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MC LCTrang
M u
Phn I: C S L THUYT
I. Khi nim chung v ngun mt chiu
II. Bin p v chnh lu
III. Lc cc thnh phn xoay chiu ca dng in ra ti
IV. n nh in p
Phn II: THIT K NGUN MT CHIU N P C IN P RA
THAY I (0 15V) 3A
I. S khi ca khi ngun
II. La chn phng n thit k
Phn III: TNH TON CC THNG S K THUT V LP RP
MCH THC T
I. Tnh ton thng s cho tng khi mch
II. Lp rp mch thc t
Kt lun
Ti liu tham kho
M u
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Ngy nay cng vi s tin b ca khoa hc v cng ngh, cc thit b in t
ang v s c ng dng ngy cng rng ri trong hu ht trong cc lnh vc kinh t
- x hi cng nh trong i sng. Trong tt c cc thit b in t vn ngun cung
cp l mt trong nhng vn quan trng nht quyt nh n s lm vic n nh
ca h thng. Hu ht cc thit b in t u s dng cc ngun in mt chiu
c n p vi chnh xc v n nh cao. Hin nay k thut ch to cc ngun
in n p cng ang l mt kha cnh ang c nghin cu pht trin vi mc ch
to ra cc khi ngun c cng sut ln, n nh, chnh xc cao, kch thc nh
(cc ngun xung).
T tm quan trng trong ng dng thc t ca ngun in mt chiu n p v
da vo nhng kin thc c hc cng nh t tm hiu, em chn ti: Thit
k mch ngun mt chiu n p c in p ra thay i (0 15V) 3A qua
tm hiu k hn v nguyn l hot ng ca cc mch ngun ng thi cng c thm
k nng trong thit k cc mch in tng t.
Trong qu trnh thc hin ti em xin chn thnh cm n thy gio: Th.s V nh
Tng tn tnh hng dn gip em hon thnh ti ny.
Do kh nng kin thc bn thn cn hn ch, ti chc chn s khng trnh nhng
thiu st, em rt mong nhn c s ng gp kin ca cc thy c v cc bn ti c hon thin hn.
Sinh vin thc hin
Trng Vn Quyt
PHN I:
C S L THUYT
I. KHI NIM CHUNG V NGUN MT CHIU
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 2
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Ngun mt chiu c nhim v cung cp nng lng mt chiu cho cc mch
v cc thit b in t hot ng. Nng lng mt chiu ca n tng qut c ly t
ngun xoay chiu ca li in thng qua mt qu trnh bin i c thc hin
trong ngun mt chiu.
Yu cu i vi loi ngun ny l in p ra t ph thuc vo in p mng,
ca ti v nhit . t c yu cu cn phi dng cc mch n nh (n p,
n dng). Cc mch cp ngun c in thng dng bin p, nn kch thc v trng
lng ca n kh ln. Ngy nay ngi ta c xu hng dng cc mch cp ngun
khng c bin p.
S khi ca mt b ngun hon chnh c biu din nh sau:
Hnh 1.1: S khi ca mt b ngun hon chnh
Chc nng ca cc khi nh sau:
- Bin p bin i in p xoay chiu U1 thnh in p xoay chiu U2 c
gi tr thch hp vi yu cu. Trong mt s trng hp c th dng trc tip U1 m
khng cn bin p.
- Mch chnh lu c nhim v chuyn in p xoay chiu U2 thnh in pmt chiu khng bng phng UT (c gi tr thay i nhp nh). S thay i ny ph
thuc vo tng dng mch chnh lu.
- B lc c nhim v san bng in p mt chiu dp mch UT thnh in p
mt chiu UO1 t nhp nh hn.
- B n p mt chiu (n dng) c nhim v n nh in p (dng in)
u ra ca n UO2 (IT) khi UO1 thay i theo s mt n nh ca UO1 hay IT . Trong
nhiu trng hp nu khng c yu cu cao th khng cn b n p hay n dng mt
chiu.
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A
Bin pMch chnh
l-u B lc
n p mtchiu
(n dng)
U1~ U
2~ U
TU
O1U
O2
IT
RT
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Ty theo iu kin v yu cu c th m b chnh lu c th mc theo nhng
s khc nhau v dng cc van chnh khc nhau. B chnh lu cng sut va v ln
thng dng mch chnh lu ba pha. Di y chng ta s i kho st tng khi nu
trn trong b ngun mt chiu.
