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Chng XI - Mch ngun1. B ngun trong cc mch in t . Trong cc mch in t ca cc thit b nh Radio -Cassette, mlpy, Ti vi mu, u VCD v v... chng s dng ngun mt chiu DC cc mc in p khc nhau, nhng ngoi zc cm ca cc thit b ny li cm trc tip vo ngun in AC 220V 50Hz , nh vy cc thit b in t cn c mt b phn chuyn i t ngun xoay chiu ra in p mt chiu , cung cp cho cc mch trn, b phn chuyn i bao gm : Bin p ngun : H th t 220V xung cc in p thp hn nh 6V, 9V, 12V, 24V v v ... Mch chnh lu : i in AC thnh DC. Mch lc Lc gn xoay chiu sau chnh lu cho ngun DC phng hn. Mch n p : Gi mt in p c nh cung cp cho ti tiu th

S tng qut ca mch cp ngun. 2. Mch chnh lu bn chu k . Mch chnh lu bn chu k s dng mt Diode mc ni tip vi ti tiu th, chu k dng => Diode c phn cc thun do c dng in i qua diode v i qua ti, chu k m , Diode b phn cc ngc do khng c dng qua ti.

Dng in p u ra ca mch chnh lu bn chu k.

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3. Mch chnh lu c chu k Mch chnh lu c chu k thng dng 4 Diode mc theo hnh cu (cn gi l mch chnh lu cu) nh hnh di.

Mch chnh lu c chu k . chu k dng ( u dy pha trn dng, pha di m) dng in i qua diode D1 => qua Rti => qua diode D4 v u dy m chu k m, in p trn cun th cp o chiu ( u dy trn m, di dng) dng in i qua D2 => qua Rti => qua D3 v u dy m. Nh vy c hai chu k u c dng in chy qua ti. 4. Mch lc dng t in. Sau khi chnh lu ta thu c in p mt chiu nhp nh, nu khng c t lc th in p nhp nh ny cha th dng c vo cc mch in t , do trong cc mch ngun, ta phi lp thm cc t lc c tr s t vi trm F n vi ngn F vo sau cu Diode chnh lu.

Dng in p DC ca mch chnh lu trong hai trng hp c t v khng c t

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S trn minh ho cc trng hp mch ngun c t lc v khng c t lc. Khi cng tc K m, mch chnh lu khng c t lc tham gia , v vy in p thu c c dng nhp nh. Khi cng tc K ng, mch chnh lu c t C1 tham gia lc ngun , kt qu l in p u ra c lc tng i phng, nu t C1 c in dung cng ln th in p u ra cng bng phng, t C1 trong cc b ngun thng c tr s khong vi ngn F .

Minh ho : in dng ca t lc cng ln th in p u ra cng bng phng. Trong cc mch chnh lu, nu c t lc m khng c ti hoc ti tiu th mt cng xut khng ng k so vi cng xut ca bin p th in p DC thu c l DC = 1,4.AC 5. Mch chnh lu nhn 2 .

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S mch ngun chnh lu nhn 2 tr thnh mch chnh lu nhn 2 ta phi dng hai t ho cng tr s mc ni tip, sau u 1 u ca in p xoau chiu vo im gia hai t => ta s thu c in p tng gp 2 ln. mch trn, khi cng tc K m, mch tr v dng chnh lu thng thng . Khi cng tc K ng, mch tr thnh mch chnh lu nhn 2, v kt qu l ta thu c in p ra tng gp 2 ln.

6. Mch n p c nh dng Diode Zener.

. Mch n p to p 33V c nh cung cp cho mch d knh trong Ti vi mu T ngun 110V khng c nh thng qua in tr hn dng R1 v gim trn Dz 33V ly ra mt in p c nh cung cp cho mch d knh Khi thit k mt mch n p nh trn ta cn tnh ton in tr hn dng sao cho dng in ngc cc i qua Dz phi nh hn dng m Dz chu c, dng cc i qua Dz l khi dng qua R2 =0 Nh s trn th dng cc i qua Dz bng st p trn R1 chia cho gi tr R1 , gi dng in ny l I1 ta c I1 = (110 - 33 ) / 7500 = 77 / 7500 ~ 10mA Thng thng ta nn dng ngc qua Dz 25 mA 7. Mch n p c nh dng Transistor, IC n p . Mch n p dng Diode Zener nh trn c u im l n gin nhng nhc im l cho dng in nh ( 20mA ) . c th to ra mt in p c nh nhng cho dng in mnh hn nhiu ln ngi ta mc thm Transistor khuych i v dng nh s di y.

