuyn ng lin tc vi chiu chuyn ng bin i mi ln va chmvi ion dng nng, c xem nh ng yn. Khong cch trung bnh gia hai ln vachm c gi l on ng t do trung bnh. V y l chuyn ng tn lon, nn mt thi im no , s in t trung bnh qua mt n v din tch theo bt c chiuno s bng s in t qua n v din tch y theo chiu ngc li. Nh vy , dng intrung bnh trit tiu.

Gi s, mt in trng E c thit lp trong mng tinh th kim loi, ta th kho stchuyn ng ca mt in t trong t trng ny.

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Hnh trn m t chuyn ng ca in t di tcdng ca in trng E . Qu oca in t l mt ng gp khc v in t chm vo cc ion dng v i hngchuyn ng. Trong thi gian t=n ln thi gian t do trung bnh, in t di chuyn cmt on ng l x. Vn tc

gi l vn tc trung bnh. Vn tc ny t l vi in trng E . v = E

Hng s t l gi l linh ng ca in t, tnh bng m2/Vsec.

in tch i qua mi n v din tch trong mt n v thi gian c gi l mt dngin J.

Ta c: J = n.e.v

Trong , n: mt in t, e: in tch ca mt electron

V

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gi l in tr sut ca kim loi

in tr sut tnh bng ?m v dn sut tnh bng mho/m

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Phng php kho st chuyn ng ca htt bng nng lng

Phng php kho st ny cn c trn nh lut bo ton lng. d hiu, ta xt th dsau y:

Mt diode l tng gm hai mt phng song song bng kim loi cch nhau 5 Cm. AnodA c hiu in th l 10V so vi Catod K. Mt in t ri Catod K vi nng lng banu Ec=2eV. Tnh khong cch ti a m in t c th ri Catod.

Gi s, in t di chuyn ti im M c honh l x. in th ti im M s t l vihonh x v in trng gia Anod v Catod u.

in th ti mt im c honh x l:

Khi x=0, (ti Catod) V = 0 = 0

Nn

Ti x=5 Cm (ti Anod A) th V=-10volt

Vy V=-2x (volt) vi x tnh bng Cm

Suy ra th nng ti im M l:

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U = QV=+2.e.x(Joule)vi e l in tch ca in t.

Ta c th vit U = 2.x(eV)

Nng lng ton phn ti im M l:

T = 12mv2 + U

Nng lng ny khng thay i. Trn th, T c biu din bng ng thng songsong vi trc x.

Ti im M (x=x0) ta c:

T-U=0

M T=+Ec (nng lng ban u)

T=2.e.V

Vy, U=2.x0 (eV)

=> 2-2.x0=0 => x0=1Cm

V phng din nng lng, ta c th ni rng vi nng lng ton phn c sn T, int khng th vt qua ro th nng U vo phn c gch cho.

Ta thy rng nu bit nng lng ton phn ca ht in v s phn b th nng trongmi trng ht in, ta c th xc nh c ng di chuyn ca ht in.

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Phn sau y, ta p dng phng php trn kho st s chuyn ng ca in t trongkim loi.

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Th nng trong kim loiNu ta c mt nguyn t duy nht th in th ti mt im cch mt khong r l:

V = kr + C

Nu chn in th ti mt im rt xa lm in th Zero th C=0. Vy mt in t cin tch e cch ht nhn mt on r s c th nng l:

Hnh trn l th ca th nng U theo khong cch r. Phn th khng lin tc ngvi mt in t bn tri nhn . Nu ta c hai nhn v th trong vng gia hai nhnny th nng ca in t l tng cc th nng do v to ra. Trong kim loi, cc nhnc sp xp u n theo 3 chiu. Vy, ta c th kho st s phn b ca th nng bngcch xt s phn b dc t, heo di v y..

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Hnh trn biu din s phn b .

Ta thy rng c nhng vng ng th rng nm xen k vi nhng vng in th thayi rt nhanh. Mt ngoi ca mi kim loi khng c xc nh hon ton v cch nhncui cng mt khong cch nh. V bn phi ca nhn khng cn nhn nn th nngtin ti Zero ch khng gi tnh tun hon nh bn trong kim loi. Do , ta c mt roth nng ti mt ngoi ca kim loi.

Ta xt mt in t ca nhn v c nng lng nh hn U0, in t ny ch c thdi chuyn trong mt vng nh cnh nhn gia hai ro th nng tng ng. l int buc v khng tham gia vo s dn in ca kim loi. Tri li, mt in t c nnglng ln hn U0 c th di chuyn t nguyn t ny qua nguyn t khc trong khi kimloi nhng khng th vt ra ngoi khi kim loi c v khi n mt phn cch, int ng vo ro th nng. Cc in t c nng lng ln hn U0 c gi l cc in tt do. Trong cc chng sau, ta t bit ch n cc in t ny.

V hu ht khi kim loi u c cng in th V0 tng ng vi th nng U0=-eV0 nnta c th gi s khi kim loi l mt khi ng th V0. Nhng in th ty thuc vomt hng s cng nn ta c th chn V0 lm in th gc (V0=0V). Gi EB l chiu caoca ro th nng gia bn trong v bn ngoi kim loi. Mt in t bn trong khi kim

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loi mun vt ra ngoi phi c t nht mt nng lng U=EB, v vy ta cn phi bit sphn b ca in t theo nng lng.

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S phn b ca in t trong kim loiGi nE= l s in t trong mt n v th tch c nng lng t E n E+E. Theonh ngha, mt in t trung bnh c nng lng t E n E+E l t s

. Gii hn ca t s ny khi

gi l mt in t c nng lng E.

Do , nu ta bit c hm s (E)ta c th suy ra c s in t c nng lng trongkhong t E n E+dE bng biu thc (2). Ta thy rng (E) chnh l s trng thi nnglng E b in t chim. Nu gi n(E) l s trng thi nng lng c nng lng Em in t c th chim c. Ngi ta chng minh c rng: t s (E)n(E) bng mt hms f(E), c dng:

Trong , K=1,381.10-23 J/0K (hng s Boltzman)

K = 1,381.1023

e = 8,62.10 5(V/0K)

EF nng lng Fermi, ty thuc vo bn cht kim loi.

Mc nng lng ny nm trong di cm.

nhit rt thp (T00K)

Nu EEF, ta c f(E)=0

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Vy f(E) chnh l xc sut tm thy in t c nng lng E nhit T.

Hnh trn l th ca (E) theo E tng ng vi nhit T=00K v T=2.5000K.

Ta thy rng hm (E) bin i rt t theo nhit v ch bin i trong vng cn canng lng EF. Do , nhit cao (T=2.5000K) c mt s rt t in t c nng lngln hn EF, hu ht cc in t u c nng lng nh hn EF. Din tch gii hn bing biu din ca (E) v trc E cho ta s in t t do n cha trong mt n v thtch.

( l f(E)=1 v T=00K)

T y ta suy ra nng lng Fermi EF

Nu ta dng n v th tch l m3 v n v nng lng l eV th ? c tr s l:

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y= 6,8.1027

Do ,

Nu bit c khi lng ring ca kim loi v s in t t do m mi nguyn t cth nh ra, ta tnh c n v t suy ra EF. Thng thng EF < 10eV.

Th d, khi lng ring ca Tungsten l d = 18,8g/cm3, nguyn t khi l A = 184, bitrng mi nguyn t cho v = 2 in t t do. Tnh nng lng Fermi.

Gii: Khi lng mi cm3 l d, vy trong mt cm3 ta c mt s nguyn t khi l d/A.Vy trong mi cm3, ta c s nguyn t thc l:

dA .A0 vi A0 l s Avogadro (A0 = 6,023.10

23)

Mi nguyn t cho v = 2 in t t do, do s in t t do trong mi m3 l:

n = dA .A0.v.106

Vi Tungsten, ta c:

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Cng ra(Hm cng)Ta thy rng nhit thp (T 00K), nng lng ti a ca in t l EF (E

in th tip xc(Tip th)

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Cht bn dn in thun hay ni bm

Khi nng lng ny ln hn nng lng ca di cm (0,7eV i vi Ge v 1,12eV ivi Si), in t c th vt di cm vo di dn in v cha li nhng l trng (trngthi nng lng trng) trong di ha tr). Ta nhn thy s in t trong di dn in bngs l trng trong di ha tr.

Nu ta gi n l mt in t c nng lng trong di dn in v p l mt l trngc nng lng trong di ha tr. Ta c:n=p=ni

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Ngi ta chng minh c rng:

ni2 = A0.T3. exp(-EG/KT)

Trong : A0 : S Avogadro=6,203.1023

T : Nhit tuyt i ( Kelvin)

K : Hng s Bolzman=8,62.10-5 eV/0K

EG : Chiu cao ca di cm.

Ta gi cht bn dn c tnh cht n=p l cht bn dn ni bm hay cht bn dn thun.Thng thng ngi ta gp nhiu kh khn ch to cht bn dn loi ny.

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Cht bn dn ngoi lai hay c cht phaCht bn dn loi N: (N - type semiconductor)

Gi s ta pha vo Si thun nhng nguyn t thuc nhm V ca bng phn loi tun honnh As (Arsenic), Photpho (p), Antimony (Sb). Bn knh nguyn t ca As gn bngbn knh nguyn t ca Si nn c th thay th mt nguyn t Si trong mng tinh th.Bn in t ca As kt hp vi 4 in t ca Si ln cn to thnh 4 ni ha tr, Cn dli mt in t ca As. nhit thp, tt c cc in t ca cc ni ha tr u c nnglng trong di ha tr, tr nhng in t tha ca As khng to ni ha tr c nnglng ED nm trong di cm v cch dy dn in mt khang nng lng nh chng0,05eV.

Gi s ta tng nhit ca tinh th, mt s ni ha tr b gy, ta c nhng l trng trongdi ha tr v nhng in t trong di dn in ging nh trong trng hp ca cc chtbn dn thun. Ngoi ra, cc in t ca As c nng lng ED cng nhn nhit nng tr thnh nhng in t c nng lng trong di dn in. V th ta c th coi nh huht cc nguyn t As u b Ion ha (v khang nng lng gia ED v di dn in rtnh), ngha l tt c cc in t lc u c nng lng ED u c tng nng lng tr thnh in t t do.

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Nu ta gi ND l mt nhng nguyn t As pha vo (cn gi l nhng nguyn t chodonor atom).

Ta c: n = p + ND

Vi n: mt in t trong di dn in.

P: mt l trng trong di ha tr.

Ngi ta cng chng minh c: n.p = ni2 (n

nhit thp (T=00K), tt c cc in t u c nng lng trong di ha tr. Nu tatng nhit ca tinh th s c mt s in t trong di ha tr nhn nng lng v vtdi cm vo di dn in, ng thi cng c nhng in t vt di cm ln chim chnhng l trng c nng lng EA.

Nu ta gi NA l mt nhng nguyn t In pha vo (cn c gi l nguyn t nhn),ta cng c:

p = n + NA

p: mt l trng trong di ha tr.

n: mt in t trong di dn in.

Ngi ta cng chng minh c:

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n.p = ni2 (p>n)

ni l mt in t hoc l trng trong cht bn dn thun trc khi pha.

Cht bn dn nh trn c s l trng trong di ha tr nhiu hn s in t trong di dnin c gi l cht bn dn loi P.

Nh vy, trong cht bn dn loi p, ht ti in a s l l trng v ht ti in thiu sl in t.

Cht bn dn hn hp:

Trong trng hp cht bn dn hn hp, ta c:

n+NA = p+ND

n.p = ni2

Nu ND > NA => n>p, ta c cht bn dn hn hp loi N.

Nu ND < NA => n

Dn xut ca cht bn dnDi tc dng ca in trung, nhng in t c nng lng trong di dn in dichuyn to nn dng in In, nhng cng c nhng in t di chuyn t mt ni ha trb gy n chim ch trng ca mt ni ha tr b gy. Nhng in t ny cng to ramt dng in tng ng vi dng in do l trng mang in tch dng di chuynngc chiu, ta gi dng in ny l Ip. Hnh sau y m t s di chuyn ca in t(hay l trng) trong di ha tr nhit cao.

Vy ta c th coi nh dng in trong cht bn dn l s hp thnh ca dng in donhng in t trong di dn in (a s i vi cht bn dn loi N v thiu s i vicht bn dn loi P) v nhng l trng trong di ha tr (a s i vi cht bn dn loiP v thiu s i vi cht bn dn loi N).

