mạch dao động đa hài

Gio trnh k thut xung 1

CHNG V: DAO NG DA HI ( Multivibrator)

Trong chng ny ta s kho st cc dng mch to xung, gi chung l dao ng a hi, nh mch bistable, Schmitt trigger, monostable, astable dng BJT, opamp ,vi mch nh thi 555 v vi mch s . 5.1: Dao ng a hi BJT : 5.1.1: Mch hai trng thi bn (bistable): Hnh 5.1 l mch bistable ghp C-B.Mch chia thnh hai v ging nhau, 21QQ cng m s, Rc phn cc C v l in tr ti;

1R to vng hi tip ti sinh ghp t cc C BJT ny sang cc B

BJT kia; BC t rt nhanh lm tng tc p ng; 2R r dng BI

v dn phn cc Q off t ngun BBV ( c th ni masse thay cho

ngun - BBV ).

Hot ng: Khi mi cp ngun cho mch, d 2 BJT hon ton ging nhau, nhng s c mt BJT dn trc, 1 BJT Hnh 5.1: Mch bistable ghp C.B dn sau.Ta gi s 1Q dn trc, dng 1CI tng lm 1CV gim,qua

BCR //1 lm 2BV gim, dn n 2Q dn yu. 2Q dn yu lm IC2 gim nn VC2 tng,hi tip ti sinh qua

R1//CB lm VB1 tng,Q1 dn mnh ..Qu trnh c th tip tc lm 1Q bo ha 2Q tt.

1Q bo ha : VVV CESCE 01

2Q off: CCCE VV 2

y l mt trng thi bn ca mch lun gi vng nh vy cho n khi c tc ng mi. By gi mun i trng thi ca mch,ta cho mt xung kch vo cc B Q1 hay cc B Q2.Gi s ta mun kch xung vo cc B Q2,do Q2 ang off,nn phi kch xung dng vo cc B Q2 chuyn Q2 sang on.Khi c xung dng kch vo B Q2 m bo sao cho VBE2V,Q2 bt u dn,IC2 tng lm VC1 gim v hi tip ti sinh qua R1// CB lm VB2 tng,Q2 dn cng mnhQu trnh c th tip tc lm Q2 bo ha,Q1 off.

2Q bo ha : VVV CESCE 02

1Q off: CCCE VV 1

y l trng thi bn th hai lun lun gi vng nhng vy cho n khi c tc ng mi. Nh vy mch lun lun mt trng thi bn 1BJT bo ha, 1BJT off cho n khi c xung kch vo

lm mch chuyn sang trng thi bn th hai BJT t tt sang bo ha v BJT t bo ha sang tt. Ta thy ch cn a xung kch ban u vo mch chuyn trng thi dn ca 1 BJT, khng cn duy tr xung kch, mch s t chuyn trng thi nh vo cc vng hi tip ti sinh ghp gia C-B cc BJT. V d 5.1: Cho mch bistable nh hnh 5.1: KRVVVV CBBCC 2,2,12,12 ,

KR 151 , )(,100 112 siQQKR c .20 Chng minh 1 BJT bo ha v BJT kia tt. Tnh cc gi

tr dng in , in p xc lp trn cc nhnh ca mch. Gii : Gi s 1Q bo ha, 2Q off, ta c mch tng ng nh hnh 5.2.

a) b) Hnh 5.2: Cc gi tr dng,p trn cc nhnh mch bistable ghp C-B

Ta chng minh 2Q off, 1Q sat. B qua ,CBOI tm 2BV h

Ct ti cc B 2Q :


2BV h = BBCES VRR

RV

RR

R

21

1

21

2

20 BCES VV h offQVVRR

RBB 2

21

1 56,11210015

15

chng minh 1Q sat, tm ,, 11 BC II v kim chng 11 BC II

11 III RCC

mAR

VVI

C

CESCCRC 45,5

2,2

12

mARR

V

RR

VVI BBBBCES 1,0

10015

12

2121

1

mAIC 35,51,045,51

431 IIIB

mARR

VVI

C

BESCC 65,02,215

8,012

1

3

I mAR

VV BBBES 13,0100

128,0

2

4

mAIB 52,013,065,01

mAImAI CB 35,54,1052,020 11

Thit k mch bistable ghp C B : Do tnh cht i xng ca mch, ch cn thit k trn mt trng thi v d 1Q sat 2Q off.

T hnh 5.3a ta tnh iu kin sat:

CS

CCC

C

CCCS

I

VR

R

VI (5.1)

CSBBBES

C

BESCCBS

I

R

VV

RR

VVIII

21

21 (5.2)

a) b)

Hnh 5.3: Thit k mch biatable ghp C-B T hnh 5.3b, tnh iu kin off :

CBOIII 34

CBOBEOffCESBBBEoff

IR

VV

R

VV

12

(5.3)

T (5.2)& (5.3) gii ra c 21,RR .

Chn 1R nh hn gi tr tnh v 2R ln hn gi tr tnh s d m bo iu kin bo ha.

Lu : BEoffV chn V1,0 i vi lai n-p-n v VVBBoff 1,0 i vi loi p-n-p. Trng hp

,0BBV chn VVBEoff .


E

C

cc

cc

N

On1

1

Bs1

BES

E

2

2 E

CC

cc

Off On

13

4

CBO

CESBES

BE off

2E

E

Kho st mch bistable ghp cc E nh hnh 5.4.

V c bn, mch bistable ghp cc E cng tng t nh mch bistable ghp C-B, tuy nhin 2 cc E ghp chung qua ER xung masse,v mch

khng cn dng ngun - BBV . ER chnh l vng hi tip ti sinh cng vi

BCR //1 trong qu trnh giao hon s nhanh chng p 1BJT sat v BJT

cn li off. Ngoi ra ER cn to 1 p dng EV m bo 1BJT off

vi 0BEoffV nn khng cn dng ngun m .

c im ca mch bistable ghp cc E so vi mch ghp B-C. Ch cn cp ngun n cng p BJT off vi 0BEoffV Hnh 5.4: Mch bistable ghp EC

Giao hon nhanh tc cao do BJT khng bo ha su C th cho mt ng xung kch vo cc E chuyn trng thi mch Mc p thp khng bng khng nn kh ghp vi tng sau hot ng giao hon Bin xung kch cao.

Thit k mch bistable ghp E chung:

a) b) c) Hnh 5.5: Thit k mch bistable ghp E chung

iu kin sat:

Q sat : NC VV , Q off CCC VV

bin thin p: NCC VVV

CS

CC

CS

CESCCEC

I

V

I

VVRR

(5.4)

CSCSBSCSES IIIII

11

CESCCCESNE VVVVVV (5.5)

CS

E

ES

EE

I

V

I

VR (5.6)

T (5.4) suy ra Rc. 21 III BS

21 R

VV

RR

VVVI EBES

C

EBESCCCS

(5.7)

iu kin off:

CBOIII 34

CBOBEoffCESEBEoff

IR

VV

R

VV

12

(5.8)

T (5.7) & (5.8) suy ra 21 & RR .