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Mch n p c Transistor khuych i mch trn in p ti im A c th thay i v cn gn xoay chiu nhng in p ti im B khng thay i v tng i phng. Nguyn l n p : Thng qua in tr R1 v Dz gim c nh in p chn B ca Transistor Q1, gi s khi in p chn E n Q1 gim => khi in p UBE tng => dng qua n Q1 tng => lm in p chn E ca n tng , v ngc li ... Mch n p trn n gin v hiu qu nn c s dng rt rng di v ngi ta sn xut cc loi IC h LA78.. thay th cho mch n p trn, IC LA78.. c s mch nh phn mch c mu xanh ca s trn.

IC n p h LA78.. LA7805 LA7808 IC n p 5V IC n p 8V

IC n p LA7805

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LA7809 LA7812

IC n p 9V IC n p 12V

Lu : H IC78.. ch cho dng tiu th khong 1A tr xung, khi rp IC trong mch th U in > Uout t 3 n 5V khi IC mi pht huy tc dng. 8. ng dng ca IC n p h 78.. IC n p h 78.. c dng rng ri trong cc b ngun , nh B ngun ca u VCD, trong Ti vi mu, trong my tnh v v...

ng dng ca IC n p LA7805 v LA7808 trong b ngun u VCD

9. S khi ca mch n p c hi tip .

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S khi ca mch n p c hi tip . * Mt s c im ca mch n p c hi tip : Cung cp in p mt chiu u ra khng i trong hai trng hp in p u vo thay i hoc dng tiu th ca ti thay i , tuy nhin s thay i ny phi c gii hn. Cho in p mt chiu u ra c cht lng cao, gim thiu c hin tng gn xoay chiu. * Nguyn tc hot ng ca mch. Mch ly mu s theo di in p u ra thng qua mt cu phn p to ra ( Ulm : p ly mu) Mch to p chun => gim ly mt mc in p c nh (Uc : p chun ) Mch so snh s so snh hai in p ly mu Ulm v p chun Uc to thnh in p iu khin. Mch khuch i sa sai s khuch i p iu khin, sau a v iu chnh s hot ng ca n cng xut theo hng ngc li, nu in p ra tng => thng qua mch hi tip iu chnh => n cng xut dn gim =>in p ra gim xung . Ngc li nu in p ra gim => thng qua mch hi tip iu chnh => n cng xut li dn tng => v in p ra tng ln =>> kt qu in p u ra khng thay i. 10. Phn tch hot ng ca mch ngun c hi tip trong Ti vi en trng Samsung in p u vo cn gn xoay chiu in p u ra bng phng

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Mch n p tuyn tnh trong Ti vi Samsung en trng . * ngha cc linh kin trn s . T 2200F l t lc ngun chnh, lc in p sau chnh lu 18V , y cng l in p u vo ca mch n p, in p ny c th tng gim khong 15%. Q1 l n cng xut ngun cung cp dng in chnh cho ti , in p u ra ca mc n p ly t chn C n Q1 v c gi tr 12V c nh . R1 l tr phn dng c cng xut ln ghnh bt mt phn dng in i qua n cng xut. Cu phn p R5, VR1 v R6 to ra p ly mu a vo chn B n Q2 . Diode zener Dz v R4 to mt in p chun c nh so vi in p ra. Q2 l n so snh v khuych i in p sai lch => a v iu khin s hot ng ca n cng xut Q1. R3 lin lc gia Q1 v Q2, R2 phn p cho Q1 * Nguyn l hot ng .

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in p u ra s c xu hng thay i khi in p u vo thay i, hoc dng tiu th thay i. Gi s : Khi in p vo tng => in p ra tng => in p chn E n Q2 tng nhiu hn chn B ( do c Dz gim t chn E n Q2 ln Ura, cn Ulm ch ly mt phn Ura ) do UBE gim => n Q2 dn gim => n Q1 dn gim => in p ra gim xung. Tng t khi Uvo gim, thng qua mch iu chnh => ta li thu c Ura tng. Thi gian iu chnh ca vng hi tip rt nhanh khong vi giy v c cc t lc u ra loi b, khng lm nh hng n cht lng ca in p mt chiu => kt qu l in p u ra tng i phng. Khi iu chnh bin tr VR1 , in p ly mu thay i, dn n Q2 thay i , dn n Q1 thay i => kt qu l in p ra thay i, VR1 dng iu chnh in p ra theo mun . 11. Mch ngun Ti vi ni a nht.