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Tng ng vi nhng dng in ny, ta c nhng mt dng in J, Jn, Jp sao cho: J= Jn+Jp

Ta chng minh c trong kim loi:

J = n.e.v = n.e..E

Tng t, trong cht bn dn, ta cng c:

Jn=n.e.vn=n.e. n.E (Mt dng in tri ca in t, n l linh ng ca in t, nl mt in t trong di dn in)

Jp=p.e.vp=p.e.p.E (Mt dng in tri ca l trng, p l linh ng ca l trng,p l mt l trng trong di ha tr)

Nh vy: J=e.(n.n+p.p).E

Theo nh lut Ohm, ta c:

J = .E

=> = e.(n.n+p.p) c gi l dn sut ca cht bn dn.

Trong cht bn dn loi N, ta c n>>p nn n = n.n.e

Trong cht bn dn loi P, ta c p>>n nn p = n.p.e

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C ch dn in trong cht bn dnDi tc dng ca in trng, cc in t v l trng di chuyn vi vn tc trung bnhvn=n.E v vp=p.E.

S in t v l trng di chuyn thay i theo mi thi im, v ti mi thi im cmt s in t v l trng c sinh ra di tc dng ca nhit nng. S in t sinh ratrong mi n v thi gian gi l tc sinh to g. Nhng in t ny c i sng trungbnh n v trong khi di chuyn in t c th gp mt l trng c cng nng lng v tihp vi l trng ny. Nu gi n l mt in t, trong mt n v thi gian s in tb mt i v s ti hp l n/n. Ngoi ra, trong cht bn dn, s phn b ca mt int v l trng c th khng u, do

Dng in khuch tn ca in t i qua A l:

Dn c gi l hng s khuch tn ca in t.

Suy ra mt dng in khuch tn ca in t l:

Tng t, trong mt giy c

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l trng b mt i, vi p l mt l trng v p l l i sng trung bnh ca l trng.

Dng in khuch tn ca l trng trong mu bn dn trn l:

V mt dng in khuch tn ca l trng l:

Ngi ta chng minh c rng:

Vi: K l hng s Boltzman = 1,382.10-23J/0K

T l nhit tuyt i.

H thc ny c gi l h thc Einstein.

nhit bnh thng (3000K): VT=0,026V=26mV

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Phng trnh lin tcXt mt hnh hp c tit din A, chiu di dx t trong mt mu bn dn c dng inl trng Ip i qua. Ti mt im c honh x, cng dng in l Ip. Ti mt chonh l x+dx, cng dng in l Ip+dIp. Gi P l mt l trng trong hnhhp, p l i sng trung bnh ca l trng. Trong mi giy c

l trng b mt i do s ti hp. Vy mi giy, in tch bn trong hp gim i mtlng l:

(do ti hp)

ng thi in tch trong hp cng mt i mt lng:

G2=dIp (do khuch tn).

Gi g l mt l trng c sinh ra do tc dng nhit, trong mi giy, in tch tronghp tng ln mt lng l:

T1=e.A.dx.g

Vy in tch trong hp bin thin mt lng l:

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bin thin bng:

Vy ta c phng trnh:

(1)

Nu mu bn dn trng thi cn bng nhit v khng c dng in i qua, ta c:

dIp=0; P=P0=hng s

Phng trnh (1) cho ta:

Vi P0 l mt l trng trng thi cn bng nhit. Thay tr s ca g vo phng trnh(1) v rng p v IP vn ty thuc vo thi gian v khong cch x, phng trnh (1)tr thnh:

(2)

Gi l phng trnh lin tc.

Tng t vi dng in t In, ta c:

(3)

TD: ta gii phng trnh lin tc trong trng hp p khng ph thuc vo thi gian vdng in Ip l dng in khuch tn ca l trng:

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Cu to ca ni P-NHnh sau y m t mt ni P-N phng ch to bng k thut Epitaxi:

Trc tin, ngi ta dng mt thn Si-n+ (ngha l pha kh nhiu nguyn t cho). Trnthn ny, ngi ta ph mt lp cch in SiO2 v mt lp verni nhy sng. Xong ngita t ln lp verni mt mt n c l trng ri dng mt bc x chiu ln mt n,vng verni b chiu c th ra c bng mt loi axid v cha ra mt phn Si-n+, phncn livn c ph verni. Xuyn qua phn khng ph verni, ngi ta cho khuch tnnhng nguyn t nhn vo thn Si-n+ bin mt vng ca thn ny thnh Si-p. Saucng, ngi ta ph kim loi ln cc vng p v n+ v hn dy ni ra ngoi. Ta c mtni P-N c mt ni gia vng p v n+ thng.

Khi ni PN c thnh lp, cc l trng trong vng P khuch tn sang vng N v ngcli, cc in t trong vng N khuch tn sang vng P. Trong khi di chuyn, cc in tv l trng c th ti hp vi nhau. Do , c s xut hin ca mt vng hai bn mini trong ch c nhng ion m ca nhng nguyn t nhn trong vng P v nhng iondng ca nguyn t cho trong vng N. cc ion dng v m ny to ra mt in trngEj chng li s khuch tn ca cc ht in, ngha l in trng Ei s to ra mt dngin tri ngc chiu vi dng in khuch tn sao cho dng in trung bnh tng hptrit tiu. Lc , ta c trng thi cn bng nhit. Trn phng din thng k, ta c thcoi vng c nhng ion c nh l vng khng c ht in di chuyn (khng c in t

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t do vng N v l trng vng P). Ta gi vng ny l vng khim khuyt hay vnghim (Depletion region). Tng ng vi in trng Ei, ta c mt in th V0 hai bnmt ni, V0 c gi l ro in th.

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Ly tch phn 2 v t x1 n x2 v rng ti x1 in th c chn l 0volt, mt l trng l mt Ppo vng P lc cn bng. Ti x2, in th l V0 v mt l trngl Pno vng N lc cn bng.

M:

Nn: V0 = VTlog(PPoPno )Hoc: V0 = KTe log(NDNAni2 )

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Tng t nh trn, ta cng c th tm V0 t dng in khuch tn ca in t v dngin tri ca in t.

Thng thng

nu ni P-N l Si

volt nu ni P-N l Ge

Vi cc hp cht ca Gallium nh GaAs (Gallium Arsenide), GaP (Gallium Phospho),GaAsP (Gallium Arsenide Phospho), V0 thay i t 1,2 volt n 1,8 volt. Thng ngita ly tr trung bnh l 1,6 volt.

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Dng in trong ni P-N khi c phn ccTa c th phn cc ni P-N theo hai cch:

- Tc dng mt hiu in th gia hai cc ca ni sao cho in th vng P ln hn vngN mt tr s V. Trng hp ny ta ni ni P-N c phn cc thun (Forward Bias).

- Nu in th vng N ln hn in th vng P, ta ni ni P-N c phn cc nghch(Reverse Bias).

Ni P-N c phn cc thun:

Khi cha c phn cc, ngang mi ni ta c mt ro in th V0. Khi phn cc thunbng hiu in th V th ro in th gim mt lng V v tr thnh VB = V0-V, do ni P-N mt thng bng. L trng khuch tn t vng P sang vng N to ra dng inIp. in t khuch tn t vng N sang vng P to ra dng in In. Dng in I qua niP-N l : I = Ip + In

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Dng in I khng ph thuc vo thi gian v v tr ca tit din A v ta c mt trngthi thng xuyn nhng dng in In v Ip ph thuc vo v tr ca tit din.

Trong vng P xa vng him, l trng tri di tc dng ca in trng to nn dngJpp. Khi cc l trng ny n gn vng him, mt s b ti hp vi cc in t t vngN khuch tn sang. V vng him rt mng v khng c in t nn trong vng ny ccl trng khuch tn thng ngang qua m khng b mt v tip tc khuch tn sang vngN nhng b mt ln v c s ti hp vi cc in t trong vng ny.

Tng t, s khuch tn ca in t t vng N sang vng P cng tun theo qui ch trn.Ta l cc th nhn mt trc i xng v tng s cc dng in l trng v dngin t phi bng mt hng s.

Ta c: Jpp (x1) = Jpn(x2)

Jnp (x1) = Jnn(x2)

Dng in J ti mt tit din bt k l hng s. Vy ti x1 hoc x2 ta c:

J = Jpp(x1) + Jnp (x1) = Jpn(x2) + Jnn(x2)

Dng in Jpn l dng khuch tn cc l trng, nn c tr s ti tit din x l:

Jpn(x) = e.Dp.dPn(x)

dx

Trong , Pn(x) l mt l trng trong vng N ti im x. Ta tnh Pn(x)

Ta dng phng trnh lin tc:

V dng in Jpn khng ph thuc vo thi gian nn phng trnh tr thnh:

Trong

V c nghim s l:

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Suy ra,

Ta chp nhn khi c dng in qua mi ni, ta vn c biu thc: dv = VT dpp nh trongtrng hp ni cn bng.

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T l nhit tuyt i.

nhit bnh thng, T=2730K, VT=0,026 volt. Khi mi ni chuyn vn bnh thng,V thay i t 0,3 V n 0,7 V ty theo mi l Ge hay Si,

Vy,

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Ghi ch: Cng thc trn ch ng trong trng hp dng in qua mi ni kh ln (vngc tuyn V-I thng, xem phn sau); vi dng in I tng i nh (vi mA tr xung),ngi ta chng minh c dng in qua mi ni l:

Vi ? = 1 khi mi ni l Ge

? = 2 khi mi ni l Si

Ni P-N khi c phn cc nghch:

Khi ni P-N c phn cc nghch, ro in th tng mt lng V. L trng v in tkhng th khuch tn ngang qua mi ni. Tuy nhin, di tc dng ca nhit, mt s tin t v l trng c sinh ra trong vng him to ra mt dng in c chiu t vngN sang vng P. V in t v l trng sinh ra t nn dng in ngc rt nh, thngchng vi chc A hay nh hn. l dng in ngc ny l mt hm s ca nhit.

Ngi ta cng chng minh c trong trng hp ni P-N phn cc nghch vi hiuin th V

I0 cng c tr s:

Thng thng, eV

VT

Khi hiu th phn cc thun cn nh, dng in I tng chm. Khi hiu th phn ccthun ln, dng in I tng nhanh trong lc hiu in th hai u mi ni tng rt t.

Khi hiu th phn cc nghch cn nh, ch c 1 dng in r I0 chy qua. Khi hiu inth phn cc nghch ln, nhng ht ti in sinh ra di tc dng ca nhit c intrng trong vng him tng vn tc v c nng lng rt nhiu in t khc t ccni ha tr. C ch ny c chng cht, sau cng ta c mt dng in ngc rt ln, tani ni P-N trung vng ph hy theo hin tng tuyt (avalanche).

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nh hng ca nhit ln ni P-NDng in bo ha ngc I0 ty thuc vo nng cht pha,din tch mini v nht l nhit .

Thng thng ta thy rng I0 s tng ln gp i khi nhit mi ni tng ln 100C

vi t l nhit (0C)

Hnh sau y m t s bin thin ca dng in bo ha ngc theo nhit .

Th d: 1N914B l diode Si chuyn mch nhanh c dng bo ha ngc I0=25nA 250C. Tm I0 1000C.

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Tnh cht ca ni P-N khi phn cc thun cng thay i theo nhit .

Nhit ca ni P-N cng quyt nh in th sp .

Nu nhit tng ln n mt tr no th in th sp s gim xung rt nh vmi ni P-N khng cn s dng c na. Nhit ny l 1500C i vi Si v 850Ci vi Ge.

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Ni tr ca ni P-NNgi ta thng ch n hai loi ni tr ca ni P-N

Ni tr tnh: (Static resistance).

Ni tr tnh l in tr ni ca ni P-N trong mch in mt chiu. Ngi ta nh nghain tr mt chiu mt im phn cc l t s V/I im .

Ni tr ca ni ti im Q l:

RD =VI

Khi ni P-N phn cc thun cng mnh, dng in I cng ln trong lc in th V gnnh khng i nn ni tr cng nh.

Ni tr ng ca ni P-N: (Dynamic Resistance)

Khi V bin thin mt lng V t tr s VQ th I cng bin thin mt lng tng ngI t tr s IQ. T s

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bng vi dc ca tip tuyn ti im Q vi c tuyn ca ni P-N.

nhit bnh thng (250C), VT = 26mV, in tr ng l:

Vi dng in I kh ln, ?=1, in tr ng rd c th c tnh theo cng thc:

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nhit bnh thng, nu IQ = 100mA th rd = 0,26?. Trong mt ni P-N thc, v ctip tr gia cc mi ni, in tr gia hai vng bn dn P v N nn in tr ng thcs ln hn nhiu so vi tr s tnh c, thng thng khong vi chc ?.

y cng chnh l kiu mu ca Diode vi tn hiu nh. Ngi ta cng nh ngha intr ng khi phn cc nghch

V dc ca tip tuyn ti Q khi ni P-N phn cc nghch rt nh nn in tr ng rrrt ln, hng M?.