V d 5.2: Thit k mch bistable ghp E chung vi cc thng s sau: VVImAISiQVVVV BEOffCBOCSiCC 5,0,0,15,20)(,10,15

Gii : 75020

15

CS

CCEC

I

VRR

VVVVV CESCCE 5,42,01015

mAI

I CSBS 3,115

20

mAIII BSCSES 3,213,120

2203,21

8,4

ES

EE

I

VR

510530220750CR

Thit lp h phng trnh :

21 R

VV

RR

VVVI BESE

C

BESECCBS

(1)

CBOBEOffCESEBEOff

IR

VV

R

VV

22

2121

6,5

53,0

4,98,08,4

53,0

8,08,41533,1

RRRR

(2)

12

5,02,08,45,0

RR

21

6,5

53,0

4,933,1

RR

(3)

12

7,03,4

RR

Gii ra c KRKR 33,6,5 21

Tnh ton t rt nhanh

a).

Hnh 5.6: Mch tng ng tnh CB Hnh 5.6 l mch tng ng tnh t rt nhanh, n gin ta b qua cc in dung vo ra BJT. Ro l tng tr ra BJT on ( gm c RC)

Ri l tng tr vo ca BJT on ( )'bbi rR

Hnh 5.6a l mch tnh thi gian giao hon onoffQ 1

Thi hng ca mch : BB CRRCRRR 21021 //// do 20 RR Hnh 6.6b l mch tnh thi gian giao hon offonQ 2 :


Thi hng ca mch : BCBCiBCi CRRCRRRCRRRR ////////' 1121 do .2 Cii RvRRR

Thc t 2RRC nn '

Do hng s thi gian p ng ca mch cao nht ca mch

BCRR

RR

21

21

(5.9)

T cng thc trn ta c th tnh gn ng tn s cao nht maxf m mch c th p ng c.

Gi s vi thi gian ,2T mi p ng qu tt, mch bt u xc lp.

Nh vy: BCRR

RRf

21

21max

22

1

(5.10)

Thc t cn phi k n cc in dung tip gip ca BJT. Vn tnh ton chnh xc BC kh phc

tp. y ta a ra phng php tnh ton BC da trn in tch tch tr. Gi BSQ l in tch tch tr trn

cc B khi Q sat, BSI l dng BI bo ha.

Thi gian tch tr in tch mch cc B :

BS

BSB

I

Q (5.11)

Chn thi hng )//(, 21 RRRRCB bng vi thi gian tch tr B .

Suy ra BS

BSBB

I

QRC

RI

QC

BS

BSB (5.12)

Thc t gi tr BC thng c chn bng thc nghim vi chc pF trm pF.

Kch khi mch bistable (trigger) Nh phn hot ng cp, khi mun mch bistable o trng thi, ta phi cho xung kch vo

mch thay i trng thi mch. Nguyn tc kch c tm tt nh sau: C th kch OnOFF QQ hoc ,OFFOn QQ kch vo cc B hay cc E (mch EC)

Kch cc B :

NPN OFF ON OFFON

Xung Xung )(

PNP Xung )( Xung

Kch cc E ( mch )EC NPN xung

PNP xung )(

+ Kch i xng : xung kch a n c hai v ca mch cng mi thi im + Kch khng i xng : xung kch ch kch 1 v ca mch. Hnh 5.7 l cc mch kch khng i xng .

a) b) c) Hnh 5.7 Cc dng mch kch khng i xng.


t

t

t

t

t

0 V

0

1S

cc

cc ccs2 2

V

V

V

V -i R

0 V

0

1S

2

cc

cc ccs2 2

V

VVV

V

V -i R

R

R R

R

R

RV V

C

+V

QQ

1

2

2 E

1

1

C2

C1

Si

0

+

+

- -

cc

Hnh 5.8 l mch kch i xng thng dng mch bistable. Mch kch gm 1 ngun to xung v mch vi phn RC to gai, D ct b gai v thng gai )( a vo cc B BJT. Nh vy kch

mch trng thi offQon . Ta gi s satQ1 , offQ2 .

Khi satQ1 VVV CESC 01 , xem nh im (4) ni masse

v mch RC1 tr thnh mch vi phn. Gai dng b diode 1D ct

v gai m qua D1 kch cc B 1Q lm 1Q chuyn t on sang off.

Cng thi im , CCC VVoffQ 22 , nn phn cc nghch

kh su 2D , do gai m cng khng th dn qua 2D kch vo

,2BQ cc ,2BQ hon ton cch ly vi xung kch.

Tng t,khi 2Q on , 1Q off, gai m s qua 2D kch cc Hnh 5.8: Kch khi mch i xng

,2BQ lm 2Q chuyn t offon . 1Q cch ly vi xung kch.

Hnh 5.10 minh ha dng sng ti cc im 1,2,3,4 trn hnh 5.8. Thc t cc gai trn hnh 5.10 b,c rt kh thy do BJT o trng thi rt nhanh. Vi xung kch ng vo chu k Ti, dng sng ng ra cc 21 ,CC s l xung vung i xng chu k 2 Ti.

Mch bistable c ng dng trong cc mch chia i tn s, to xung vung i xng v l mch cn bn trong cc Hnh 5.9: Mch kch 1Q t offon

b trigger FF. 5.1.2: Mch Schmitt trigger: Mt dng mch bistable khc vi hot ng c bit hn cn gi l mch Schmitt trigger hnh 5.11. SV l tn hiu vo c dng bt k.Khi bin SV cn b

Q1 off,VC1=VCC v Q2 on:

220 CCSCC RIVV .

Khi bin SV tng ti gi tr 21 EVVV ,Q1 bt

u dn,VC1 gim,hi tip qua R1,R2 lm VBE2 gim dn n Q2 dn yu,IC2 gim lm IE2 gim dn n VE2 gim. iu ny dn n 1BEV tng lm 1Q dn mnh... Qu trnh Hnh 5.10: Dng sng ti cc im hnh 5.8

c th tip tc cho n khi 1Q dn hon ton v offQ2 .

1Q c th dn ch ng tng tc lm vic ca mch.

Nu li vng (loopgain) ca ton mch < 1 vic giao hon 2Q t offon s ko di nh hnh 5.12a.

mch giao hon nhanh, ta tng li vng ln ( bng cch tng Rc hay t s phn p 21,RR chng hn ). Khi li vng

bng 1 dc tng v hn ,mch chuyn trng thi tc thi. Khi cho li vng >1, dc s b o chiu nh hnh 5.12b

Khi SV tng n 1V , 2Q t offon , CCO VV , nu tng SV Hnh 5.11: Mch Schmitt trigger

na,mch vn gi trng thi nh vy. By gi gim SV v n

gi tr 12 VVVS , 2Q mi t onoff , 22 CCSCCO RIVV .