II. BIN P NGUN V CHNH LU
1. Bin p ngun
Bin p ngun lm nhim v bin i in p xoay chiu ca mng in thnh in
p xoay chiu c tr s cn thit i vi mch chnh lu v ngn cch mch chnh lu
vi mng in xoay chiu v mt chiu:
Hnh 1.2: Bin p ngun2. Chnh lu
Cc phn t tch cc dng chnh lu l cc phn t c c tuyn Volt -
Ampe khng i xng sao cho dng in i qua n ch i qua n ch i qua mt
chiu. Ngi ta thng dng chnh lu Silic, c cng sut nh hoc trung bnh
cng c th dng chnh lu Selen. c cng sut ra ln (>100W) v c th iu
chnh in p ra ty , ngi ta dng Thyristor chnh lu.
Cc s chnh lu thng gp l chnh lu na chu k, s chnh lu haina chu k, s chnh lu cu m trong s chnh lu cu c nhiu u im
hn c.
Mch chnh lu phi c hiu sut (t s gia cng sut ra v cng sut hu
ch u vo) cao, t ph thuc vo ti v gn sng ca in p ra nh.
Sau y ta s xt v s chnh lu hai na chu k v s chnh lu cu.
a. Mch chnh lu hai na chu k:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 4
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c im ca mch chnh lu hai na chu k l trong c hai na chu k ca
in p xoay chiu u c dng in chy qua ti. C hai loi s chnh lu hai na
chu k: s cn bng v s cu.
D1
D2
Ct R
Ur
Uv
a. S cn bng
b. th thi gian ca in p ra
Hnh 1.3: Mch chnh lu hai na chu k
in p cc i khi khng ti: nUUU = 2
Trong Un l in p ngng ca diode, U2 in p trn cun th cp ca
bin p.
in p ngc t ln diode (trong trng hp C t 0): Ung = 2 U2hd.
b. Mch chnh lu cu:
S cu thng c dng trong trng hp in p xoay chiu tng i ln. Tuy
cng l s chnh lu hai na chu k nhng n u vit hn s cn bng ch
cun th cp c s dng ton b trong hai na chu k ca in p vo v in p
ngc t ln it trong trng hp ny ch bng mt na in p ngc t ln
trong s cn bng. in p ra cc i khi khng ti: nr UUU = 2 2 ngha l nh
hn cht t so vi in p ra trong s cn bng, v y lun lun c hai it mc
ni tip.
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A
Ur
0 t
Khng c Ct
C Ct
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C t RU rUv
Hnh 1.4: Mch chnh lu cu
Ta thy rng trong tng na chu k ca in p th cp 2U , mt cp it c
ant dng nht v katt m nht m, cho dng mt chiu qua tR , cp it cn li
kha v chu mt in p ngc cc i bng bin mU2 . V d tng ng vi nachu k dng ca 2U , cp it 13 m, 24 kha. R rng in p ngc t ln
van lc kha c gi tr bng mt na so vi trng hp s chnh lu cn bng
xt trn, y l u im quan trng nht ca s cu. Ngoi ra, kt cu th cp ca
bin p ngun n gin hn.
Trong s 1.4, nu ni t im gia bin p v mc thm ti ta c mch
chnh lu c in p ra hai cc tnh. y thc cht l hai mch chnh lu cn bng.
Ct R
+Ur
Uv
Ct R
-Ur
Hnh 1.5: Chnh lu in p ra hai cc tnh
III. LC CC THNH PHN XOAY CHIU CA DNG IN RA TI
Trong cc mch chnh lu ni trn in p hay dng in ra ti tuy c cc tnh
khng i, nhng cc gi tr ca chng thay i theo thi gian mt cch chu k, gi
l s p mch (gn sng) ca in p hay dng in sau chnh lu.Mt cch tng qut khi ti thun tr, dng in tng hp ra ti l:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 6
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=
=
++=11
0 cossinn
nn
nt tnBtnAIi
Trong 0I l thnh phn mt chiu v
=
=
+11
cossinn
nn
n tnBtnA l tng
cc sng hi xoay chiu c gi tr, pha v tn s khc nhau ph thuc v loi mchchnh lu. Vn t ra l phi lc cc thnh phn sng hi ny cho ti t p
mch, v cc sng hi gy s tiu th nng lng v ch v gy s nhiu lon cho s
lm vic ca ti.
Trong mch chnh lu hai na chu k thnh phn mt chiu 0I tng gp i
so vi mch chnh lu na chu k, thnh phn sng hi c bn (n=1) b trit tiu, ch
cn cc sng hi bc t n = 2 tr ln. V vy mch chnh lu hai na chu k c tc
dng lc bt sng hi.
Ngi ta nh ngha h s p mch KP ca b lc:
KP cng nh th cht lng ca b lc cng cao.