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in dung ca ni P-Nin dung chuyn tip (in dung ni)

Khi ni P-N c phn cc nghch, vng him c ni rng do c s gia tng in tchtrong vng ny. Vi mt s bin thin V ca hiu in th phn cc nghch, in tchtrong vng him tng mt lng Q. Vng him c tc dng nh mt t in gi l indung chuyn tip CT.

Trong , l hng s in mi ca cht bn dn, A l in tch ca ni P-N v Wd l rng ca vng him.

Khi in th phn cc nghch thay i, rng ca vng him thay i nn in dungchuyn tip CT cng thay i. Ngi ta chng minh c CT c tr s:

Trong , K l hng s ty thuc vo cht bn dn v k thut ch to. V0 l ro inth ca ni P-N (Si l 0,7V v Ge l 0,3V). VR l in th phn cc nghch. n = 13 trongtrng hp ni P-N l dc li (linearly graded juntion) v n = 12 trong trng hp ni P-Nthuc loi dc ng (brupt juntion).

Nu gi Cj(0) l tr s ca CT o c khi VR=0, ta c:

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Trong cc ni P-N thng thng, CT c tr s t 5pF n 100pF

in dung khuch tn. (Difusion capacitance)

Khi ni P-N c phn cc thun, l trng c khuch tn t vng P sang vng N vin t khuch tn t vng N sang vng P. S phn b cc ht ti in thiu s haibn vng him to nn mt in dung gi l in dung khuch tn CD.. Ngi ta chngminh c in dung khuch tn CDt l vi dng in qua ni P-N theo cng thc:

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Cc loi DIODE thng dngDiode c bn l mt ni P-N. Th nhng, ty theo mt cht tp pha vo cht bn dnthun ban u, ty theo s phn cc ca diode v mt s yu t khc na m ta c nhiuloi diode khc nhau v tm ng dng ca chng cng khc nhau.

Diode chnh lu:

L diode thng dng nht, dng i in xoay chiu thng l in th 50Hz n60Hz sang in th mt chiu. Diode ny ty loi c th chu ng c dng t vitrm mA n loi cng sut cao c th chu c n vi trm ampere. Diode chnh luch yu l loi Si. Hai c tnh k thut c bn ca Diode chnh lu l dng thun ti av in p ngc ti a (in p sp ). Hai c tnh ny do nh sn xut cho bit.

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Kiu mu diode vi in tr ng:

Khi in th phn cc thun vt qu in th ngng VK, dng in qua diode tngnhanh trong lc in th qua hai u diode VD cng tng (tuy chm) ch khng phi lhng s nh kiu mu trn. chnh xc hn, lc ny ngi ta phi ch n gimth qua hai u in tr ng r0.

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Th d:

T c tuyn V-I ca diode 1N917(Si), xc nh in tr ng r0 v tm im iu hnhQ(ID v VD) khi n c dng trong mch hnh bn.

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Bc 2: vi ID =4,77mA, ta xc nh c im Q (VD=0,9V)

Bc 3: v tip tuyn ti Q vi c tuyn tm in th offset V0.

V0=0,74V

V d: Xem mch dng diode 1N917 vi tn hiu nh VS(t)=50 Sint (mV).

Tm in th VD(t) ngang qua diode, bit rng in tr rB ca hai vng bn dn P-N l10?.

Gii:

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Theo v d trc, vi kiu mu in th ngng ta c VD=0,7V v ID=4,77mA.

T ta tm c in tr ni rd:

rd =26mV

ID= 26mV4,77mA = 5,45

rac=10 + 0,45=10,45?

Mch tng ng xoay chiu:

in th nh Vdm ngang qua diode l Vdm =rac

R + racVm =

15,4515, 45+3000 .50

Vdm=0,256 Sint (mV).

Vy in th tng cng ngang qua diode l:

VD(t) = 700mV + 0,256 Sin t (mV).

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Kiu mu tn hiu rng v hiu ng tn s.

Khi diode c dng vi ngun tn hiu xoay chiu tn hiu bin ln, kiu mu tnhiu nh khng th p dng c. v vy, ngi ta dng kiu mu mt chiu tuyn tnh.

Kt qu l na chu k dng ca tn hiu, diode dn v xem nh mt ngt in ngmch. na chu k m k tip, diode b phn cc nghch v c vai tr nh mt ngtin h mch. Tc dng ny ca diode c gi l chnh lu na sng (mch chnh lus c kho st k gio trnh mch in t).

p ng trn ch ng khi tn s ca ngun xoay chiu VS(t) thp-th d nh in 50/60Hz, tc chu k T=20ms/16,7ms-khi tn s ca ngun tn hiu ln cao (chu k hngnano giy) th ta phi quan tm n thi gian chuyn tip t bn k dng sang bn km ca tn hiu.

Khi tn s ca tn hiu cao, in th ng ra ngoi bn k dng (khi diode c phncc thun), bn k m ca tn hiu cng qua c mt phn v c dng nh hnh v.

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Ch l tn s ca ngun tn hiu cng cao th thnh phn bn k m xut hin ng racng ln.

Hiu ng ny do in dung khuch tn CD ca ni P-N kh ln khi c phn cc thun(CD c tr t 2000pF n 15000pF). Tc dng ca in dung ny lm cho diode khngth thay i tc thi t trng thi dn sang trng thi ngng dn m phi mt i mt thigian (thng c gi l thi gian hi phc, kiu mu diode phi k n tc dng cain dung ca ni.

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Diode tch sng.

Cng lm nhim v nh diode chnh lu nhng thng vi tn hiu c bin nh vtn s cao. Diode tch sng thng c ch to c dng thun nh v c th l Ge haySi nhng diode Ge c dng nhiu hn v in th ngng VK nh.

Diode schottky:

Ta thy nh hng ca thi gian hi phc (tc thi gian chuyn mch) ln dng sngng ra ca mch chnh lu. rt ngn thi gian hi phc. Cc ht ti in phi dichuyn nhanh, vng him phi hp. Ngoi ra, cn phi to iu kin cho s ti hp gial trng v in t d dng v nhanh chng hn. l nguyn tc ca diode schottky.

Ta thy trong diode schottky, thng ngi ta dng nhm thay th cht bn dn loiP v cht bn dn loi N l Si. Do nhm l mt kim loi nn ro in th trong diodeschottky gim nh nn in th ngng ca diode schottky khong 0,2V n 0,3V.

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l diode schottky c in th bo ho ngc ln hn diode Si v in th sp cngnh hn diode Si.

Diode n p (diode Zener):

Nh kho st phn trc, khi in th phn cc nghch ca diode ln, nhng htti in sinh ra di tc dng nhit b in trng mnh trong vng him tng vn tcv ph v cc ni ho tr trong cht bn dn. C ch ny c chng cht v sau cng tac dng in ngc rt ln. Ta ni diode ang trong vng b ph hu theo hin tngtuyt v gy h hng ni P-N.

Ta cng c mt loi ph hu khc do s ph hu trc tip cc ni ho tr di tc dngca in trng. S ph hu ny c tnh hon nghch, ngha l khi in trng ht tcdng th cc ni ho tr c lp li, ta gi hin tng ny l hiu ng Zener.

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* nh hng ca nhit :

Khi nhit thay i, cc ht ti in sinh ra cng thay i theo:

Vi cc diode Zener c in th Zener VZ < 5V th khi nhit tng, in thZener gim.

Vi cc diode c in th Zener VZ>5V (cn c gi l diode tuyt -diodeavalanche) li c h s nhit dng (VZ tng khi nhit tng).

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Kiu mu l tng ca diode Zener:

Do tnh cht trn, diode zener thng c dng ch to in th chun.

Th d: mch tao in th chun 4,3V dng diode zener 1N749 nh sau:

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Khi cha mc ti vo, th d ngun VS=15V, th dng qua zener l:

I =VS VZ

R =15 4,3

470 = 22,8mA

* Kiu mu ca diode zener i vi in tr ng:

Thc t, trong vng zener, khi dng in qua diode tng, in th qua zener cng tngcht t ch khng phi c nh nh kiu mu l tng.

Ngi ta nh ngha in tr ng ca diode l:

r = ZZ =VZT VZO

IZT

Trong : VZO l in th nghch bt u dng in tng.

VZT l in th ngang qua hai u diode dng in s dng IZT

Diode bin dung: (Varicap Varactor diode)

Phn trn ta thy, s phn b in tch dng v m trong vng him thay i khiin th phn cc nghch thay i, to ra gia hai u diode mt in dung:

CT = QV =

AWd

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in dung chuyn tip CT t l nghch vi rng ca vng him, tc t l nghch viin th phn cc.

c tnh trn c ng dng ch to diode bin dung m tr s in dung s thayi theo in th phn cc nghch nn cn c gi l VVC diode (voltage-variablecapacitance diode). in dung ny c th thay i t 5pF n 100pF khi in th phncc nghch thay i t 3 n 25V.

Diode hm (Tunnel diode)

c ch to ln u tin vo nm 1958 bi Leo-Esaki nn cn c gi l diode Esaki.y l mt loi diode c bit c dng khc vi nhiu loi diode khc. Diode hm cnng pha cht ngoi lai ln hn diode thng rt nhiu (c vng P ln vng N)

c tuyn V-I c dng nh sau:

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Khi phn cc nghch, dng in tng theo in th. Khi phn cc thun, in th thp,dng in tng theo in th nhng khi ln n nh A (VP IP), dng in li t nggim trong khi in th tng. S bin thin nghch ny n thung lng B (VV IV). Sau, dng in tng theo in th nh diode thng c cng cht bn dn cu to. ctnh c th ca diode hm ty thuc vo cht bn dn cu to Ge, Si, GaAs (galiumAsenic), GaSb (galium Atimonic) Vng AB l vng in tr m (thay i t khong50 n 500 mV). Diode c dng trong vng in tr m ny. V tp cht cao nn vnghim ca diode hm qu hp (thng khong 1/100 ln rng vng him ca diodethng), nn cc ht ti in c th xuyn qua mi ni theo hin tng chui hm nnc gi l diode hm.

T s Ip/Iv rt quan trng trong ng dng. T s ny khong 10:1 i vi Ge v 20:1 ivi GaAs.

Mch tng ng ca diode hm trong vng in tr m nh sau:

Ls: Biu th in cm ca diode, c tr s t 1nH n 12nH.

RD: in tr chung ca vng P v N.

CD: in dung khuch tn ca vng him.

Th d, diode hm Ge 1N2939: Ls=6nH, CD=5pF,Rd=-152?, RD=1,5?

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Diode c vng him hp nn thi gian hi phc nh, dng tt tn s cao. Nhc imca diode hm l vng in tr m phi tuyn, vng in tr m li in th thp nnkh dng vi in th cao, nng cht pha cao nn mun gim nh phi ch to mngmanh. Do , diode hm dn dn b diode schottky thay th.

ng dng thng dng ca diode hm l lm mch dao ng tn s cao.

Bi tp cui chng

1. Dng kiu mu l tng v in th ngng ca diode tnh dng in I1, I2,ID2 trong mch in sau:

1. I2Tnh dng in I1 v VO trong mch sau (dng kiu mu l tng v in thngng ca diode)

1. Tnh IZ, VO trong mch in sau khi R2 = 50? v khi R2 = 200?. Cho bitZener s dng c VZ = 6V.

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Cu to cn bn ca BJTTransistor lng cc gm c hai mi P-N ni tip nhau, c pht minh nm 1947 bihai nh bc hc W.H.Britain v J.Braden, c ch to trn cng mt mu bn dnGermanium hay Silicium

Ta nhn thy rng, vng pht E c pha m (nng cht ngoi lai nhiu), vng nnB c pha t v vng thu C li c pha t hn na. Vng nn c kch thc rt hp(nh nht trong 3 vng bn dn), k n l vng pht v vng thu l vng rng nht.Transistor NPN c p ng tn s cao tt hn transistor PNP. Phn sau tp trung khost trn transistor NPN nhng i vi transistor PNP, cc c tnh cng tng t.