Khi VVS vi ,12 VVV mch c th hai trng

thi bn khc nhau, hoc im a, ,,2 CCO VVoffQ

hoc im c, 2Q on 22 CSCCC IRVo .Cn im b

l im khng n nh. Vng tr: Hnh 5.13 minh ha p ng ng ra o theo SV a) b)

khi li vng>1. Ta thy khi 1VVS offonQ 2 Hnh 5.12: p ng theo li vng

v 2VVS onoffQ 2 .


On Off1 2

S

EE1

2

C2

C1

C1

C1

B1

S 2

++

-

-

cc

t

t0

cc ccs2 2V -i R

V

V

V

V

V

QQQQ

cc

0

2

1

S

Off

Off On

On1

1

22

T trong mch xut hin 1 vng tr trong qu trnh giao hon c nh ngha:

21 VVVH (5.13)

trong : UTPV 1 : im kch trn (upper triggered point)

:2 LTPV im kch di (lower triggered point)

Vng tr c xc nh qua 1CR , t s phn p 21RR

Mun iu chnh vng tr, ta c th thay i 1CR , 21,RR

hoc c th thm 1E

R ni tip cc E 1Q ,hoc thm

R 2E ni tip cc E 2Q iu chnh loop gain nh s

thy trong v d 5.3. Phn tch : T hnh 5.11 ta tm biu thc tnh ., 21 VV

1) Tnh :1 UTPV onQoffQ 21 , Hnh 5.13: p ng ng ra c vng tr

p dng nh l Thevenine ti cc B 2Q :

CCC

VRRR

RV

211

2'

(5.14)

211

112 )(

RRR

RRRR

C

Cb

(5.15)

2Q c th bo ha hay ch ng

n gin cho : 22 BC II

2222 )1( BBCE IIII

p dng nh lut 2K cho vng kn mch 2BEQ Hnh 5.14: Tnh UTP

22 1' BEbBE IRRVV (5.16) EBEEE RIRIV 22 )1(

)1(

)1()'( 2

Eb

EBEE

RR

RVVV (5.17)

Suy ra: 11 VVV E (5.18)

Nu ,)1( bE RR ta n gin c:

121 ' VVVV BE (5.19)

Vi )(2 SiQ ta c : VVsatQVVBE 5,0),(7,0 122

V VV 2,0'1 (5.20)

(5.20) cho thy gi tr 1V v ,ER nhit nn vic thay BJT rt d dng !

2) Tnh offQonQLTPV 212 ,:

p dng nh l Thevenine ti cc C 1Q :

CCC

t VRRR

RRV

211

21

(5.21)

211

211 )(

RRR

RRRR

C

C

(5.22)

1121

22 CCB VV

RR

RV

(5.23)

p dng nh lut 2K cho vng kn mch BE Q2: Hnh 5.15: Tnh LTP

0)( 111 2 ECBC RIIVV (5.24)

Vi ,, 1111 BCCtC IIRIVV thay vo (5.24) vi ch V trong (5.14),ta c:

'

'

'

221

EE

t

CRR

VV

RR

VVI

(5.25)


On

Off

1

2

S

EE1

E1

C2

C1

C1

S 2

+

-

t

vi

11' EE RR (5.26)

S

ECBEEBCBESB

RRIVRIIVRIV ')( 111112 1

)'('

'212

VV

RR

RRVV

E

SEBE

(5.27)

Thc t EE RR ',1 v ES R

R

(5.27) c n gin thnh:

)'(212

VVRR

RVV

E

EBE

(5.28)

V d 5.3: Mch Schmitt trigger nh hnh 5.11 vi cc thng s : KRKRKRKRKRSiQQVV SCCCC 6,2,1,1,4,30)(,12 212121 v .3KRE

a) Tnh UTP v LTP. b) Ni tip

1ER vo 1EQ , tm 1ER trit tiu vng tr 0HV .

c) Ni tip 2ER vo 2EQ , tm 2ER 0HV .

Gii: a) Tnh UTP v LTP:

VVRRR

RV CC

C

612624

6'

211

2

KRRR

RRRR

C

Cb 3

264

)24(6)(

211

112

KRKR bE 393)130(3)1( nn:

VRR

RVVV

Eb

EBEE 2,5

3133

313)7,06(

)1(

)1()'( 2

( 2Q bo ha)

VVVV E 5,75,02,511

75,062

6

21

2

RR

R

KRRR

RRRR

C

C 67,2624

)62(4)(

211

2111

KR 267,275,0

)'(212

VVRR

RVV

E

EBE

( 1Q ch ng)

= VV 4)5,06(32

36,0

b) Tnh

1ER :

Khi thm 1ER ni tip 1EQ , mc UTP khng Hnh 5.16: RE1 lm tng LTP

thay i v khi tnh V1, onQoffQ 21 , nn khng c dng qua 1ER . 1ER ch nh hng n mc

LTP, c th l lm tng LTP khi ., 21 offQonQ 0HV , 1ER c tnh sao cho p ri trn

1ER chnh l 21 VVVH .

Ta c:

1

21

1

211

11 C

E

E

I

VV

I

VVR

mARR

VVI

E

C 08,11,32

5,06

'

'2

1


Off On1 2

S

E

E2

b

C2

C2

E2

B2S

++

-

-

cc

1off 2Sat

2

E

E2

E2

2

B2

1

C2

C2

C1

S

S

+

+

+

-

-

-

cc

1

BES

off2Sat

2

E

E1

E1

2

B2C1

1C1

C2C1

S

S

+

+

+

-

-

-

cc

KRE 5,1

08,130

11

47,51

c) Tnh 2ER :

Khi thm 2ER ni tip 2EQ , mc LTP khng nh hng, v khi tnh LTP ., 21 offQonQ

2ER ch nh hng n UTPV 1 khi onQ2 , c th l gim UTP.

Cng ging nh trn, 2ER c tnh sao cho 2ER bng 21 VVVH

p dng nh lut 2K cho vng kn mch 2BEQ :

2222 1

1)(' CEEBE

Cb IRRVI

RV

hay 222 130

1)3(8,0

30

36 CC IRI

)20,3033,1(

2,5

2

2

E

CR

I

3.30

11

)20,303,1(

2,511.

2

221

E

ECEEER

RIRIV

Hnh 5.17: 2ER lm gim VTP

=)20.303,1(

7,16

2 ER

VVVVV E 42111 0HV

121

VVVE

hay 5,35,0420.303,1

7,16

2

ER

KRE 5,12

C th thay i SR trit tiu vng tr : Khi tng SR UTPV 1 khng nh hng v khi

SRoffQ ,1 ch nh hng ti LTP khi offQ1 , c th l tng LTP. tm SR ta cho 12 VV .