Ngi ta tnh ton rng khi chnh lu na chu k KP = 1,58, khi chnh lu
hai na chu k KP = 0,667.
thc hin nhim v lc ni trn, cc b lc sau y thng c dng:
1. Lc bng t in
Trng hp ny c nu ra trong trng hp ti in dung ca mch
chnh lu. Nh c t ni song song vi ti, in p ra ti t nhp nh hn.
C Rt Ur
Hnh 1.6: Lc bng t in
Do s phng v np t qua cc 1/2 chu k v do cc sng hi c r qua
mch C xung im chung, dng in ra ti ch cn thnh phn mt chiu v mt
lng nh sng hi bc thp. Vic tnh ton h s p mch ca b lc dn ti ktqu:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A
Kp
=Bin sng hi ln nht ca i
t(hay u
t)
Gi tr trung bnh ca it(hay u
t)
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tP CR
K
2=
Ngha l tc dng lc cng r rt khi C v Rt cng ln (Rt tiu th dng in
nh). Vi b chnh lu dng in cng nghip (tn s 50Hz hay 60Hz), gi tr ca t
C thng c gi tr t vi F n vi nghn F (t ha).
2. Lc bng cun cm L
Mch lc bng cun cm L c biu din nh sau
Rt Ur
L
Hnh 1.7: Lc bng cun cm
Cun cm L c mc ni tip vi ti Rt nn khi dng in it ra ti bin thin
p mch, trong cun L s xut hin sc in ng t cm chng li. Do lm
gim cc sng hi (nht l cc sng hi bc cao). V mt in khng, cc sng hi
bc n c tn s cng cao s b cun cm L chn cng nhiu. Do dng in ra ti
ch c thnh phn mt chiu 0I v mt lng nh sng hi. chnh l tc dng lcca cun L.
H s p mch ca b lc dng cun L l:L
RK tP
3=
Ngha l tc dng lc ca cun L cng tng khi Rt cng nh (ti tiu th dng
in ln). V vy b lc ny thch hp vi mch chnh lu cng sut va v ln. Gi
tr ca cun cm L cng ln th tc dng cng tng, tuy nhin cng khng nn dng L
qu ln, v khi in tr mt chiu ca cun L ln, st p mt chiu trn n tng vhiu sut ca b chnh lu gim.
3. B lc hnh L ngc v hnh
Cc b lc ny s dng tng hp tc dng ca cun cm L v t C lc, do
cc sng hi cng gim nh v dng in ra ti (hay in p trn ti) cng t nhp
nh. tng tc dng lc c th mc ni tip 2 hay 3 mt lc hnh vi nhau. Khi
dng in v in p ra ti gn nh bng phng hon ton.
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 8
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Rt Ur
L
C
Hnh 1.8: Lc hnh L ngc
Rt Ur
L
C1 C2
Hnh 1.9: Lc hnh
Trong mt s trng hp tit kim v gim kch thc, trng lng ca b
lc ta c th thay cun cm L bng R trong mt lc hnh L ngc hay hnh . Lc
R gy st p c thnh phn mt chiu trn n dn ti hiu sut v cht lng ca
b lc thp hn dng cun L. Thng ngi ta chn gi tr R st p mt chiu trn
n bng (10 - 20)%U0 khong vi n vi k .
4. B lc cng hng
Hnh 1.10.a biu din b lc cng hng dng mch cng hng song song
LkCk mc ni tip vi ti Rt nh vy s chn sng hi c tn s bng tn s cng
hng ca n. Ngoi ra t C1 cn c tc dng lc thm.
Rt
L
CkC2
Rt
Lk
Ck
L
(a) (b)Hnh 1.10: Cc b lc cng hng
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 9
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Hnh 1.10.b biu din b lc cng hng dng mch cng hng ni tip
LkCk mc song song vi ti Rt. tn s cng hng ni tip ca mch LkCk tr khng
ca n rt nh nn n ngn mch cc sng hi c tn s bng hay gn bng tn s
cng hng. Ngoi ra cun L cn c tc dng lc thm.
IV. N NH IN P
Nhim v n nh in p (gi tt l n p) mt chiu ra ti khi in p v tn
s in li thay i, khi ti bin i (nht l i vi bn dn) rt thng gp trong
thc t. in tr ra ca b ngun cung cp yu cu nh, hn ch s ghp k sinh
gia cc tng, gia cc thit b cng chung ngun chnh lu.
Vic n nh in p xoay chiu c nhiu hn ch nht l khi in p li
thay i nhiu. Dng b n p mt chiu bng phng php in t c s dng
ph bin hn c bit khi cng sut ra ti yu cu khng ln v ti tiu th trc tip
in p mt chiu.