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C ch hot ng ca transistor lng ccTrong ng dng thng thng (khuch i), ni pht nn phi c phn cc thuntrong lc ni thu nn phi c phn cc nghch.

V ni pht nn c phn cc thun nn vng him hp li. Ni thu nn c phn ccnghch nn vng him rng ra.

Nhiu in t t cc m ca ngun VEE i vo vng pht v khuch tn sang vng nn.Nh ta bit, vng nn c pha tp cht t v rt hp nn s l trng khng nhiu, do lng l trng khuch tn sang vng pht khng ng k.

Do vng nn hp v t l trng nn ch c mt t in t khuch tn t vng pht qua tihp vi l trng ca vng nn. Hu ht cc in t ny khuch tn thng qua vng thuv b ht v cc dng ca ngun VCC.

Cc in t t do ca vng pht nh vy to nn dng in cc pht IE chy t cc phtE. Cc in t t vng thu chy v cc dng ca ngun VCC to ra dng in thu ICchy vo vng thu.

Mt khc, mt s t in t l ht in thiu s ca vng nn chy v cc dng cangun VEE to nn dng in IB rt nh chy vo cc nn B.

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Nh vy, theo nh lut Kirchoff, dng in IE l tng ca cc dng in IC v IB.

Ta c: IE = IC + IB

Dng IB rt nh (hng microampere) nn ta c th coi nh: IE # IC

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Transistor trng thi cha phn ccTa bit rng khi pha cht cho (donor) vo thanh bn dn tinh khit, ta c cht bndn loi N. Cc in t t do (cn tha ca cht cho) c mc nng lng trung bnh gn di dn in (mc nng lng Fermi c nng ln). Tng t, nu cht pha lcht nhn (acceptor), ta c cht bn dn loi P. Cc l trng ca cht nhn c mc nnglng trung bnh nm gn di ho tr hn (mc nng lng Fermi gim xung).

Khi ni P-N c xc lp, mt ro in th s c to ra ti ni. Cc in t t dotrong vng N s khuch tn sang vng P v ngc li, cc l trng trong vng P khuchtn sang vng N. Kt qu l ti hai bn mi ni, bn vng N l cc ion dng, bn vngP l cc ion m. Chng to ra ro in th.

Hin tng ny cng c thy ti hai ni ca transistor. Quan st vng him, ta thyrng kch thc ca vng him l mt hm s theo nng cht pha. N rng vngcht pha nh v hp vng cht pha m.

Hnh sau y m t vng him trong transistor NPN, s tng quan gia mc nnglng Fermi, di dn in, di ho tr trong 3 vng, pht nn, thu ca transistor

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Cc cch rp transistor v li dng inKhi s dng, transistor c rp theo mt trong 3 cch cn bn sau:

Rp theo kiu cc nn chung (1) Rp theo kiu cc pht chung (2) Rp theo kiu cc thu chung (3)

Trong 3 cch rp trn, cc chung chnh l cc c ni mass v dng chung cho c haing vo v ng ra.

Trong mi cch rp, ngi ta nh ngha li dng in mt chiu nh sau:

li dng in ca transistor thng c dng l li trong cch rp cc phtchung v cc nn chung. li dng in trong cch rp cc pht chung c cho bi:

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Nh vy: IC= DC.IB

Nhng: IE = IC + IB = DC.IB+IB

IE = (DC + 1).IB

li dng in trong cch rp cc nn chung c cho bi:

DC c tr s t vi chc n vi trm, thm ch c th ln n hng ngn. DC c tr t0,95 n 0,999 tu theo loi transistor. Hai thng s DC v DC c nh sn xutcho bit.

T phng trnh cn bn:

IE = IC + IB

Ta c: IC = IE IB

* Ghi ch: cc cng thc trn l tng qut, ngha l vn ng vi transistor PNP.

Ta ch dng in thc chy trong hai transistor PNP v NPN c chiu nh sau:

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Th d:

Mt transistor NPN, Si c phn cc sau cho IC = 1mA v IB = 10A.

Tnh DC, IE, DC.

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Dng in r trong transistorV ni thu nn thng c phn cc nghch nn cng c mt dng in r ngc (boho nghch) i qua mi ni nh trong trng hp diode c phn cc nghch. Dngin r ngc ny c k hiu l ICBO, c nh sn xut cho bit, c m t bnghnh v sau:

y l dng in i t cc thu qua cc nn khi cc pht h. Hnh v sau y cho tathy thnh phn cc dng in chy trong transistor bao gm c dng in ICBO.

Nh vy, ta c: IC = DCIE + ICBO

Nu ICBO xp x 0, xem nh khng ng k.

Ta c: IC DCIE

l cng thc l tng m ta thy phn trn. Ngoi ta, t phng trnh dng incn bn:

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IE = IB + IC

Suy ra, IC = DC(IC + IB) + ICBO

IC = DCIC + DC IB + ICBO

Thay vo phng trnh trn, ta tm c:

IC = DCIB + (DC + 1)ICBO

Ngi ta t: ICEO = (DC + 1)ICBO v phng trnh trn c vit li:

IC = DCIB + ICEO

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c tuyn V-I ca transistorNgi ta thng ch n 3 loi c tuyn ca transistor:

c tuyn ng vo. c tuyn ng ra c tuyn truyn

im cn ch : tu theo loi transistor v cc cch rp m ngun V11, V22 phi mcng cc (sao cho ni thu nn phn cc nghch v ni pht nn phn cc thun). CcAmpe k I1, I2, cc volt k V1 v V2 cng phi mc ng chiu.

Chng ta kho st hai cch mc cn bn:L

Mc theo kiu cc nn chung:

Mch in nh sau:

c tuyn ng vo (input curves).

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Nhn xt:

Khi ni thu nn h, c tuyn c dng nh c tuyn ca diode khi phn ccthun.

in th ngng (knee voltage) ca c tuyn gim khi VCB tng.

c tuyn ng ra (output curves)

L c tuyn biu din s thay i ca dng in cc thu IC theo in th thu nn VCBvi dng in cc pht IE lm thng s.

c tuyn c dng nh sau: Ta ch n ba vng hot ng ca transistor.

Vng tc ng: Ni nn pht phn cc thun, ni thu nn phn cc nghch. Trong vngny c tuyn l nhng ng thng song song v cch u. Trong cc ng dng thngthng, transistor c phn cc trong vng tc ng.

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Vng ngng: ni nn pht phn cc nghch (IE=0), ni thu nn phn cc nghch. Trongvng ny transistor khng hot ng.

Vng bo ho: ni pht nn phn cc thun, ni thu nn phn cc thun. Trong cc ngdng c bit, transistor mi c phn cc trong vng ny.

Mc theo kiu cc pht chung.

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c tuyn ng vo:

c tuyn ng ra:

Biu din dng in cc thu IC theo in th ng ra VCE vi dng in ng vo IB cchn lm thng s.

Dng c tuyn nh sau:

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Ta thy cng c 3 vng hot ng ca transistor: vng bo ho, vng tc ngv vng ngng.

Khi ni tt VBE (tc IB=0) dng in cc thu xp x dng in r ICEO.

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c tuyn truyn: (Transfer characteristic curve)

i vi transistor Si, vng hot ng c VBE nm trong khong 0,5-0,8V. Trong vngny, c tuyn truyn c dng hm m. vng bo ho, dng IC tng nhanh khi VBEthay i. vng ngng, khi VBE cn nh, dng r qua transistor ICES rt nh, thngxp x ICBO.

Ngay c trong vng hot ng, khi VBE thay i mt lng nh (t dng IB thy i)th dng IC thay i mt lng kh ln. V th, trong cc ng dng, ngi ta dng inth cc nn VBE lm in th iu khin v cc B cn gi l cc khin.

nh hng ca nhit ln cc c tuyn ca BJT.

Nh ta thy, cc tnh cht in ca cht bn dn u thay i theo nhit . Do ,cc c tuyn ca BJT u thay i khi nhit thay i.

Khi nhit tng, cc dng in r ca cc thu (ICBO,Iceo, ICES) u tng. Khi nhit tng, cc li in th DC, DC cng tng. Khi nhit tng, in th phn cc thun (in th ngng) ni nn pht VBE

gim. Thng thng, VBE gim 2,2mV khi nhit tng 10C.

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Dng in r ICBO tng gp i khi nhit tng 80C trong transistor Si.

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im iu hnh ng thng ly in mtchiu

xc nh im tnh iu hnh Q v ng thng ly in mt chiu, ngi ta thngdng 3 bc:

1. Mch ng vo:

Ta c: VBE + REIE - VEE = 0

IE =VEE VBE

RE

Ch l VBE = 0,7V vi BJT l Si v VBE = 0,3V nu BJT l Ge.

2. T cng thc IC = DCIE IE.

Suy ra dng in cc thu IC.

3. Mch ng ra:

Ta c: VCB - VCC + RCIC = 0

IC = VCBRC

+VCCRC

y l phng trnh ng thng ly in mt chiu (ng thng ly in tnh). Trnc tuyn ra, giao im ca ng thng ly in vi IE tng ng (thng s) ca ctuyn ra chnh l im tnh iu hnh Q.

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Ta ch rng:

Khi VCB = 0 IC = ISH =VCCRC

(Dng in bo ho) Khi IC = 0 (dng ngng), ta c: VCB = VCC = VOC

Mt s nhn xt:

thy nh hng tng i ca RC,VCC, IE ln im iu hnh, ta xem v d sau y:

nh hng ca in tr cc thu RC: RC = 1,5K?; 2K?; 3 K?

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Nh vy, khi gi cc ngun phn cc VCC, VEE v RE c nh, thay i RC, im iuhnh Q s chy trn c tuyn tng ng vi IE = 3mA. Khi RC tng th VCB gim vngc li.

nh hng ca ngun phn cc ni thu nn VCC.

Nu gi IE l hng s (tc VEE v RE l hng s), RC l hng s, thay i ngun VCC,ta thy: Khi VCC tng th VCB tng, khi VCC gim th VCB gim.

nh hng ca IE ln im iu hnh:

Nu ta gi RC v VCC c nh, thay i IE (tc thay i RE hoc VEE) ta thy: khi IEtng th VCB gim (tc IC tng), khi IC gim th VCB tng (tc IC gim).

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Khi IE tng th IC tng theo v tin dn n tr ISH. Transistor dn dn i vo vng boho. Dng ti a ca IC, tc dng bo ho gi l IC(sat). Nh vy:

IC(sat) = ISH =VCCRC

Lc ny, VCB gim rt nh v xp x bng 0V (tht s l 0,2V).

Khi IE gim th IC gim theo. Transistor i dn vo vng ngng, VCB lc gi lVCB(off) v IC = ICBO.

Nh vy, VCB(off) = VOC = VCC.

Vng bo ho v vng ngng l vng hot ng khng tuyn tnh ca BJT.

i vi mch cc pht chung, ta cng c th kho st tng t.

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Kiu mu mt chiu ca BJT

xc nh im tnh iu hnh Q v ng thng ly in mt chiu, ngi ta thngdng 3 bc:

1. Mch ng vo:

Ta c: VBE + REIE - VEE = 0

IE =VEE VBE

RE

Ch l VBE = 0,7V vi BJT l Si v VBE = 0,3V nu BJT l Ge.

2. T cng thc IC = DCIE IE.

Suy ra dng in cc thu IC.

3. Mch ng ra:

Ta c: VCB - VCC + RCIC = 0

IC = VCBRC

+VCCRC

y l phng trnh ng thng ly in mt chiu (ng thng ly in tnh). Trnc tuyn ra, giao im ca ng thng ly in vi IE tng ng (thng s) ca ctuyn ra chnh l im tnh iu hnh Q.

Ta ch rng:

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Khi VCB = 0 IC = ISH =VCCRC

(Dng in bo ho) Khi IC = 0 (dng ngng), ta c: VCB = VCC = VOC

Mt s nhn xt:

thy nh hng tng i ca RC,VCC, IE ln im iu hnh, ta xem v d sau y:

nh hng ca in tr cc thu RC: RC = 1,5K?; 2K?; 3 K?

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Nh vy, khi gi cc ngun phn cc VCC, VEE v RE c nh, thay i RC, im iuhnh Q s chy trn c tuyn tng ng vi IE = 3mA. Khi RC tng th VCB gim vngc li.

nh hng ca ngun phn cc ni thu nn VCC.