Tuy nhin nu tng R1 cao qu c th lm li vng


1

CES

in

Sat

+

++

-

-

-

C

B2

cc

t

t

t

t

CES

CES

C1

BES BES

C2cc

cc

cc

C1

T

VV

V

V - V

V

0

0 0

0

T

R RC

V

+V

Q Q1Off

i

2Sat

+-

C1

B2

cc

121

212 CEB V

RR

RVVV

)( 1121

21 CCCCE RIV

RR

RVV

(5.35)

T (5.32).(5.34),(5.35) tnh c 21 ,RR

5.1.3: Mch 01 trng thi bn (Monostable) 1). Mch monostable ghp cc B-C Khi ngun n nh, mch trng thi satQ2

(do R dn dng )2BI v .1offQ CCCCESC VVVV 12 ,

y l mt trng thi bn, ch o trng thi khi ta tc

ng xung kch vo mch.Gi s kch mt xung m vo cc :2BQ Hnh 5.19: Mch monostable ghp C-B

2Q dn yu lm 2CI gim, dn n 2CV tng.Hi tip ti sinh qua

11 //CR lm 2BV tng, 1Q bt u dn, 1CI tng lm 1CV gim, hi tip ti sinh qua C lm 2BV gim v 2Q

dn cng yu... Qu trnh tip tc khi cho n khi 1Q bo ha, .2offQ

a) C np khi 1Q sat b) C x khi 2Q sat

Hnh 5.20: Qu trnh np x C Khi 1Q bo ha offQVV CESCE 21 , CCC VV 2 . Khi 1Q sat, 1CV gim t CCV xung CESV nn lm

2BV gim 1 lng nh vy dn n 2BV m. C np t ngun CCV qua R v 1CEQ theo thi hng .RC

Sau thi gian T, VVB 2 kch 2Q dn tr li v hi tip ti sinh qua CCR ,// 11 s lm mch o

trng thi .,,, 2211 CESCCCC VVsatQVVoffQ

Tuy nhin khi offQ1 , cc C 1Q s c vt l ' v qua C lm 2BV c vt l , 2Q dn vi

dng CI B ,' 2 x qua tip gip 2BEQ , masse, ngun CCV v .1CR Nh vy 1CV s tng t t ln CCV qua thi

hng .' 1CCR

Tnh thi gian mono T v vt l : Ti t=0 - , satQoffQ 21 , , in p tch trn C

BESCCAC VVVV )0(

p dng hng v cc 1CQ .

Ti ,,:0 21 offQsatQt thay mch 1CEQ bng ngun .CESV

T hnh 5.22c tm c biu thc 2BV v ch VTVB )(2

ta tm c :

VV

VVVRCT

CC

CESBESCC

2ln (5.36)

Vi gi s VVVV CESBESCC ,, n gin (5.36) thnh:

RCRCT 69,02ln (5.37)

Hnh 5.21: Cc dng sng mch monostable

hnh 5.19


+

+

+

+

-

-

-

-

cc 1

2

B2

A

CES

+

+

-

-

C1

1

2

cc

B2bb

rig C

C

R

R

R

R

R

V

R C

V

+V

Q Q1 2i

B E

C2

A

1C1

2

B

+

+

+

-

-

-

cc

T

I1 t

t

t

t

V -I RCC 1 C1

V

V

V

+

B2

E1

E2

1

1

C1

C1

C2

CC

E2

CC

C2

CES

B2

E2 BES

BE1

B2 bb

C1C1

E1

E2

E

I

I

R

R

R

V

+V

VV

V

I

V

R

+V + I r

V

V =V-V

V

V

0

0

00

Ic2

V (o-)B2

0

V

a) Khi offQ1 b) Khi satQ1 c) Mch tng ng tnh T

Hnh 5.22: Mch tng ng tnh T

Khi offQ1 c vt l ' ti cc 1CQ v qua C lm 2BV c

vt l .Ti thi im onQ2 v xut hin dng .' 2BI

Mch tng ng khi satQ2 l rbb v ngun BESV .

Do 1CRR xem nh dng 2'BI ghp qua '1 ,, bbC rCR .

T gin xung hnh 5.21, ta c:

VVrI BESbbB '2' (5.38)

CESCBCC VRIV 12'' (5.39)

Do '

2''bbC

BESCESCC

BrR

VVVVI

(5.40)

VVrR

rVVVV BES

bbC

bbBESCESCC

'

')( (5.41)

Thit k mch monostable ghp C B: Hnh 5.23: Mch tng ng tnh Thng s bit BEOffCSCC VTIV ,,,,

:2satQ CS

CESCCC

I

VVR

(5.42)

CS

BESCC

BS

BESCC

I

VV

I

VVR

)(

(5.43)

R

TC

69,0 (5.44)

21RR c xc nh tng t nh mch bistable

2). Mch monostable ghp cc E:

Hnh 5.24: mch monostable ghp cc E Trong mch hnh 5.24, hi tip ti sinh qua C v ER , xung

trigger dng a vo ,1BQ p ly ra trn .2CQ Hnh 5.25: Dng sng mch

Bnh thng satQ2 , .1offQ Khi cho xung trigger dng vo monostable ghp cc E

onQBQ 11, hi tip ti sinh qua C, ER lm 1Q dn ( c th ch ng


2

E

C2

C2

C2

B2

BES B2

+

-

cc

+

-

VCES

hoc bo ha)v offQ2 . Khi onQ1 , C np t CCV qua R v 1CEQ lm 2BV tng dn.

n thi gian T, 12 EB VVV lm onQ2 v hi tip ti sinh qua C, ER lm .1offQ satQ2 tr li.

C x dng qua tip gip BE Q2GNDVcc RC1 to dng IB2 gy ra vt l '2.' bbB rI trn cc B Q2,

ng thi to dng IE2 gy ra vt l in p ln VE2 trn cc E. Thi gian mono T c kim sot bi dng 1I c iu khin bi V l in p vo 1BQ . Thi gian

mono T t l tuyn tnh vi in p V. V d 5.4 : Mch monostable hnh 5.24 c cc thng s sau: KRKRVV CCCC 5,6,18 21

VVrSiQQKRKR bbE 5,200,50)(,4,100 '21 . Tnh cc gi tr c th trn gin xung hnh

5.25.Cho VBES=0,8V,VCES=0,2V. Gii:

t < 0: .1offQ satQ2 mch tng ng nh hnh 5.26

)( 222 BCEBESBCC IIRVRIV

22)( CEBEBESCC IRIRRVV (1)

)( 2222 BCECESCCCC IIRVIRV

222 )( BECECCESCC IRIRRVV (2)

(1),(2)

22

22

948,17

41042,17

CB

CB

II

II

Gii ra c mAImAI BC 95,0,95,1 22

VIIRV BCEE 2,8)095,095,1(4)( 222 Hnh 5.26

VVVV EBESB 92,88,022

VVVV CESEC 4,82,02,822

VVV CCC 181

VVVB 51

:0t Kch xung vo onQBQ 11, v offQ2 . Gi s 1Q dn ch ng VVBE 6,01

VVVV BEE 4,46,051

mAIIR

VBC

E

E 1,14

4,411

1

11111 CBC III

mAR

VI

E

EC 08,1

51

1,1.50

11

1

Ti :0t RC III 11 (3)

p dng 2K cho vng kn :,,1 RCRC

011 RAC RIVIR (4)

VVVVV BCAA 9918)0()0( 21 (5)