S mch ngun n p tuyn tnh trong Ti vi mu ni a Nht . C1 l t lc ngun chnh sau cu Diode chnh lu. C2 l t lc u ra ca mch ngun tuyn tnh. Cu phn p R4, VR1, R5 to ra in p ly mu ULM R2 v Dz to ra p chun Uc

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R3 lin lc gia Q3 v Q2, R1 nh thin cho n cng xut Q1 R6 l in tr phn dng, l in tr cng xut ln . Q3 l n so snh v khuch i p d sai Khuch i in p d sai Q1 n cng xut ngun => Ngun lm vic trong di in p vo c th thay i 10%, in p ra lun lun c nh . Bi tp : Bn c hy phn tch nguyn l hot ng ca mch ngun trn.

Chng XII - Mch dao ng1. Khi nim v mch dao ng. Mch dao ng c ng dng rt nhiu trong cc thit b in t, nh mch dao ng ni trong khi RF Radio, trong b knh Ti vi mu, Mch dao ng to xung dng , xung mnh trong Ti vi , to sng hnh sin cho IC Vi x l hot ng v v... Mch dao ng hnh Sin Mch dao ng a hi Mch dao ng nght Mch dao ng dng IC 2. Mch dao ng hnh Sin Ngi ta c th to dao ng hnh Sin t cc linh kin L - C hoc t thch anh. * Mch dao ng hnh Sin dng L - C

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Mch dao ng hnh Sin dng L - C Mach dao ng trn c t C1 // L1 to thnh mch dao ng L -C duy tr s dao ng ny th tn hiu dao ng c a vo chn B ca Transistor, R1 l tr nh thin cho Transistor, R2 l tr gnh ly ra tn hiu dao ng ra , cun dy u t chn E Transistor xung mass c tc dng ly hi tip duy tr dao ng. Tn s dao ng ca mch ph thuc vo C1 v L1 theo cng thc f = 1 / 2..( L1.C1 )1/2 * Mch dao ng hnh sin dng thch anh.

Mch to dao ng bng thch anh . X1 : l thch anh to dao ng , tn s dao ng c ghi trn thn ca thach anh, khi thch anh c cp in th n t dao ng ra sng hnh sin.thch anh thng c tn s dao

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ng t vi trm KHz n vi chc MHz. n Q1 khuych i tn hiu dao ng t thch anh v cui cng tn hiu c ly ra chn C. R1 va l in tr cp ngun cho thch anh va nh thin cho n Q1 R2 l tr ghnh to ra st p ly ra tn hiu .

Thch anh dao ng trong Tivi mu, my tnh 3. Mch dao ng a hi.

Mch dao ng a hi to xung vung * Bn c th t lp s trn vi cc thng s nh sau : R1 = R4 = 1 K R2 = R3 = 100K C1 = C2 = 10F/16V Q1 = Q2 = n C828

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Hai n Led Ngun Vcc l 6V DC Tng gi thnh lnh kin ht khong 4.000 VN * Gii thch nguyn l hot ng : Khi cp ngun , gi s n Q1 dn trc, p Uc n Q1 gim => thng qua C1 lm p Ub n Q2 gim => Q2 tt => p Uc n Q2 tng => thng qua C2 lm p Ub n Q1 tng => xc lp trng thi Q1 dn bo ho v Q2 tt , sau khong thi gian t , dng np qua R3 vo t C1 khi in p ny > 0,6V th n Q2 dn => p Uc n Q2 gim => tip tc nh vy cho n khi Q2 dn bo ho v Q1 tt, trng thi lp i lp li v to thnh dao ng, chu k dao ng ph thuc vo C1, C2 v R2, R3. 4. IC to dao ng XX555 ; XX c th l TA hoc LA v v ...

Mch dao ng to xung bng IC 555 Bn hy mua mt IC h 555 v t lp cho mnh mt mch to dao ng theo s nguyn l nh trn. Vcc cung cp cho IC c th s dng t 4,5V n 15V , ng mch mu l dng ngun, mch mu en di cng l m ngun. T 103 (10nF) t chn 5 xung mass l c nh v bn c th b qua ( khng lp cng c ) Khi thay i cc in tr R1, R2 v gi tr t C1 bn s thu c dao ng c tn s v rng xung theo mun theo cng thc.

