scr, diac & triac

A/. SCR : Lan Hng hc l Semiconductor Controlled Rectifier (bn dn nn dng c iu khin) nhng sao thy trn mng ngi ta li hay vit Silicon Controlled Rectifier (linh kin silic nn dng iu khin c). C l l vt liu bn dn Silicon dng ph bin ch to bn dn, nn ni gp vy cho ... chc hay sao .

Mun bit v SCR th cn nm r v BJT.

Thay v ch c 3 lp bn dn (hai mi ni) th ngi ta ch to linh kin c 4 lp bn dn (3 mi ni).

Trong hnh cho thy 4 lp bn dn xem nh l 2 transistor PNP v NPN kt hp nhau thnh mt cu trc mi. Cu trc bn dn (semiconductor) ny c tn l SCR v n c kh nng khi dn mt thi gian (pha), iu khin (control) c qu trnh nn dng (rectifier). K hiu ca SCR v th m ging nh mt diod c anod A + cathode K vi cc gate G.

Phn tch v dng cho thy khi A - K c in p thun, cha c dng chy qua SCR. thi im t(on) c xung dng thun trn G th NPN dn --> PNP kch dn --> dng chy t Anode A qua Cathode K --> SCR dn --> c dng I(scr) qua SCR.

V SCR dn mi n khi no I(scr) --> 0 n mt gii hn cut, hoc khi anode A c in p nghch (m so vi K) th SCR tt. sau phi c xung kch I(g) th SCR mi dn chu k mi. Thi im t(on) qui nh pha dn ca SCR --> quyt nh cng sut v in p nn dng biu kin.

SCR thng c ch to vi cng sut rt ln, in p nghch rt cao. Nhng ng dng cn SCR dng v p b ngi ta vn thng dng 2 transistor khc "cht" rp thnh SCR ph hp vi yu cu. V d trong cc mch bo v qu p, qu dng v.v...

ng dng ca SCR th nhiu v k, nh l ng dng chnh lu c iu khin, v l th nht vn nghch lu (DC-AC) vi cng sut hng trm KW cho l nung, l ti, l luyn thp cao tn, v ngun siu m c ln trong ty ra kim loi v.v....

B/. Diac v Triac :

I/. Diac : Diac l mt cu trc 5 lp bn dn, xem nh 4 diod bn dn. Trong mch, khi in p trn hai cc (khng phn cc) ca diac c mt in p ln th n dn mt xung . V d Db30 th khi in p trn 2 cc t 30V, n s dn dng ngn i qua thnh mt xung ri ngng dn.

Ni khc i, diac ng ngt do in p trn hai cc ca n.

Diac thng c dng iu khin SCR hay triac mt cch n gin v hu hiu.

II/. Triac : Tng t nh diac, triac (TRIode for Alternating Current) l phn t bn dn gm nm lp bn dn, to nn cu trc p-n-p-n n. Nhng c thm cc khin Gate.

Mch ng hiu ca triac l hai SCR ni nhau mt cch c bit (xem hnh).

Trong hnh cho thy hai SCR kt ni c mt gate chung cho hai chiu dng in --> cc cc c 3 in cc l: A1, A2, G. V vy m triac rt hu dng iu khin pha (do iu khin cng sut v p biu kin) ca dng in xoay chiu.

Khi cc G v A1 c in th m so vi A1 th triac m. Cc A1 ng vai tro ant , cc A2 ng vai tr catt, dong in chy t A1 sang A2.Khi cc G v A2 c in th dng so vi A1 th triac m cc A2 ng vai tr ant, A1 ng vai tr catt, dng in chy t A2 sang A1.

hnh : dng in vi triac iu khin pha

S di y l mt dimmer iu khin cng sut xoay chiu cho mt n t tim. Mch cng c th dng cho iu khin tc qut v cp vi mt L-C ni song song vi qut in th ch ca n (qut "tai voi" Nga dng cch ny).

trong : diac = Db30 ; VR = 100K ; C = 103 ; triac = BT05 --> BT10

Dng kch I(g) ca triac c th l dng m hay dng. Nu kch bng p m (-) th tr tuyt i ca dng kch m s phi ln hn dng kch dng nhng s n nh hn khi kch dng dng.

Triac cng thng c ch to vi cng sut ln, dng cho PowerBoss, cho iu khin pha iu tc u my Diesel- in v.v... c th n hng vn KW.