Thay (3), (4), (5), ta c:

mAII

VII

R

R

08,1

91006

1

1

Gii ra c mAImAIR 93,0,15,0 1

VVV CCC 182

VRIVV CBB 42,36.93,09)0( 1122

V VVEE 4,412

VIRVV CCCC 42,1293,0.618111

Ta c: VVVV BCCB 42,7542,12111


+

+

+ +

+

BE

CC CC

CESS

6k

1

2

2

A (T )

6,8v

C1

bb

0,2k

5k

18v

0,8v

4k

0,2v

C1

C2

18v

R RR

R>>

V

RI

I

V V

V

E

Nh vy 1Q tht s dn ch ng

t = T-: Trong thi gian mono T C np, 2BV tng theo thi hng RC

Ti t =T - : VVVV EB 9,45,04,4212

mAR

VVI BCCR 13,0

100

9,4182

mAIII RC 95,013,008,111

VRIVV CCCC 3,126.95,018111

p trn C: VVVV BCA 4,79,43,1221

t = T+: Mch tng ng ti t = T+ nh hnh 5.27. Khi t = T+ , ., 21 onQoffQ Mch tng ng 2BEQ l rbb

v ngun .BESV Ti thi im ny xut hin vt l, 2'BI

v 2'CI tng ng l dng cc B v 2CQ ti t = T+.

Gi s 1CRR , b qua dng R vit phng trnh

dng vng:

0'''

0''')('

2222

22'212

CBECESCCCC

CBEBESbbBACBCC

IIRVRIV

IIRVrITVRIV

mAImAI

II

II

CB

CB

CB

84,1',35,0'

8,17'9'4

4,10'4'2,10

22

22

22

VIIRVV CBEEE 76,8)84,135,0(4)''(' 222

VVVV CESEC 96,82,076,8' 22

VRIVV CBCCC 9,156.35,018' 121

VrbbIVVV BBESEB 63,92,0.035,8,076,8''' 222

Gii hn gi tr V: Khi offQonQ 12 , gii hn V = Vmax 1Q vn off

12max VVV E (5.45)

Khi 121 , IoffQonQ phi ln .2offQ Ta tm min1I offQ2 ,t suy ra min1EV 2Q vn off:

1min1min BEE VVV (5.46)

Ta c : 211122 )0()0( VVRIVV ECBB (5.47)

RE

EC II

R

VI

1

11

1

1122 )0()0( CBCCBCCR RIVVVVRI

R

RIVVI CBCCR

112 )0(

R

RIVVI

R

V CBCC

E

E 1121

1 )0(

1

R

VV

R

V

RR

RI BCC

E

E

C

)0(

121

1

1

(5.48)

Thay (5.48) vo (5.47)

EC

C

BCC

C

CB

E

RRR

RR

VVRR

RVV

V

)1(1

)0()0(

1

1

2

1

122

1

(5.49)

min1EV khi du ng thc xy ra.

Gi s ,1,1 CRR ta tnh gn ng (b qua in p tip gip):


+ +

++

+

CC

12

B2

B2

21

1

C(0 )

C1

C1

C(0 )

E1CC

R

R

R

L

R

1/sc

V

IV

S

S(S)

S

RR

+V

B2

t

t

t

t

0

0

V V

V

V -

V -

V

V

V

V

V V

V

V

V

V

V

ccC2

2

1

1

2

1

1

22

1

2

C1

CC

CC

CES

CES

CES

CES

BES BES

BES

B2

B1 2

T1 T2

0

0

E

CCE

R

VV

11

min1

(5.50)

Tnh rng xung mono T: Mch tng ng khi 1Q dn ch ng, offQ2 ti t=0

+ nh hnh 5.28:

E

BE

E

EEBEE

R

VV

R

VIVVV 11111 ,

)()0(),0()0(2

222 CESCC

EC

EBESEBESBBCCCA VV

RR

RVVVVVVVV

(5.51)

Dng xp chng tm c:

11

211

1

1

)0()(

ln)(

VVVV

VVVVR

R

RR

RRRCT

BECC

BCCBE

E

C

C

C (5.52)

Gi s ,1,1 CRR b qua cc in p tip gip:

K

RR

RK

R

R

RCT CE

E

E

C

1

1

ln 2

1

(5.53)

CCV

VK

T y c th kho st T(K) tm K cho mch hot ng monostable.

5.14: Mch Astable (khng trng thi bn) 1). Mch astable ghp C-B:

Hnh 5.29: Mch Astable ghp C-B Hnh 5.30: Dng sng cc cc B,C hnh 5.29


1 2

1

P

21

C2C1 2

cc

+

1 2

12

21

C2C1

cc

Gi s CCCCESC VVVVoffQsatQ 2121 ,,, 1C np t CCV qua R1 v 1CEQ lm 2BV tng theo thi

hng .111 CR Sau thi gian 1T VVB 2 lm onQ2 , hi tip ti sinh qua C2 v C1lm Q1 off ,Q2 sat,

CCC VV 1 , CESC VV 2 . Khi ,2satQ 1C x qua 2BEQ v GND,ngun CCV v 1CR to dng 2'BI v vt l

1 cc 2BQ v 1CQ .Sau dng 2BI gim theo thi hng 2111 ,' BC VCR gim theo 1' v BESV v 1CV

tng n CCV theo 1' . ng thi ,2satQ 1BV t bin m mt lng CESCC VV , 2C np t CCV qua 2R v

2CEQ theo thi hng .222 CR Sau thi gian 12 , BVT t n V lm 1Q on tr li, hi tip ti sinh qua

21 ,CC lm ., 21 offQsatQ

Khi 21 ,CsatQ x qua 1BEQ v GND,ngun CCV v 2CR , to dng 1'BI v vt l 2 cc B Q1

v C Q2.Sau , 1BI gim theo thi hng 222' CRC , 1BV gim v BESV v 2CV tng ln CCV theo 2' .Cng

thi im satQ1 , 2BV t bin m mt lng CESCC VV , 1C li np t ngun CCV qua R1 v CE Q1... Qu

trnh c th tip tc v ta c chui xung vung cc ng ra C Q1 v CQ2. Thi gian 21 ,TT , vt 21, c tnh tng t nh mch monostable ghp C B.

Cng thc gn ng tnh chu k dao ng: 221121 69,069,0 CRCRTTT (5.54)

Phng php iu chnh f : Hnh 5. 31 minh ha cc phng php iu chnh f cho mch astable.

a) iu chnh bng bin tr b) iu chnh bng ngun p Hnh 5.31: Cc phng php iu chnh f

Phng php ci thin cnh xung:

Nh phn tch trn, khi 1 BJT off, cc C khng t bin ngay t CCCES VV m do nh hng ca C x qua Rc nn in p

tng dn ln CCV , lm cnh xung b mo.