Cc dng b n p trn thc t c chia lm ba loi chnh: n p kiu tham s (np dng it Zener), n p kiu b tuyn tnh (mch n p c hi tip) v n p xung.
Trong phm vi ca n ny chng ta ch xt n mch n p c hi tip vinguyn tc thc hin cc s n p c hi tip, phn loi v mt s loi IC n p
tuyn tnh.
1. Nguyn tc mch n p c hi tip
nng cao cht lng n nh, ngi ta dng b n p kiu b tuyn tnh (cn gil n p so snh hoc n p c hi tip). Nguyn tc lm vic ca cc s n nhc hi tip c biu din nh sau
Hnh 1.11: S khi minh ha nguyn tc lm vic ca cc
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A
PHN TIU KHIN
B KHUCHI
B SO SNHNGUNCHUN
(in p mt chiucha n nh)
nh)
UrUr
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mch n nh c hi tip
Trong mch ny, mt phn in p (dng in) ra c a v so snh vi
mt gi tr chun. Kt qu so snh c khuch i ln v a n phn t iu
khin. Phn t iu khin thay i tham s lm cho in p (dng in) ra trn n
thay i theo xu hng tim cn n gi tr chun.
Hnh sau minh ha phng php ly tn hiu a v mch so snh khi n p
v n dng.
Hnh 1.12: Cch ly tn hiu a v b so snh
a. Khi n p b. Khi n dng.
C th thy rng, tt c cc ngun p (Ri ) c
thc hin theo phng php hi tip, u l nhng mch n p hoc n dng. Tuy
nhin do yu cu v mt cng sut nn, nn trong cc s n p hoc n dng cn
c thm mt b khuch i cng sut mc trong mch hi tip.
Ty theo phng php cu trc, cc s n nh c hi tip c chia thnh
hai loi c bn: n nh song song v n nh ni tip.
S khi b n p kiu song song c cho hnh 1.13.a, nguyn l lm
vic ca loi s ny nh sau: Phn t iu chnh D iu tit dng in trong gii
hn cn thit qua iu chnh gim p trn in tr Rd theo xu hng b li: U2 =
U1 - URd , do in p ra ti c gi khng i. B to in p chun a E ch voso snh vi in p ra U2 b so snh v sai lch gia chng c khuch i
nh khi khuch i Y. in p ra ca Y s khng ch phn t iu chnh D. S bin
i dng in t 0 Itmax s gy nn s bin i tng ng dng in qua phn t
iu chnh t Itmax 0.
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A
Rt
Ur
R
Rtin p
a v bso snh
in pa v bso snh
a. b.
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Hnh 1.13: a. S khi b n p mc song song
b. S khi b n p mc ni tip
Hnh 1.13.b biu th s khi b n p b mc ni tip, trong phn t
iu chnh D c mc ni tip vi ti, do dng in chy qua ti cng gn bng
dng in chy qua D. Nguyn l hat ng ca b n p da trn s bin i in
tr trong ca phn t iu chnh D theo mc sai lch ca in p ra (sau khi
c so snh v khuch i). V d do nguyn nhn no lm cho U2 bin i, qua
mch so snh v khuch i Y tn hiu sai lch s tc ng vo phn t iu chnh D
lm cho in tr ca n bin i theo chiu hng l Uc trn hai cc ca D b li s
bin i ca U1. Khi ta c U2 = U1 - Uc do c s bin i cng chiu gia U1 vUc , U2 s n nh hn.
Trong hai s trn, phn t iu chnh gy ra tn hao ch yu v nng
lng trong b n p v lm cho hiu sut ca b n p khng vt qu c 60%.
Trong s mc song song, cng sut tn hao ch yu xc nh bng cng
sut tn hao trn Rd v trn phn t iu chnh D l:
( ) ( ) DDtth IUIIUUP 221 ++=
( ) Dtt IUIUU 12 +=
Trong s mc ni tip, cng sut tn hao chi do phn t iu chnh quyt
nh:
( ) ttth IUUP 2=
Vy s ni tip c tn hao t hn s song song mt lng l U tId nn
hiu sut cao hn v n c dng ph bin hn.
u im ca s song song l khng gy nguy him khi qu ti v n ngn
mch u ra. S ni tip yu cu phi c thit b bo v v khi qu ti, dng qua
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A
D
Y
Ech
U1 RtU2
Udc
D Y
Ech
U1 Rt
It
U2
Id
a. b.
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phn t iu chnh v qua b chnh lu s qu ln gy nn hng phn t iu chnh
hoc bin p.