Nu gi IE l hng s (tc VEE v RE l hng s), RC l hng s, thay i ngun VCC,ta thy: Khi VCC tng th VCB tng, khi VCC gim th VCB gim.

nh hng ca IE ln im iu hnh:

Nu ta gi RC v VCC c nh, thay i IE (tc thay i RE hoc VEE) ta thy: khi IEtng th VCB gim (tc IC tng), khi IC gim th VCB tng (tc IC gim).

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Khi IE tng th IC tng theo v tin dn n tr ISH. Transistor dn dn i vo vng boho. Dng ti a ca IC, tc dng bo ho gi l IC(sat). Nh vy:

IC(sat) = ISH =VCCRC

Lc ny, VCB gim rt nh v xp x bng 0V (tht s l 0,2V).

Khi IE gim th IC gim theo. Transistor i dn vo vng ngng, VCB lc gi lVCB(off) v IC = ICBO.

Nh vy, VCB(off) = VOC = VCC.

Vng bo ho v vng ngng l vng hot ng khng tuyn tnh ca BJT.

i vi mch cc pht chung, ta cng c th kho st tng t.

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BJT vi tn hiu xoay chiuM hnh ca BJT:

y l m hnh ca mt mch khuch i rp theo kiu cc nn chung. ng vo vng ra, ta c hai t lin lc C1 v C2 c in dung nh th no dung khng XC khnh tn s ca ngun tn hiu c th xem nh ni tt (Short circuit) i vi tn hiuxoay chiu v c th xem nh h mch (open circuit) i vi in th phn cc.

Mch tng ng mt chiu nh sau:

y l mch m chng ta kho st phn trc. Ngun in th xoay chiu VS(t) khia vo mch s lm cho thng s transistor thay i. Ngoi thnh phn mt chiu cnc thnh phn xoay chiu ca ngun tn hiu to ra chng ln.

Ngha l: iB(t) = IB + ib(t)

iC(t) = IC + ic(t)

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iE(t) = IE + ie(t)

vCB(t) = VCB + vcb(t)

vBE(t) = VBE + vbe(t)

Thnh phn tc thi = thnh phn DC + thnh phn xoay chiu.

Ngoi ra, ta cng c in tr rb ca vng bn dn nn pht ( y, ta c th coi nh yl in tr gia B v B). Do gia B v C phn cc nghch nn c mt in tr r0 rtln. Tuy nhin, vn c dng in ic = .ie = ib chy qua v c coi nh mc songsong vi r0.

* l li dng in xoay chiu trong cch mc nn chung:

Thng thng hoc ac gn bng DC v xp x bng n v.

* l li dng in xoay chiu trong cch mc cc pht chung.

Thng thng hoc ac gn bng DC v cng thay i theo dng ic.

Tr s , cng c nh sn xut cung cp.

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in dn truyn (transconductance)

Ta thy rng, dng in cc thu IC thay i theo in th nn pht VBE. Ngi ta c thbiu din s thay i ny bng mt c tuyn truyn (transfer curve) ca transistor. ctuyn ny ging nh c tuyn ca diode khi phn cc thun

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Ngi ta nh ngha in dn truyn ca transistor l:

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Tng tr vo ca transistor:

Ta c hai loi tng tr vo: tng tr vo nhn t cc pht E v tng tr vo nhn t ccnn B.

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Tng tr vo nhn t cc pht E:

Theo m hnh ca transistor i vi tn hiu xoay chiu, ta c mch tng ng ngvo nh sau:

Tng tr vo nhn t cc nn B:

Xem m hnh nh ngha sau (hnh 37):

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Mch tng ng ng vo:

Hiu ng Early (Early effect)

Ta xem li c tuyn ng ra ca transistor trong cch mc cc pht chung. Nm 1952.J.Early thuc phng th nghim Bell nghin cu v hin tng ny c mang tnng. ng nhn xt:

nhng gi tr cao ca dng in cc thu IC, dng IC tng nhanh theo VCE (c tuync dc ng).

nhng gi tr thp ca IC, dng IC tng khng ng k khi VCE tng (c tuyn gnnh nm ngang).

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Mch tng ng xoay chiu ca BJT:

Vi tn hiu c bin nh v tn s khng cao lm, ngi ta thng dng hai kiu musau y:

Kiu hn tp: (hybrid- )

Vi m hnh tng ng ca transistor v cc tng tr vo, tng tr ra, ta c mchtng ng hn tp nh sau:

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Kiu mu r e : (r e model)

Cng vi m hnh tng ng xoay chiu ca BJT, cc tng tr vo, tng tr ra, ta cmch tng ng kiu re. Trong kiu tng ng ny, ngi ta thng dng chungmt mch cho kiu rp cc pht chung v cc thu chung v mt mch ring cho nnchung.

Kiu cc pht chung v thu chung:

Kiu cc nn chung

Kiu thng s h: (h-parameter)

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T hai phng trnh ny, ta c mch in tng ng theo kiu thng s h:

So snh vi kiu hn tp, ta thy rng:

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Cc thng s h do nh sn xut cho bit.

Trong thc hnh, r0 hay

mc song song vi ti. Nu ti khng ln lm (khong vi chc K? tr li), trong mchtng ng, ngi ta c th b qua r0 (khong vi trm K?).

Bi tp cui chng

1. Tnh in th phn cc VC, VB, VE trong mch:

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Cu to cn bn ca JFET

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Nu so snh vi BJT, ta thy: cc thot D tng ng vi cc thu C, cc ngun Stng ng vi cc pht E v cc cng G tng ng vi cc nn B.

JFET knh N tng ng vi transistor NPN.

JFET knh P tng ng vi transistor PNP

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Cng ging nh transistor NPN c s dng thng dng hn transistor PNP do dngtt hn tn s cao. JFET knh N cng thng dng hn JFET knh P vi cng mt ldo. Phn sau, ta kho st JFET knh N, vi JFET knh P, cc tnh cht cng tng t.

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C ch hot ng ca JFET

By gi, nu ta mc cc ngun S v cc cng G xung mass, ngha l in th VGS=0V.iu chnh in th VDS gia cc thot v cc ngun, chng ta s kho st dng inqua JFET khi in th VDS thay i.

V vng thot n+ ni vi cc dng v vng cng G ni vi cc m ca ngun in VDSnn ni PN vng thot c phn cc nghch, do vng him y rng ra (xemhnh v)

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Khi VDS cn nh, dng in t t cc m ca ngun in n vng ngun (to ra dngIS), i qua thng l v tr v cc dng ca ngun in (to ra dng in thot ID).

Nu thng l c chiu di L, rng W v dy T th in tr ca n l:

; Trong , l in tr sut ca thng l. in tr sut l hm s theo nng chtpha.

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Khi VDS cn nh (vi volt), in tr R ca thng l gn nh khng thay i nn dngID tng tuyn tnh theo VDS. Khi VDS ln, c tuyn khng cn tuyn tnh na do Rbt u tng v thng l hp dn. Nu ta tip tc tng VDS n mt tr s no th haivng him chm nhau, ta ni thng l b nghn (pinched off).

Tr s VDS thng l bt u b nghn c gi l in th nghn VP (pinched offvoltage). tr s ny, ch c cc in t c nng lng cao trong di dn in mi c sc xuyn qua vng him vo vng thot v b ht v cc dng ca ngun inVDS to ra dng in thot ID.

Nu ta c tip tc tng VDS, dng in ID gn nh khng thay i v c gi l dngin bo ho thot - ngun IDSS (ch : k hiu IDSS khi VGS=0V).

By gi, nu ta phn cc cng-ngun bng mt ngun in th m VGS (phn ccnghch), ta thy vng him rng ra v thng l hp hn trong trng hp VGS=0V. Do in tr ca thng l cng ln hn.

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Khi VDS cn nh, ID cng tng tuyn tnh theo VDS, nhng khi VDS ln, thng l bnghn nhanh hn, ngha l tr s VDS thng l nghn nh hn trong trng hpVGS=0V v do , dng in bo ho ID cng nh hn IDSS.

Chm c tuyn ID=f(VDS) vi VGS l thng s c gi l c tuyn ra ca JFET mctheo kiu cc ngun chung

Khi VGS cng m, dng ID bo ho cng nh. Khi VGS m n mt tr no , vnghim chim gn nh ton b thng l v cc in t khng cn nng lng vtqua c v khi ID = 0. Tr s ca VGS lc gi l VGS(off). Ngi ta chng minhc tr s ny bng vi in th nghn.

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V Vp chnh l hiu th phn cc ngc cc ni P-N va cho cc vng him chmnhau. V vy, trong vng bo ho ta c:

V ni cng ngun c phn cc nghch, dng in IG chnh l dng in r ngc nnrt nh, do dng in chy vo cc thot D c xem nh bng dng in ra khicc ngun S. ID # IS.

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c tuyn truyn ca JFET

Ngi ta chng minh c khi VDS c tr s lm nghn thng l (JFET hot ng trongvng bo ho), ID v VGS tho mn h thc:

hay

Phng trnh ny c gi l phng trnh truyn ca JFET. Cc thng s ID v VGS(off)c nh sn xut cho bit.

l: VGS v VGS(off) m trong JFET thng l n v dng trong thng l p.

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Ngi ta cng c th biu th s thay i ca dng in thot ID theo in th cngngun VGS trong vng bo ho bng mt c tuyn gi l c tuyn truyn bng cchv ng biu din ca phng trnh truyn trn.

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nh hng ca nhit trn JFETNh ta thy trong JFET, ngi ta dng in trng kt hp vi s phn cc nghchca ni P-N lm thay i in tr (tc dn in) ca thng l ca cht bn dn.cng nh BJT, cc thng s ca JFET cng rt nhy i vi nhit , ta s kho st quahai tc ng chnh ca nhit :

Khi nhit tng, vng him gim, do rng ca thng l tng ln, do in trca thng l gim. (ID tng)

Khi nhit tng, linh ng ca cc ht ti in gim (ID gim)

Do thng l tng rng theo nhit nn VGS(off) cng tng theo nhit . Thc nghimcho thy VGS(off)hayVP tng theo nhit vi h s 2,2mV/10C.

T cng thc:

Cho thy tc dng ny lm cho dng in ID tng ln. Ngoi ra, do linh ng caht ti in gim khi nhit tng lm cho in tr ca thng l tng ln nn dng inIDSS gim khi nhit tng, hiu ng ny lm cho ID gim khi nhit tng.

Tng hp c hai hiu ng ny, ngi ta thy nu chn tr s VGS thch hp th dngthot ID khng i khi nhit thay i. Ngi ta chng minh c tr s ca VGS l:

vi VP l in th nghn nhit bnh thng.

Cc hnh v sau y m t nh hng ca nhit trn cc c tuyn ra, c tuyntruyn v c tuyn ca dng ID theo nhit khi VGS lm thng s.

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Ngoi ra, mt tc dng th ba ca nhit ln JFET l lm pht sinh cc ht ti introng vng him gia thng l-cng v to ra mt dng in r cc cng IGSS (gateleakage current). Dng IGSS c nh sn xut cho bit. dng r IGSS chnh l dng inphn cc nghch ni P-N gia cc cng v cc ngun. Dng in ny l dng in rcng-ngun khi ni tt cc ngun vi cc thot. Dng IGSS tng gp i khi nhit tng ln 100C.

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Mosfet loi him (depletion mosfet demosfet)Ta thy rng khi p mt in th m vo JFET knh N th vng him rng ra. S giatng ca vng him lm cho thng l hp li v in tr ca thng l tng ln. Kt qusau cng l to ra dng in ID nh hn IDSS.

By gi, nu ta p in th dng VGS vo JFET knh N th vng him s hp li (dophn cc thun cng ngun), thng l rng ra v in tr thng l gim xung, kt qul dng in ID s ln hn IDSS.

Trong cc ng dng thng thng, ngi ta u phn cc nghch ni cng ngun (VGSm i vi JFET knh N v dng i vi JFET knh P) v c gi l iu hnh theokiu him.

JFET cng c th iu hnh theo kiu tng (VGS dng i vi JFET knh N v m ivi JFET knh P) nhng t khi c ng dng, v mc ch ca JFET l tng tr voln, ngha l dng in IG cc cng - ngun trong JFET s lm gim tng tr vo, do thng thng ngi ta gii hn tr s phn cc thun ca ni cng - ngun ti a l0,2V (tr s danh nh l 0,5V).

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Tuy JFET c tng tr vo kh ln nhng cng cn kh nh so vi n chn khng. tng tng tr vo, ngi ta to mt loi transistor trng khc sao cho cc cngcch in hn cc ngun. Lp cch in l Oxyt bn dn SiO2 nn transistor c gil MOSFET.