Xem hnh 5.32, gi s khi 11 ,DonQ dn xem nh ni tt,

in tr cc 1CQ , 111 ''//' CCC RRR , mch vn ging nh hnh 5.29.

Khi Q1 off,VC1 tng t bin ln CCV lm offD1 cch ly 1CQ khi

nhnh 11.CC x qua 2BEQ v GND,ngun Vcc v RC1. Do cnh

xung c ci thin. Hnh 5.32: Ci thin cnh xung ng ra 2). Mch astable ghp cc E: Mch monostable ghp cc E c th chuyn sang hot ng ch astable. Khi ta chnh maxVV ,

trng thi Q sat2 , offQ1 s chuyn thnh onQ1 ( dn ch ng) v hi tip ti sinh qua C, ER lm

onQ1 , offQ2 .

Khi onQ1 , offQ2 C np t CCV qua R v ERCEQ ,1 . Sau thi gian 1T bng thi gian mono xc

nh (5.52), 2BV t n 2V , onQ2 v hi tip ti sinh lm satQ2 , offQ1 . Khi satQ2 C x qua ERBEQ ,2 ,

GND, ngun CCV v 21 , BC VR gim theo CRR EC )( 12 v sau thi gian 2T , 12 VVVV BESB hay


1 2

E

C21

P

C1

2

+

+ -

-

cc

R

E1 1

1

1

2

2

BE-

E2=

E1

B2B2

E

B2 BES

1

1

2

E

V =V

T

V V

V

V =V+V -

T

V

V

V +

V

V

V

V

V-

t

t

+

+

+BE

CC

E2 C2 B2 S

1 2

2

CC1

bb

R R

V

R

V

I =I +I

+

+

+BE

CC

S

1 2

C (T )1C1

bb

R R

V

R

V

2

2

BES

B2

g

T

T

V

V

V

T T

12 VVVE lm onQ1 tr li, hi tip ti sinh s p onQ1 , offQ2 ... Qu trnh c th tip tc lm xut hin

chui xung vung ng ra C 2Q .

a) Mch astable ghp cc E b) Dng sng ti cc B v 2EQ

Hnh 5.33: Mch astable ghp cc E v dng sng Tnh chu k dao ng: TTTTT 121 , : thi gian mono (5.52)

Tnh 2T theo mch tng ng hnh (5.34)

Hnh 5.34 Phn nh ER v mch B

Gi s BESCCbbEC VVrRRR ,)1(, '1

Tnh gn ng:

1

1

1

12

)(

)1(

)1(ln)1(

VVV

TVV

RR

RRRT

BES

CCC

CE

EEC (5.55)

vi )()()()()( 121112111 ECCCBCC VVRIVTVTVTV

Kch khi mnh astable: Nguyn tc kch khi mch astable cng ging nh trigger mch

bistable, monostable.Gi s ta kch offQ2 on.Trong thi gian off, 2BV

tng n V trong thi gian 2T , 2Q mi on li, ta gi l dao ng t do.

Khi cho xung kch dng vo cc 2B vi bin v tn s thch

hp, bin xung chng ln bin 2BV .Theo hnh 5.35,ta thy ti xung

kch th 4, VVB 2 lm onQ2 tr li.Thi gian off 2Q gim xung cn

gTT 4'2 .Gi s khi offQ1 ,a xung kch dng vo 1Q cng ging nh Hnh 5.35: Kch mch astable

vy,ta c mch astable c ng b xung kch v cho xung ra fgfo 4/1 .

5.2: Dao ng a hi dng OPAMP:


++

+ +

+

++

+

+

t

t

f

t

C

Vi+

+V =V0(0 ) CC

+

+R

VCC

+

B

1

CC

CC

CC2 0+

+++

5.2.1: Mch monostable :

a) Mch monostable b) C np c) C x

Hnh 5.36: Mch monostable OPAMP v cc ng np x

Ti 0t : mch n nh, CCCCii VVRR

RVV

21

2,0 ,nn CCi VVV 00 .

CCC VV )0( cc tnh nh hnh 5.36b.

Ti 0t : xung kch m lm CCii VVVV

0,00 nn Vi+ tng vt ln CCV2

CCC VV )0( .

Sau C np theo chiu nh hnh 5.36b theo thi hng ViRC, gim theo .

Hnh 5.38: Mch tng ng tnh T

Ti t= T-: 0)( iCC VVTVi , ng ra o rng thi CCVV 0 , Vi+ t bin m mt lng

CCV2 gi CV khng i .Sau C x theo chiu nh hnh 5.36c theo RC .

gim thi gian x t sau thi gian mono T, cn gi l thi gian hi phc, ta mc thm diode D//R. Khi CCVV 0 ,kt thc thi gian mono T,Vi

+ t bin m CCV2 lm D on tng ng in tr fR , C

x nhanh qua D theo CR f' lm Vi+ t bin v 0 nhanh chng.

Tnh T: Mch tng ng nh hnh 5.38:

Cc iu kin : CCC VV )0( chiu nh hnh

CCVV )0(0

CCVTVi )( (5.54)

Tm c:

2

ln2

ln RCT (5.55)

5.2.2: Mch Astable:

Gi s CCVV 0 , 21

2,RR

RVVi CC

C np t Vo qua R, iV tng theo thi hng RC

Ti

1Tt : CCi VTV )( 1 lm 0 iV , CCiCC VVVV

,0


1

R

i

12

CC

CC

0++

+

+

R

Vi+

V =V0 CC

+

-+

CC(0+)

CC

CC 1

2CC

0++

+

21

CC

CC

CC

CC

0

0i

i

0

C x qua R vo ng ra OPAMP v GND, iV gim theo RC

Ti 21 TTt : CCi VTTV )( 21 lm 0 iV , CCiCC VVVV

,0

Qu trnh c th tip tc...

a) Mch astable b) Dng sng

Hnh 5.39: Mch astable OPAMP v dng sng Tnh chu k dao ng T:

Chu k dao ng T =T1+T2 -Tnh 1T : mch tng ng nh hnh 5.40.