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T = 0.7 (R1 + 2R2) C1 v f =

1.4 (R1 + 2R2) C1

T = Thi gian ca mt chu k ton phn tnh bng (s) f = Tn s dao ng tnh bng (Hz) R1 = in tr tnh bng ohm ( ) R2 = in tr tnh bng ohm ( ) C1 = T in tnh bng Fara ( ) T = Tm + Ts Tm = 0,7 x ( R1 + R2 ) x C1 Ts = 0,7 x R2 x C1 T : chu k ton phn Tm : thi gian in mc cao Ts : thi gian in mc thp

Chu k ton phn T bao gm thi gian c in mc cao Tm v thi gian c in mc thp Ts T cc cng thc trn ta c th to ra mt dao ng xung vung c rng Tm v Ts bt k. Sau khi to ra xung c Tm v Ts ta c T = Tm + Ts v f = 1/ T * Th d bn thit k mch to xung nh hnh di y.

Mch to xung c Tm = 0,1s , Ts = 1s Bi tp : Lp mch dao ng trn vi cc thng s :

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C1 = 10F = 10 x 10-6 = 10-5 F R1 = R2 = 100K = 100 x 103 Tnh Ts v Tm = ? Tnh tn s f = ? Bi lm : Ta c Ts = 0,7 x R2 x C1 = 0,7 x 100.103 x 10-5 = 0,7 s Tm = 0,7 x ( R1 + R2 ) x C1 = = 0,7 x 200.103 x 105 = 1,4 s => T = Tm + Ts = 1,4s + 0,7s = 2,1s => f =1 / T = 1/2,1 ~ 0,5 Hz 5. Mch dao ng nght ( Blocking OSC ) Mh dao ng nght c nguyn tc hot ng kh n gin, mch c s dng rng ri trong cc b ngun xung ( switching ), mch c cu to nh sau :

Mch dao ng nght Mch dao ng nght bao gm : Bin p : Gm cun s cp 1-2 v cun hi tip 3-4, cun th cp 5-6 Transistor Q tham gia dao ng v ng vai tr l n cng xut ngt m to ra dng in bin thin qua cun s cp. Tr nh thin R1 ( l in tr mi ) R2, C2 l in tr v t in hi tip

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C hai kiu mc hi tip l hi tip dng v hi tip m, ta xt cu to v nguyn tc hot ng ca tng mch. * Mch dao ng nght hi tip m .

Mch hi tip m c cun hi tip 3-4 qun ngc chiu vi cun s cp 1-2 , v in tr mi R1 c tr s nh khong 100K , mch thng c s dng trong cc b ngun cng xut nh khong 20W tr xung Nguyn tc hot ng : Khi cp ngun, dng nh thin qua R1 kch cho n Q1 dn kh mnh, dng qua cun s cp 1-2 tng nhanh to ra t trng bin thin => cm ng sang cun hi tip, chiu m ca cun hi tip c a v chn B n Q thng qua R2, C2 lm in p chn B n Q gim < 0V => n Q lp tc chuyn sang trng thi ngt, sau khong thi gian t dng in qua R1 np vo t C2 lm p chn B n Q tng => n Q dn lp li chu k th hai => to thnh dao ng . Mch dao ng nght hi tip m c u im l dao ng nhanh, nhng c nhc im d b xc in lm hng n Q do mch thng khng s dng trong cc b ngun cng xut ln. * Mch dao ng nght hi tip dng . Mch dao ng nght hi tip dng c cun hi tip 3-4 qun thun chiu vi cun s cp 1-2, in tr mi R1 c tr s ln khong 470K V R1 c tr s ln, ln dng nh thin qua R1 ban u nh => n Q dn tng dn => sinh ra t trng bin thin cm ng ln cun hi tip => in p hi tip ly chiu dng hi tip qua R2, C2 lm n Q dn tng => v tip tc cho n khi n Q dn bo ho, Khi n Q dn bo ho, dng in qua cun 1-2

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khng i => mt in p hi tip => p chn B n Q gim nhanh v n Q lp tc chuyn sang trng thi ngt, chu k th hai lp li nh trng thi ban u v to thnh dao ng. Mch ny c u im l rt an ton dao ng t t khng b xc in, v c s dng trong cc mch ngun cng xut ln nh ngun Ti vi mu. * Xem li l thuy v cm ng in t :

Th nghim v hin tng cm ng in t trong bin p. th nghim trn ta thy rng , bng n ch lo sng trong thi im cng tc ng hoc ngt , ngha l khi dng in chy qua cun s cp bin i, trong trng hp c dng in chy qua cun s cp nhng khng i cng khng to ra in p cm trn cun th cp

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