Ta phn bit hai loi MOSFET: MOSFET loi him v MOSFET loi tng.

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Hnh sau y m t cu to cn bn MOSFET loi him (DE - MOSFET) knh N vknh P.

Ch rng DE - MOSFET c 4 cc: cc thot D, cc ngun S, cc cng G v thn U(subtrate). Trong cc ng dng thng thng, thn U c ni vi ngun S.

DE-MOSFET hot ng, ngi ta p mt ngun in VDD vo cc thot v ccngun (cc dng ca ngun in ni vi cc thot D v cc m ni vi cc ngunS trong DE-MOSFET knh N v ngc li trong DE-MOSFET knh P). in th VGSgia cc cng v cc ngun c th m (DE-MOSFET knh N iu hnh theo kiu him)hoc dng (DE-MOSFET knh N iu hnh theo kiu tng)

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Khi VGS = 0V (cc cng ni thng vi cc ngun), in t di chuyn gia cc m cangun in VDD qua knh n- n vng thot (cc dng ca ngun in VDD) to radng in thot ID. Khi in th VDS cng ln th in tch m cng G cng nhiu (docng G cng in th vi ngun S) cng y cc in t trong knh n- ra xa lm chovng him rng thm. Khi vng him va chn ngang knh th knh b nghn v dngin thot ID t n tr s bo ho IDSS.

Khi VGS cng m, s nghn xy ra cng sm v dng in bo ho ID cng nh.

Khi VGS dng (iu hnh theo kiu tng), in tch dng ca cc cng ht cc int v mt tip xc cng nhiu, vng him hp li tc thng l rng ra, in tr thng lgim nh. iu ny lm cho dng thot ID ln hn trong trng hp VGS = 0V.

V cc cng cch in hn khi cc ngun nn tng tr vo ca DE-MOSFET ln hnJFET nhiu. Cng v th, khi iu hnh theo kiu tng, ngun VGS c th ln hn 0,2V.Th nhng ta phi c gii hn ca dng ID gi l IDMAX. c tuyn truyn v c tuynng ra nh sau:

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Nh vy, khi hot ng, DE-MOSFET ging ht JFET ch c tng tr vo ln hn vdng r IGSS nh hn nhiu so vi JFET.

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Mosfet loi tng (enhancement mosfet e-mosfet)MOSFET loi tng cng c hai loi: E-MOSFET knh N v E-MOSFET knh P.

V mt cu to cng ging nh DE-MOSFET, ch khc l bnh thng khng c thngl ni lin gia hai vng thot D v vng ngun S.

M hnh cu to v k hiu c din t bng hnh v sau y

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Khi VGS < 0V, ( E-MOSFET knh N), do khng c thng l ni lin gia hai vngthot ngun nn mc d c ngun in th VDD p vo hai cc thot v ngun, in tcng khng th di chuyn nn khng c dng thot ID (ID # 0V). Lc ny, ch c mtdng in r rt nh chy qua.

Khi VGS>0, mt in trng c to ra vng cng. Do cng mang in tch dngnn ht cc in t trong nn p- (l ht ti in thiu s) n tp trung mt i din cavng cng. Khi VGS ln, lc ht mnh, cc in t n tp trung nhiu v to thnhmt thng l tm thi ni lin hai vng ngun S v thot D. in th VGS m t

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dng in thot ID bt u tng c gi l in th thm cng - ngun (gate-to-sourcethreshold voltage) VGS(th). Khi VGS tng ln hn VGS(th), dng in thot ID tip tctng nhanh.

Ngi ta chng minh c rng:

Trong : ID l dng in thot ca E-MOSFET

K l hng s vi n v AV2

VGS l in th phn cc cng ngun.

VGS(th) l in th thm cng ngun.

Hng s K thng c tm mt cch gin tip t cc thng s do nh sn xut cungcp.

Th d: Mt E-MOSFET knh N c VGS(th) =3,8V v dng in thot ID = 10mA khiVGS = 8V. Tm dng in thot ID khi VGS = 6V.

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Xc nh im iu hnhTa xem m hnh ca mt mch khuch i tn hiu nh dng JFET knh N mc theokiu cc ngun chung

Mch tng ng mt chiu (tc mch phn cc) nh sau:

Cng ging nh transistor thng (BJT), xc nh im iu hnh Q, ngi ta dng3 bc:

p dng nh lut Krichoff mch ng vo tm VGS.

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y l phng trnh biu din ng phn cc (bias line) v giao im ca ngthng ny vi c tuyn truyn l im iu hnh Q.

Nh c tuyn truyn, ta c th xc nh c dng thot ID.

- xc nh in th VDS, ta p dng nh lut Kirchoff cho mch ng ra:

VDD = RDID + VDS

VDS = VDD RDID

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y l phng trnh ca ng thng ly in tnh. Giao im ca ng thng ny vic tuyn ng ra vi VGS = -VGG = -1V chnh l im tnh iu hnh Q.

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Fet vi tn hiu xoay chiu v mch tngng vi tn hiu nhGi s ta p mt tn hiu xoay chiu hnh sin vs(t) c bin in th nh l 10mV vong vo ca mt mch khuch i cc ngun chung dng JFET knh N

C1 v C2 l 2 t lin lc, c chn sao cho c dung khng rt nh tn s ca tn hiuv c th c xem nh ni tt tn s tn hiu.

Ngun tn hiu vs(t) s chng ln in th phn cc VGS nn in th cng ngun vGS(t) thi im t l:

vGS(t) = VGS + Vgs(t)

= -1V + 0,01sin t (V)

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Ngun tn hiu c in th nh nh nn in th cng ngun vn lun lun m. Nhc tuyn truyn, chng ta thy rng im iu hnh s di chuyn khi VGS thay I theotn hiu. thi im khi VGS t m hn, dng thot iD(t) tng v khi VGS m nhiu hn,dng thot iD(t) gim. Vy dng in thot iD(t) thay i cng chiu vi vGS(t) v c trs quanh dng phn cc ID tnh (c gi s l 12,25mA). gia tng ca iD(t) v gim ca iD(t) bng nhau vi tn hiu nh (gi s l 0,035mA). (Xem hnh trang sau).

S thay i dng in thot iD(t) s lm thay i hiu s in th gia cc thot v ccngun.

Ta c vDS(t) = VDD iD(t).RD. Khi iD(t) c tr s ti a, th vDS(t) c tr s ti thiu vngc li. iu ny c ngha l s thay i ca vDS(t) ngc chiu vi s thay i cadng iD(t) tc ngc chiu vi s thay i ca hiu th ng vo vGS(t), ngi ta boin th ng ra ngc pha - lch pha 180o so vi in th tn hiu ng vo.

Ngi ta nh ngha li ca mch khuch i l t s nh i nh ca hiu th tnhiu ng ra v tr s nh i nh ca hiu th tn hiu ng vo:

Trong trng hp ca th d trn:

AV=2,87 ?-180o

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Ngi ta dng du - biu din lch pha 180o

Mch tng ng ca FET vi tn hiu nh:

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Do dng ig rt nh nn FET c tng tr ng vo l:

Cc phng trnh ny c din t bng gin sau y gi l mch tng ngxoay chiu ca FET.

Ring i vi E-MOSFET, do tng tr vo r rt ln, nn trong mch tng ngngi ta c th b r

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in dn truyn (transconductance) ca jfetv demosfetCng tng t nh BJT, mt cch tng qut ngi ta nh ngha in dn truyn caFET l t s:

in dn truyn c th c suy ra t c tuyn truyn, chnh l dc ca tiptuyn vi c tuyn truyn ti im iu hnh Q

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Trong : gm: l in dn truyn ca JFET hay DE-MOSFET vi tn hiu nh

gmo: l gm khi VGS= 0V

VGS: in th phn cc cng - ngun

VGS(off): in th phn cc cng - ngun lm JFET hay DE-MOSFET ngng.

Phng trnh trn cho ta thy s lin h gia in dn truyn gm vi dng in thot IDti im iu hnh Q. gmo c xc nh t cc thng s IDSS v VGS(off) do nh snxut cung cp.

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in dn truyn ca e-mosfetDo cng thc tnh dng in thot ID theo VGS ca E-MOSFET khc vi JFET v DE-MOSFET nn in dn truyn ca n cng khc.

Trong :

gm: l in dn truyn ca E-MOSFET cho tn hiu nh

K: l hng s vi n v Amp/volt2

ID: Dng din phn cc cc thot D

Ta thy gm ty thuc vo dng in thot ID, nu gi gm1 l in dn truyn ca E-MOSFET ng vi dng thot ID1 v gm2 l in dn truyn ca E-MOSFET ng vidng thot ID2

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Tng tr vo v tng tr ra ca fet- Ging nh BJT, ngi ta cng dng hiu ng Early nh ngha tng tr ra caFET ( vng bo ha, khi VDS tng, dng in ID cng hi tng v chm c tuyn racng hi t ti mt im gi l in th Early).

Nu gi VA l in th Early ta c:

ro nh vy thAy i theo dng thot ID v c tr s khong vi M? n hn

10M?

- Do JFET thng c dng theo kiu him (phn cc nghch ni cng - ngun) nntng tr vo ln (hng trm M?). Ring E-MOSFET v DE-MOSFET do cc cng cchin hn khi cc ngun nn tng tr vo rt ln (hng trm M?). Kt qu l ngi tac th xem gn ng tng tr vo ca FET l v hn.

Vi FET : r ?

Trong cc mch s dng vi tn hiu nh ngi ta c th dng mch tng ng choFET nh hnh (a) hoc hnh (b). Nu ti khng ln lm, trong mch tng ng ngita c th b c ro

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CMOS tuyn tnh (linear cmos)Nu ta c mt E-MOSFET knh P v mt E-MOSFET knh N mc nh hnh sau y tac mt linh kin t hp v c gi l CMOS (Complementary MOSFET).

Tht ra n c cu trc nh sau:

Cu trc CMOS c dng rt nhiu trong IC tuyn tnh v IC s

+ By gi ta xt mch cn bn nh trn, ta th xem p ng ca CMOS khi tn hiu voc dng xung vung nh hnh v. Mch ny c ng dng lm cng o v l tngcui ca OP-AMP (IC thut ton).

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- Khi vi = 5V (0 t t1); E-MOSFET knh P ngng v vGS(t)=0V, trong lc E-MOSFET knh N dn mnh v vGS(t)=5V nn in th ng ra vo(t)=0V.

- Khi vi(t)=0V (t t1), E-MOSFET knh P dn in mnh (v vGS(t) = -5V) trong lc E-MOSFET knh N khng dn in (v vGS(t) = 0V) nn in th ng ra vo(t)=VDD=5V.

Nh vy, tc dng ca CMOS l mt mch o (inverter)

Ta xem mt mch khuch i n gin dng CMOS tuyn tnh:

- Khi vi(t) dng, E-MOSFET knh N dn in mnh hn v E-MOSFET knh P btu dn in yu hn. Do vo(t) gim.

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- Khi vi(t) dng, E-MOSFET knh P dn in mnh hn v E-MOSFET knh N btu dn in yu hn, nn vo(t) tng.

Nh vy ta thy tn hiu ng vo v ng ra ngc pha nhau (lnh pha 180o)

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Mosfet cng sut v-mos v d-mosCc transistor trng ng (JFET v MOSFET) m ta kho st trn ch thch hpcho cc mch c bin tn hiu nh nh tin khuch i, trn sng, khuch i cao tn,trung tn, dao ng nm 1976, ngi ta pht minh ra loi transistor trng c cngsut va, n ln vi kh nng dng thot n vi chc ampere v cng sut c th lnn vi chc Watt.

V-MOS:

Tht ra y l mt loi E-MOSFET ci tin, cng l khng c sn thng l v iu hnhtheo kiu tng. s khc nhau v cu trc E-MOSFET v V-MOS c trnh by bnghnh v sau:

Khi VGS dng v ln hn VGS(th), thng l c hnh thnh dc theo rnh V v dngelectron s chy thng t hai ngun S n cc thot D. V l do ny nn c gi lV-MOS (Vertical MOSFET).

D-MOS:

Cng l mt loi E-MOSFET hot ng theo kiu tng, ng dng hin tng khuch tni (double-diffused) nn c gi l D-MOS. C cu trc nh sau:

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Cc c tnh hot ng ca V-MOS v D-MOS cng ging nh E-MOSFET. Ngoi ra,cc c im ring ca V-MOS v D-MOS l:

- in tr ng rds khi hot ng rt nh (thng nh hn 1?)