Chn gc thi gian ti u T1.Ta c:

CCC VV )0( v CCVV

)0(0

Tm c:

1

1ln1 RCT (5.56a)

-Tnh T2: mch tng ng vn nh hnh 5.40 Chn gc thi gian ti u T2.Ta c:

CCC VV )0( v CCVV

)0(0 ,cc tnh ngun

)0( CV v )0(0V ngc chiu so vi hnh 5.40 Hnh 5.40: Mch tng ng tnh T

Tm c:

1

1ln2 RCT (5.56b)

Chu k

1

1ln221 RCTTT (5.57)

Nu chn 2

121 RR

Suy ra : 3ln2RCT (5.58)

5.2.3: Mch Schmitt trigger : Gi s Vi b nn CCi VVV 0,0

Hi tip dng v lm Vi+ c gi tr:

21

12)1(RR

VRVRUTPVi CCR

(5.59)

Khi Vi tng n UTP lm CCi VVV 00

Lc ny Vi+ c gi tr :

21

12)0(RR

VRVRLTPVi CCR

(5.60)

Gim Vi n LTP lm CCi VVV 00

rng vng tr:

CCH VRR

RLTPUTPV 2

21

1

(5.61) Hnh 5.41: Mch Schmitt-trigger

t RCC

H Vn

VVnRR

1

212 (5.62)


+

+

CC

11

0+

+

t

t

t

CC

CC

0

C

0

0

0

2/3

00

0

1/3Vcc

5.3: Vi mch nh thi 555 Hnh 5.42 m t cu trc vi mch 555 gm 2 mch so snh CMP1, CMP2, in p chun TLTH VV , ly t nhnh ba in tr R.

Ngng so snh CMP1 CCTH VV3

2 v ngng so snh CMP2

CCTL VV3

1 . Mt RS FF nhn tn hiu so snh t 2 ng R,Sv cho

tn hiu ra Q l ng ra. Ng _

Qdng li Q0 lm vic on/off nh

mt kha x t ngoi mc vo chn 7. M t chc nng s chn:

Chn 8: CCV cp ngun

Chn 1: GND Masse Chn 2: Trigger ng vo )( CMP2, s dng lm ng Hnh 5.42: Cu trc vi mch 555

to xung kch )( , tc ng khi bin TLCC VV 3

1.

Chn 6: Threshold ng vo(+) CMP1,ng vo ngng o trng thi tc ng khi

bin THCC VV 3

2.

Chn 7: Discharge kt ni vi cc C Q0, s dng lm ng ra x t. Chn 3: OUT ng ra xung vung

Chn 4: RES ng vo reset FF, tc ng mc 0, lm ng ra chn 3 =0. Chn 5: Voltage control ng vo iu ch tn s bng in p thay i mc ngng THV .

Tm tt mt s thng s k thut vi mch 555 Cp ngun: V183

Ng ra: mc V00 , mc CCV1 , kh nng cp/ nhn dng

Dng ng ra max: 200mA Tn s lm vic : fmax=100kHz, xung mono min s10 .

5.3.1: Mch monostable a) Mch monostable b) Dng sng Hnh 5.43: Mch monostable vi mch 555 v dng sng

Mch monostable tiu biu nh hnh 5.43a.C0.01MF chn 5 n nh p chn 5.

Khi mi cp ngun, mch reset 11CR gi mc 0 ban u reset FF lm ng ra Q= V0=0,ng ra 1Q

lm onQ2 gi chn 7 mc 0, lm C khng np, 0CV .

0CV lm ng ra CMP1=0,dn n R=0.Ng trigger chn 2 CCV3

1 lm ng ra CMP2 = 1,dn n

S=0.Nh vy ng ra FF vn gi trng thi ban u 0Q , 1Q ,mch trng thi bn.

Ti t=0+: Kch mt xung m vo chn 2 sao cho in p ti chn 2 CCV3

1 .Ng ra CMP2 =1 ,dn n

S=1,R=0,FF lt trng thi 1Q , 0Q ,Q0 off,V0=VCC ,C np t ngun CCV qua R theo .RC Trong thi

gian C np,xung trigger kt thc,in p trn chn 2>1/3VCC,in p trn chn 6


DD

i 0

DD1

i 0

2

D

P

CC

1

2

0

+ V

V V

V

1/3 2/3

V

cc

cc

cc

C

0

12

0

0

t

t

FF duy tr trng thi trc 1Q , 0Q ,Q0 off,V0=VCC.

Ti t = T-: Vc t n 2/3 VCC lm ng ra CMP1 = 1.Lc ny ng vo trigger chn 2 tr v mc 1- >

ng ra CMP2 = 0.Nh vy R = 1, 0S lm FF lt trng thi, 1,00 0 QVQ lm onQ0 ,C x nhanh

qua Qo, VC nhanh chng gim v 0 -> ng ra CMP2 = 0 -> S = 0, R =0 , FF n nh trng thi ban u.

Tnh T: lu 0)0( CV v CCC VTV3

2)(

Tm c T=1,1RC (5.63) 5.3.2: Mch Astable:

Gi s ng ra mc cao CCVV 0 , tng ng FF c trng thi Q = 1, offQQ O,0 , C np t ngun

CCV qua R1 v R2 theo CRR )( 211 .Sau thi gian 1T VC t n 2/3 CCV lm ng ra CMP1 = 0, ng ra

CMP2 =1, R = 1, S = 0, FF lt trng thi Q =0 00 V 01 QQ on,C x qua R2 vo chn 7 qua Q0

xung GND theo CR22 .Sau thi gian T2,VC t n 1/3 VCC lm ng ra CMP2=1,ng ra CMP1=0,dn

n R=0,S=1,FF lt trng thi Q =1 10 V 00 QQ tt ,C li tip t np

a) Mch astable b) Dng sng Hnh 5.44: Mch astable vi mch 555 v dng sng

Tnh chu k T: 21 TTT

Thi gian :1T CCC VV3

1)0( C np qua 21 RR

Thi gian 2T CCC VV3

2)0( C x qua 1R v masse

Tm c : CRRCRT )(69,069,0 212 (5.64)

Chn 21 RR : CRT 238,1 (5.65)

Trn y l hai mch c bn dao ng a hi s dng vi mch nh thi 555. Ngoi ra da vo cu trc vi mch 555, ta c th thit k rt nhiu dng mch to xung khc nhau, trong mch iu ch FM hay rng xung da vo in p a vo chn 5.

5.4: Dao ng da hi dng cng logic

Cc cng logic nh CMOS rt d s dng lm mch dao ng a hi. Ta xem cu trc c bn cng NOT nh hnh 5.66 b

a) b) c) Hnh 5.66: Cu trc c bn v c tnh truyn t cng NOT


t

t

t

t

31

DDDD

021

t

t

t1 2

DD

DD

O

3

2

T

0

0

0

0

1 2

DD

i

0

+

Khi in p vo Vi vt qua gi tr ngng 2/DDT VV ng ra o trng thi. Ta xem ngng

2/DDT VV l ngng o trng thi ca cng.

5.4.1: Mch monostable : Gi s 1,1,0 21 VVVi lm 00 V .

Ti t = 0+: Kch 1 xung dng vo 0, 1 VVi lm 02 V gi 0CV nh ban u. 02 V lm

10 V hi tip v ng vo cng 1 gi 11 V d xung kch mt. Lc ny C np t DDV qua R v ng ra

cng 1. 2V tng theo RC .

Ti t = T-: 2V t n TV lm 00 V , hi tip v ng vo cng 1 lm 11 V , gi Vc khng i 2V

vt ln gi tr TV DDV . Tuy nhin do ng vo cng 2 c diode bo v nn xn gi tr DDVV 2 . C x qua

diode bo v ng vo cng 2, qua ngun DDV v ng ra cng 1.

a) Mch monostable b) Dng sng

Hnh 5.67: Mch monostable cng logic v dng sng

Thi gian mono : TDD

DD

VV

VRCT

ln (5.66)

RCRCTV

V DDT 69,02ln2

(5.67)

5.4.2: Mch Astable

a) Mch Astable Hnh 5.68: Mch astable cng logic v dng sng b) Dng sng

Ti t = 0, 0,1 02 VV ,C np t DDVV 2 qua R v ng ra 0V v GND theo RC , 3V tng dn

theo v qua 1R lm 1V tng theo. Cho n khi TVVV 13 , qua cng 1 lm 02 V , qua cng 2 lm

10 V . p trn C khng thay i, 3V phi tng n gi tr TDD VV . Sau C x qua R vo ng ra 2V

cng 1 theo RC , 3V gim ko theo 1V gim n TV cng 1 o trng thi, 12 V lm 00 V tr li.

p trn C khng thay i, 3V phi gim n gi tr DDT VV . Qu trnh c th tip tc...


Tnh chu k T: 21 TTT

Tm c

TDD

TDD

T

TDD

VV

VV

V

VVRCT

2ln (5.68)

RCTV

V DDT 2,22

(5.69)

Trong thc t mi cng logoc c TV khc nhau nn cc biu thc trn ch l gn ng! Nu 3V kt

ni trc tip qua V1, diode bo v ng vo cng 1 s kp gi tr t nn ta cch ly 1V v 3V bng RR 1 .

Bi tp chng V

5.1: Kim chng li cc biu thc tnh thi gian mono T, chu k dao ng T: a) Mch monostable ghp C-B b) Mch astable ghp C- B

5.2: Kim chng li cc biu thc tnh thi gian mono T, chu k dao ng T mch astable ghp EC. 5.3: Kim chng li cc biu thc tnh thi gain mono T, chu k dao ng T: a) Mch monotable OPAMP b) Mch astable OPAMP 5.4: Lp li 5.3 vi cng logic. 5.5: Mch bistable ghp C- B c cc thng s: VVSiQVVV CESBBCC 2,0),(,6 ,

.27,7,4,2,1,25@10,7,0 21 KRKRKRCtnAIVV CCBOBES

a) Tm min v chng t rng BJT1 off v BJT kia sat.

b) Tm nhit cc i mch vn hot ng ng

c) Gn thm ti LR vo cc C 1 BJT v GND, tm gi tr ti thiu minLR mch vn hot

ng ng 5.6: Mch bistable ghp C-B. CM rng 1 BJT off v BJT kia bo ha phi tha mn cc iu

kin sau: BESCBOBBCES VRRIRRVRVR )( 212112

v

21

2

21 RR

RIVV

R

VV

R

VV

RR

RIVV CBOCESBB

C

CESCCBESBB

C

CCBOBESCC

5.7: Mch bistable ghp EC cc thng s : VVVVSiQVV CESBESCC 2,0,7,0),(,6 ,

.430,20,1,30min 2 EC RKRKR

a) Tm gi tr dng v p trn cc nhnh ca mch b) Gn thm ti LR vo cc C v GND ca 1 BJT, tm minLR mch vn hot ng ng.

5.8: Mch Schmitt trigger c cc thng s : KRKRKRVV CCCC 2,1,4,12 121

.30)(,1,3,62 SiQKRKRKR BE

a) Tm 1CI v 1BI khi UTPVi 1 , cho bit Q dn bo ha hay ch ng.

b) Lp li cu a khi LTPVi 2

c) Nu tng KRC 42 ,chng minh rng 2Q dn bo ha, offQ1 . Tm gi tr 22 BC vII .

5.9: Thit k mch Schmitt trigger dng BJT Si c 80min .Chn VVCC 30 ,

KR 241 , KR 62 . Yu cu UTP = 4,5V, LTP = 1,5V, chnh lch p tt/ dn ng ra l 10V,

2Q hot ng ch ng .Tm .,, 21 ECC RRR

5.10: Mch monostable ghp C- B c in tr R ni n ngun CCVV . K n nh hng ca

BCOI , chng minh rng xung mono T cho bi biu thc.

VRIV

RCIVVVRIVT

CBO

CBOBESCESCCCBO

ln


CC

12

0+

+VCC

CC

12

0+

+VCC

CCE

0

+

Z

CC

1

2

0

5.11: gim thi gian hi phc ca mch monostable ( thi gian t lc xut hin vt l n khi 2BV tr v BESV ), ngi ta mc thm diode zener cc C ca 1Q v GND . Nu

22

CCVV , chng minh T = 0,41 RC.

5.12: Mch monostable ghp C- B cc thng s: )(,3,12 SiQVVVV BBCC ,30

.1000,200,20,2 '21 pFCrKRRKR bbC B qua BCOI .

a) V dng sng ng ra cc B v cc C 2BJT, ch thch cc gi tr c bit. b) Tm rng xung mono T.

5.13: Thit k mch monostable ghp C-B, b qua I CBO , BJT c 20min . trng thi bn,

offQ1 vi VVB 11 v satQ2 vi dng BSI gp i dng BI ti thiu duy tr satQ2 .

Cho 21 CC RR , msTmAIIVV SCSCCC 3,2,12 21 .

5.14: Mch astable ghp C-B, 21vRR cng ni tip n ngun CCVV . Tm biu thc tnh

chu k dao ng. 5.15: Mch astable ghp C-B c cc thng s: ,200,40)(,6 ' bbCC rSiQVV

.50,6,5,560 212121 pFCCKRRRR CC

a) V dng sng ti cc cc B,C, ch thch cc gi tr c bit. b) Tnh chu k dao ng c) Thi gian hi phc rt ( thi gian t lc 2'BI bng 90% ->10% gi tr cc i)

5.16: Mch monostable dng OPAMP: a) Tnh thi gian Vi+ tr v khng sau khi kt thc xung mono hay thi gian hi phc rt

( thi gian t 90% -> 10% gi tr tuyt i ) b) Lp li cu a khi mc thm diode, xem diode dn tng ng vVR f .

5.17: Ni thm ngun V vo chn R ( thay v R ni GND) mch monostable OPAMP hnh 5.36a. Tnh T ?

5.18: Mch astable OPAMP c ngun +V phn cc Vi+ nh hnh 5.18. Tnh chu k dao ng . 5.19: Mch astable nh hnh BT 5.19 c D// C (gi s D l tng). Hy cho nhn xt v hot ng

mch.Tnh cc rng xung? Hnh BT 5.18 Hnh BT 5.19 5.20: Mch monostable nh hnh 5.20. Tm biu thc tnh T. 5.21: Mch VCO nh hnh BT 5.21. Tm biu thc tnh chu k dao ng, gi s R bng vi gi tr

R trong nhnh 3R trong cu trc vi mch.

Hnh BT 5.20 Hnh BT 5.21

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