- C th khuch i cng sut tn s rt cao

- Di thng ca mch khuch i cng sut c th ln n vi chc MHz

- V-MOS v D-MOS cng c knh N v knh P, nhng knh N thng dng hn

- V-MOS v D-MOS cng c k hiu nh E-MOSFET

H FET c th tm tt nh sau

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Bi tp cui chng

1. Tnh VD, v in dn truyn gm trong mch:

1. Trong mch in sau, tnh in th phn cc VD v in dn truyn gm.

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SCR (thyristor silicon controlled rectifier)Cu to v c tnh:

SCR c cu to bi 4 lp bn dn PNPN (c 3 ni PN). Nh tn gi ta thy SCR lmt diode chnh lu c kim sot bi cng silicium. Cc tp xc kim loi c tora cc cc Anod A, Catot K v cng G.

Nu ta mc mt ngun in mt chiu VAA vo SCR nh hnh sau. mt dng in nhIG kch vo cc cng G s lm ni PN gia cc cng G v catot K dn pht khi dngin anod IA qua SCR ln hn nhiu. Nu ta i chiu ngun VAA (cc dng ni vicatod, cc m ni vi anod) s khng c dng in qua SCR cho d c dng in kchIG. Nh vy ta c th hiu SCR nh mt diode nhng c thm cc cng G v SCRdn in phi c dng in kch IG vo cc cng.

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Ta thy SCR c th coi nh tng ng vi hai transistor PNP v NPN lin kt nhauqua ng nn v thu

Khi c mt dng in nh IG kch vo cc nn ca Transistor NPN T1 tc cng G caSCR. Dng in IG s to ra dng cc thu IC1 ln hn, m IC1 li chnh l dng nn IB2ca transistor PNP T2 nn to ra dng thu IC2 li ln hn trc Hin tng ny c tiptc nn c hai transistor nhanh chng tr nn bo ha. Dng bo ha qua hai transistorchnh l dng anod ca SCR. Dng in ny ty thuc vo VAA v in tr ti RA.

C ch hot ng nh trn ca SCR cho thy dng IG khng cn ln v ch cn tn titrong thi gian ngn. Khi SCR dn in, nu ta ngt b IG th SCR vn tip tc dnin, ngha l ta khng th ngt SCR bng cc cng, y cng l mt nhc im caSCR so vi transistor.

Ngi ta ch c th ngt SCR bng cch ct ngun VAA hoc gim VAA sao cho dngin qua SCR nh hn mt tr s no (ty thuc vo tng SCR) gi l dng in duytr IH (hodding current).

c tuyn Volt-Ampere ca SCR:

c tuyn ny trnh by s bin thin ca dng in anod IA theo in th anod-catodVAK vi dng cng IG coi nh thng s.

- Khi SCR c phn cc nghch (in th anod m hn in th catod), ch c mtdng in r rt nh chy qua SCR.

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- Khi SCR c phn cc thun (in th anod dng hn in th catod), nu ta ni tt(hoc h) ngun VGG (IG=0), khi VAK cn nh, ch c mt dng in rt nh chyqua SCR (trong thc t ngi ta xem nh SCR khng dn in), nhng khi VAK t nmt tr s no (ty thuc vo tng SCR) gi l in th quay v VBO th in thVAK t ng st xung khong 0,7V nh diode thng. Dng in tng ng by gichnh l dng in duy tr IH. T by gi, SCR chuyn sang trng thi dn in v cc tuyn gn ging nh diode thng.

Nu ta tng ngun VGG to dng kch IG, ta thy in th quay v nh hn v khidng kch IG cng ln, in th quay v VBO cng nh.

Cc thng s ca SCR:

Sau y l cc thng s k thut chnh ca SCR

- Dng thun ti a:

L dng in anod IA trung bnh ln nht m SCR c th chu ng c lin tc. Trongtrng hp dng ln, SCR phi c gii nhit y . Dng thun ti a ty thuc vomi SCR, c th t vi trm mA n hng trm Ampere.

- in th ngc ti a:

y l in th phn cc nghch ti a m cha xy ra s hy thc (breakdown). y ltr s VBR hnh trn. SCR c ch to vi in th nghch t vi chc volt n hngngn volt.

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- Dng cht (latching current):

L dng thun ti thiu gi SCR trng thi dn in sau khi SCR t trng thingng sang trng thi dn. Dng cht thng ln hn dng duy tr cht t SCR cngsut nh v ln hn dng duy tr kh nhiu SCR c cng sut ln.

- Dng cng ti thiu (Minimun gate current):

Nh thy, khi in th VAK ln hn VBO th SCR s chuyn sang trng thi dn inm khng cn dng kch IG. Tuy nhin trong ng dng, thng ngi ta phi to ra mtdng cng SCR dn in ngay. Ty theo mi SCR, dng cng ti thiu t di 1mAn vi chc mA. Ni chung, SCR c cng sut cng ln th cn dng kch ln. Tuynhin, nn ch l dng cng khng c qu ln, c th lm hng ni cng-catod caSCR.

- Thi gian m (turn on time):

L thi gian t lc bt u c xung kch n lc SCR dn gn bo ha (thng l 0,9 lndng nh mc). Thi gian m khong vi S. Nh vy, thi gian hin din ca xungkch phi lu hn thi gian m.

- Thi gian tt (turn off time):

tt SCR, ngi ta gim in th VAK xung 0Volt, tc dng anod cng bng 0. Thnhng nu ta h in th anod xung 0 ri tng ln ngay th SCR vn dn in mc dkhng c dng kch. Thi gian tt SCR l thi gian t lc in th VAK xung 0 nlc ln cao tr li m SCR khng dn in tr li. Thi gian ny ln hn thi gian m,thng khong vi chc S. Nh vy, SCR l linh kin chm, hot ng tn s thp,ti a khong vi chc KHz.

- Tc tng in th dv/dt:

Ta c th lm SCR dn in bng cch tng in th anod ln n in th quay v VBOhoc bng cch dng dng kch cc cng. Mt cch khc l tng in th anod nhanhtc dv/dt ln m bn thn in th V anod khng cn ln. Thng s dv/dt l tc tngth ln nht m SCR cha dn, vt trn v tr ny SCR s dn in. L do l c mtin dung ni Cb gia hai cc nn ca transistor trong m hnh tng ng ca SCR.dng in qua t l: icb = Cb dVdt . Dng in ny chy vo cc nn ca T1. Khi dV/dt ln th icb ln sc kch SCR. Ngi ta thng trnh hin tng ny bng cch mcmt t C v in tr R song song vi SCR chia bt dng icb.

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- Tc tng dng thun ti a di/dt:

y l tr s ti a ca tc tng dng anod. Trn tr s ny SCR c th b h. L dol khi SCR chuyn t trng thi ngng sang trng thi dn, hiu th gia anod v catodcn ln trong lc dng in anod tng nhanh khin cng sut tiu tn tc thi c th quln. Khi SCR bt u dn, cng sut tiu tn tp trung gn vng cng nn vng nyd b h hng. Kh nng chu ng ca di/dt ty thuc vo mi SCR.

SCR hot ng in th xoay chiu

Khi SCR hot ng in th xoay chiu tn s thp (th d 50Hz hoc 60Hz) th vn tt SCR c gii quyt d dng. Khi khng c xung kch th mng in xung gn0V, SCR s ngng. D nhin bn k m SCR khng hot ng mc d c xung kch.

tng cng sut cho ti, ngi ta cho SCR hot ng ngun chnh lu ton k.

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V in 50Hz c chu k T=1/50=20nS nn thi gian in th xp x 0V lm ngngSCR.

Vi ng dng n gin:

Mch n khn cp khi mt in:

Bnh thng n 6V chy sng nh ngun in qua mch chnh lu. Lc ny SCRngng dn do b phn cc nghch, accu c np qua D1, R1. Khi mt in, ngun inaccu s lm thng SCR v thp sng n.

Mch np accu t ng (trang sau)

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- Khi accu np cha y, SCR1 dn, SCR2 ngng

- Khi accu np y, in th cc dng ln cao, kch SCR2 lm SCR2 dn, chia btdng np bo v accu.

- VR dng chnh mc bo v (gim nh dng np)

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TRIAC (triod ac semiconductor switch)Thng c coi nh mt SCR lng hng v c th dn in theo hai chiu. Hnh sauy cho thy cu to, m hnh tng ng v cu to ca Triac.

Nh vy, ta thy Triac nh gm bi mt SCR PNPN dn in theo chiu t trn xungdi, kch bi dng cng dng v mt SCR NPNP dn in theo chiu t di ln kchbi dng cng m. Hai cc cn li gi l hai u cui chnh (main terminal).

- Do u T2 dng hn u T1, Triac dn in ta c th kch dng cng dng v khiu T2 m hn T1ta c th kch dng cng m.

- Nh vy c tuyn V-I ca Triac c dng sau:

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- Tht ra, do s tng tc ca vng bn dn, Triac c ny theo 4 cch khc nhau, ctrnh by bng hnh v sau y:

Cch (1) v cch (3) nhy nht, k n l cch (2) v cch (4). Do tnh cht dn in chai chiu, Triac dng trong mng in xoay chiu thun li hn SCR. Th d sau ycho thy ng dng ca Triac trong mng in xoay chiu.

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SCS (silicon controlled switch)SCS cn c gi l Tetrode thyristor (thyristor c 4 cc). V mt cu to, SCS gingnh SCR nhng c thm mt cng gi l cng anod nn cng kia ( SCR) c gi lcng catod.

Nh vy, khi ta p mt xung dng vo cng catod thi SCS dn in. Khi SCS anghot ng, nu ta p mt xung dng vo cng anod th SCS s ngng dn. Nh vy,i vi SCS, cng catod dng m SCS, v cng anod dng tt SCS. Tuy c khnng nh SCR, nhng thng ngi ta ch ch to SCS cng sut nh (phn ln divi trm miniwatt) v do cng catod rt nhy (ch cn kch cng catod khong vi chcA) nn SCS c ng dng lm mt switch in t nhy.

V d sau l mt mch bo ng dng SCS nh mt cm bin in th:

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ng vo thng ngi ta mc mt ming kim loi, khi s tay vo, SCS dn in Ledtng ng chy sng, Relais hot ng ng mch bo ng hot ng.

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DIACV cu to, DIAC ging nh mt SCR khng c cc cng hay ng hn l mt transistorkhng c cc nn. Hnh sau y m t cu to, k hiu v mch tng ng ca DIAC.

Khi p mt hiu in th mt chiu theo mt chiu nht nh th khi n in th VBO,DIAC dn in v khi p hiu th theo chiu ngc li th n tr s -VBO, DIAC cngdn in, DIAC th hin mt in tr m (in th hai u DIAC gim khi dng inqua DIAC tng). T cc tnh cht trn, DIAC tng ng vi hai Diode Zener mci u. Thc t, khi khng c DIAC, ngi ta c th dng hai Diode Zener c in thZener thch hp thay th. (Hnh 17)

Trong ng dng, DIAC thng dng m Triac. Th d nh mch iu chnh sngca bng n (Hnh 18)

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bn k dng th in th tng, t np in cho n in th VBO th DIAC dn, todng kch cho Triac dn in. Ht bn k dng, Triac tm ngng. n bn k m tC np in theo chiu ngc li n in th -VBO, DIAC li dn in kch Triac dnin. Ta thay i VR thay i thi hng np in ca t C, do thay i gc dnca Triac a n lm thay i sng ca bng n.

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Ujt (unijunction transistor transistor cni)Transistor thng (BJT) gi l Transistor lng cc v c hai ni PN trong lc UJT chc mt c nht ni P-N. Tuy khng thng dng nh BJT, nhng UJT c mt s ctnh c bit nn mt thi gi vai tr quan trng trong cc mch to dng sng vnh gi.

Cu to v c tnh ca UJT:

Hnh sau y m t cu to n gin ho v k hiu ca UJT

Mt thi bn dn pha nh loi n- vi hai lp tip xc kim loi hai u to thnh haicc nn B1 v B2. Ni PN c hnh thnh thng l hp cht ca dy nhm nh ngvai tr cht bn dn loi P. Vng P ny nm cch vng B1 khong 70% so vi chiu dica hai cc nn B1, B2. Dy nhm ng vai tr cc pht E.

Hnh sau y trnh by cch p dng in th mt chiu vo cc cc ca UJT khost cc c tnh ca n.

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- Khi cha p VEE vo cc pht E (cc pht E h) thi bn dn l mt in tr vingun in th VBB, c k hiu RBB v gi l in tr lin nn (thng c tr s t4 K? n 10 K?). T m hnh tng ng ta thy Diod c dng din t ni P-Ngia vng P v vng n-. in tr RB1 v RB2 din t in tr ca thi bn dn n-. Nhvy:

- By gi, ta cp ngun VEE vo cc pht v nn B1 (cc dng ni v cc pht). KhiVEE=0V (ni cc pht E xung mass), v VA c in th dng nn Diod c phncc nghch v ta ch c mt dng in r nh chy ra t cc pht. tng VEE ln dn,dng in IE bt u tng theo chiu dng (dng r ngc IE gim dn, v trit tiu,sau dng dn). Khi VE c tr s

VE=VD+VA

VE=0,5V + ? VB2B1 ( y VB2B1 = VBB) th Diod phn cc thun v bt u dn inmnh.

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in th VE=0,5V + ? VB2B1=VP c gi l in th nh (peak-point voltage) caUJT.

Khi VE=VP, ni P-N phn cc thun, l trng t vng pht khuch tn vo vng n- vdi chuyn n vng nn B1, lc l trng cng ht cc in t t mass ln. V dnin ca cht bn dn l mt hm s ca mt in t di ng nn in tr RB1 gim.Kt qu l lc dng IE tng v in th VE gim. Ta c mt vng in tr m.

in tr ng nhn t cc pht E trong vng in tr m l: rd = VEIE

Khi IE tng, RB1 gim trong lc RB2 tb nh hng nn in tr lin nn RBB gim.Khi IE ln, in tr lin nn RBB ch yu l RB2. Kt thc vng in tr m l vngthung lng, lc dng IE ln v RB1 qu nh khng gim na (ch l dng ra ccnn B1) gm c dng in lin nn IB cng vi dng pht IE ) nn VE khng gim mbt u tng khi IE tng. Vng ny c gi l vng bo ha.

Nh vy ta nhn thy:

- Dng nh IP l dng ti thiu ca cc pht E t UJT hot ng trong vng intr m. Dng in thung lng IV l dng in ti a ca IE trong vng in tr m.

- Tng t, in th nh VP l in th thung lng VV l in th ti a v ti thiu caVEB1 t UJT trong vng in tr m.

Trong cc ng dng ca UJT, ngi ta cho UJT hot ng trong vng in tr m, munvy, ta phi xc nh in tr RE IP

Cc thng s k thut ca UJT v vn n nh nhit cho nh:

Sau y l cc thng s ca UJT:

- in tr lin nn RBB: l in tr gia hai cc nn khi cc pht h. RBB tng khinhit tng theo h s 0,8%/1oC

- T s ni ti:

T s ny cng c nh ngha khi cc pht E h.

- in th nh VP v dng in nh IP. VP gim khi nhit tng v in th ngngca ni PN gim khi nhit tng. Dng IP gim khi VBB tng.

- in th thung lng VV v dng in thung lng IV. C VV v IV u tng khi VBBtng.

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- in th cc pht bo ha VEsat: l hiu in th gia cc pht E v cc nn B1 co IE=10mA hay hn v VBB 10V. Tr s thng thng ca VEsat l 4 volt (ln hnnhiu so vi diod thng).

n nh nhit cho nh: in th nh VP l thng s quan trng nht ca UJT. Nh thy, s thay i ca in th nh VP ch yu l do in th ngng ca ni PN v t s? thay i khng ng k.

Ngi ta n nh nhit cho VP bng cch thm mt in tr nh R2 (thng khong vitrm ohm) gia nn B2 v ngun VBB. Ngoi ra ngi ta cng mc mt in tr nh R1cng khong vi trm ohm cc nn B1 ly tn hiu ra.

Khi nhit tng, in tr lin nn RBB tng nn in th lin nn VB2B1 tng. ChnR2 sao cho s tng ca VB2B1 b tr s gim ca in th ngng ca ni PN. Tr caR2 c chn gn ng theo cng thc: R2

(0,4 0,8)RBBVBB

Ngoi ra R2 cn ph thuc vo cu to ca UJT. Tr chn theo thc nghim khong vitrm ohm.

ng dng n gin ca UJT:

Mch dao ng th gin (relaxation oscillator)

Ngi ta thng dng UJT lm thnh mt mch dao ng to xung. Dng mch v trs cc linh kin in hnh nh sau:

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Khi cp in, t C1 bt u np in qua in tr RE. (Diod pht-nn 1 b phn ccnghch, dng in pht IE xp x bng khng). in th hai u t tng dn, khi n inth nh VP, UJT bt u dn in. T C1 phng nhanh qua UJT v in tr R1. inth hai u t (tc VE) gim nhanh n in th thung lng VV. n y UJT bt ungng v chu k mi lp li.

Dng UJT to xung kch cho SCR

- Bn k dng nu c xung a vo cc cng th SCR dn in. Bn k m SCR ngng.

- iu chnh gc dn ca SCR bng cch thay i tn s dao ng ca UJT.

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Diod shockleyDiod shockley gm c 4 lp bn dn PNPN (diod 4 lp) nhng ch c hai cc. Cu toc bn v k hiu cng vi c tuyn Volt-Ampere khi phn cc thun c m t hnh v sau y:

Ta thy c tuyn ging nh SCR lc dng cng IG=0V, nhng in th quay v VBOca Diod shockley nh hn nhiu. Khi ta tng in th phn cc thun, khi in thanod-catod ti tr s VBO th Diod shockley bt u dn, in th hai u gim nh vsau hot ng nh Diod bnh thng.

p dng thng thng ca Diod shockley l dng kch SCR. Khi phn cc nghch,Diod shockley cng khng dn in.

- Bn k dng, t C np in n in th VBO th Diod shockley dn in, kch SCRdn.

Bn k m, Diod shockley ngng, SCR cng ngng.

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GTO (gate turn off switch)GTO l mt linh kin c 4 lp bn dn PNPN nh SCR. cu to v k hiu c m tnh sau:

Tuy c k hiu khc vi SCR v SCS nhng cc tnh cht th tng t. S khc bitc bn cng l s tin b ca GTO so vi SCR hoc SCS l c th m hoc tt GTOch bng mt cng (m GTO bng cch a xung dng vo cc cng v tt GTO bngcch a xung m vo cc cng).

- So vi SCR, GTO cn dng in kch ln hn (thng hng trm mA)

- Mt tnh cht quan trng na ca GTO l tnh chuyn mch. Thi gian m ca GTOcng ging nh SCR (khong 1s), nhng thi gian tt (thi gian chuyn t trng thidn in sang trng thi ngng dn) th nh hn SCR rt nhiu (khong 1s GTO vt 5s n 30s SCR). Do GTO dng nh mt linh kinc chuyn mch nhanh.GTO thng c dng rt ph bin trong cc mch m, mch to xung, mch iuho in th mch sau y l mt ng dng ca GTO to tn hiu rng ca kt hpvi Diod Zener.

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Khi cp in, GTO dn, anod v catod xem nh ni tt. C1 np in n in th ngunVAA, lc VGK

PUT (Programmable UnijunctionTransistor)Nh tn gi, PUT ging nh mt UJT c c tnh thay i c. Tuy vy v cu to,PUT khc hn UJT

l cng G nm vng N gn anod nn PUT dn in, ngoi vic in thanod ln hn in th catod, in th anod cn phi ln hn in th cng mt in thngng ca ni PN.

Tuy nhin, nn nh l UJT, RB1v RB2 l in tr ni ca UJT, Trong lc PUT, RB1v RB2 l cc in tr phn cc bn ngoi.

c tuyn ca dng IA theo in th cng VAK cng ging nh UJT

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Tuy PUT v UJT c c tnh ging nhau nhng dng in nh v thung lng ca PUTnh hn UJT

+ Mch dao ng th gin dng PUT

Ch trong mch dng PUT, ng x ca t in l anod. Tn hiu ra c s dngthng ly catod (v c th dng kch SCR nh UJT)

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nh sngSng v tuyn trong h thng truyn thanh, truyn hnh, nh sng pht n tia X trongy khoa Tuy c cc cng dng khc nhau nhng li c chung mt bn cht v c gil sng in t hay bc x in t. im khc nhau c bn ca sng in t l tn shay bc sng. Gia tn s v bc sng lin h bng h thc

Trong c l vn tc nh sng = 3.108m/s

f l tn s tnh bng Hz

Bc sng tnh bng m. Ngoi ra ngi ta thng dng cc c s:

m = 10-6m ; nm = 10-9m v Amstron = = 10-10m

S khc bit v tn s dn n mt s khc bit quan trng khc l ta c th thy csng in t hay khng. Mt ngi ch thy c sng in t trong mt di tn srt hp gi l nh sng thy c hay thng gi tt l nh sng. V pha tn s thphn gi l bc x hng ngoi (infrared) v pha tn s cao hn gi l bc x t ngoi(ultraviolet).

Ta ch c th thy c bc x c tn s khong 4.10-14Hz (tc bc sng 750nm) ntn s khong 7,8.1014Hz (tc bc sng khong 380nm)

Trong vng nh sng thy c, nu ch c mt khong ngn ca di tn s ni trn thcm gic ca mt ghi nhn c 7 mu:

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Ch l gii hn trn ch c tnh cch tng i. S khc nhau v tn s li dn nmt s khc bit quan trng na l nng lng bc x. Nng lng bc x t l vitn s theo cng thc: E=h.f vi h: hng s planck = 6,624.10-34J.sec

Nh ta thy, bin trung bnh ca ph c gi l cng sng v c o bng nv footcandles. Th d ngun sng l mt bng n trn, th mt im cng xa ngun,cng sng cng yu nhng s lng nh sng ta ra trong mt gc khi (hnh nn)l khng i v c gi l quang thng. n v ca quang thng l Lumens (Lm) hayWatt.

1 Lm = 1,496.10-10 watt

n v ca cng nh sng l foot-candles (fc), Lm/ft2hay W/m2. Trong :

1 Lm/ft2 = 1 fc = 1,609.10-12 W/m2

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Quang in tr (photoresistance)L in tr c tr s cng gim khi c chiu sng cng mnh. in tr ti (khi khngc chiu sng - trong bng ti) thng trn 1M?, tr s ny gim rt nh c th di100? khi c chiu sng mnh

Nguyn l lm vic ca quang in tr l khi nh sng chiu vo cht bn dn (c thl Cadmium sulfide CdS, Cadmium selenide CdSe) lm pht sinh cc in t t do,tc s dn in tng ln v lm gim in tr ca cht bn dn. Cc c tnh in v nhy ca quang in tr d nhin ty thuc vo vt liu dng trong ch to.

V phng din nng lng, ta ni nh sng cung cp mt nng lng E=h.f ccin t nhy t di ha tr ln di dn in. Nh vy nng lng cn thit h.f phi lnhn nng lng ca di cm.

Vi ng dng ca quang in tr:

Quang in tr c dng rt ph bin trong cc mch iu khin

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Mch bo ng:

Khi quang in tr c chiu sng (trng thi thng trc) c in tr nh, in thcng ca SCR gim nh khng dng kch nn SCR ngng. Khi ngun sng b chn,R tng nhanh, in th cng SCR tng lm SCR dn in, dng in qua ti lm chomch bo ng hot ng.

Ngi ta cng c th dng mch nh trn, vi ti l mt bng n c th chy sngv m v tt vo ban ngy. Hoc c th ti l mt relais iu khin mt mch bong c cng sut ln hn.

Mch m in t ng v m dng in AC:

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Ban ngy, tr s ca quang in tr nh. in th im A khng m Diac nnTriac khng hot ng, n tt. v m, quang tr tng tr s, lm tng in th imA, thng Diac v kch Triac dn in, bng n sng ln.

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Quang diod (photodiode)Ta bit rng khi mt ni P-N c phn cc thun th vng him hp v dng thun lnv do ht ti in a s (in t cht bn dn loi N v l trng cht bn dn loiP) di chuyn to nn. Khi phn cc nghch, vng him rng v ch c dng in r nh(dng bo ha nghch I0) chy qua.

By gi ta xem mt ni P-N c phn cc nghch. Th nghim cho thy khi chiu sngnh sng vo mi ni (gi s diod c ch to trong sut), ta thy dng in nghchtng ln gn nh t l vi quang thng trong lc dng in thun khng tng. Hin tngny c dng ch to quang diod.

Khi nh sng chiu vo ni P-N c nng lng lm pht sinh cc cp in t - ltrng st hai bn mi ni lm mt ht ti in thiu s tng ln. Cc ht ti in