2. B n p tuyn tnh IC
thu nh kch thc cng nh chun ha cc cc tham s ca cc b n pmt chiu kiu b tuyn tnh ngi ta ch to chng di dng vi mch, nh vic
s dng cng d dng hn. Cc b IC n p trn thc t cng bao gm cc phn t
chnh l b to in p chun, b khuch i tn hiu sai lch, transistor iu chnh,
b hn dng.
Cc IC n p thng m bo dng ra khong t 100mA n 1,5A in p ti
50V, cng sut tiu tn khong 500 - 800 mW. Hin nay ngi ta cng ch to cc
IC n p cho dng ti 10A. Cc loi IC n p in hnh thng dng l : serial 78xx
hay 79xx, LM 105, LM 309, A 723, LM323, LM 317, LM 337
Ty thuc vo tham s k thut nh in p ra, dng ra, h s n nh in
p, kh nng iu chnh in p ra, di nhit lm vic, ngun cung cp, n nh
theo thi gian.v.v. m ngi ta ch to ra nhiu loi khc nhau.
PHN II
THIT K NGUN MT CHIU N P C IN P RA THAY I T
0 -15V
I. S KHI CA KHI NGUN
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 13
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Hnh 2.1: S khi ca mt b ngun hon chnh
Cc tiu chun k thut ca khi ngun:
- in p vo 220VAV - 50Hz.
- in p ra 0 - 15VDC.
- Dng in ra ti 3A.
- Cng sut cc i 45W.II. LA CHN PHNG P THIT K
Da vo cc tiu chun k thut ca khi ngun nh trn ta la chn phng
p thit k cho tng khi ca b ngun v t a ra s nguyn l ca b
ngun:
1. Bin p
y do ngun n p c s dng li in xoay chiu (220V - 50Hz) v
cng sut cc i ca ngun l 45W (15VDC - 3A) nn ta s dng mt bin p c in
p vo 220V v in p ra 15V, dng ra 3A.
2. Mch chnh lu
Do nhng u im ca mch chnh lu cu nh in p ra t nhp nhy, in
p ngc m it phi chu nh hn so vi phng php cn bng nn ta s chn b
chnh lu cu.3. B lc ngun
B lc c nhim v san bng in p mt chiu dp mch UT thu c sau
khi chnh lu thnh in p mt chiu UO1 t nhp nh hn.
Vi nhng c im ca phng php lc bng t in nh tnh n gin
cng nh cht lng lc kh cao nn y ta s s dng phng php lc ny cho
khi ngun.4. Khi n p
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A
Bin pMch chnh
l-u B lc
n p mtchiu
(n dng)
U1~ U
2~ U
TU
O1U
O2
IT
RT
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Theo yu cu thit k mch n p c in p ra thay i t 0V n 15V nn
ta s dng mt IC n p thng dng l LM317. Do LM317 ch cho in p ra trong
di 1.2V - 35V (vi cch mc thng thng) nn ta phi s dng mt cch mc phi
hp nhm iu chnh in p ra v mc 0V bng cch dng mt khi mch to ra
in p m.
a. Nguyn l khi mch n p c in p thay i
Tng qut v IC LM317
LM 317 l mt IC n p thng
dng c ng dng nhiu trong thc t
vi cc u im nh in p ra n nh
cng nh cch iu chnh in p ra khn gin (ch cn thay i gi tr mt
phn p).
Mt s c im thng s k thut
c bn ca LM 317 nh sau:
1,2V UOUT 35V.
IOUT MAX = 1,5A.
3V UIN - UOUT 40V.
IADJ = (50 100) A.
10 mA IOUT IMAX
S nguyn l cu to ca
LM317 c trnh by nh sau:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 15
Hnh 2.2: IC n p LM317
-
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Trng Vn QuytMSSV: 0851010060 n 1
Hnh 2.3: S nguyn l IC LM317
Mch s dng IC LM317, vi cch mc thng thng (nh hnh 2.4) in p
ra ch nm trong khong 1,2V n 35V.
3
1
2
ADJ
OUTIN
LM317
0,1uF
C1 R1
R2
+
10uFC2
Hnh 2.4: S n p dng LM317
in p ra c th iu chnh c nh thay i phn p R1 , R2 . Dng in ra
ti chn ADJ c gi tr rt nh (50 - 100A). in p trn R1 l 1,25V. Khi inp ra c tnh theo cng thc:
21
2125,1 RIR
RU ADJra +
+=
Do IADJ c gi tr rt nh nn c th tnh gn ng Ura nh sau:
+=
1
2125,1R
RUra
Phng php iu chnh Ur v mc in p 0V:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 16
-
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Trng Vn QuytMSSV: 0851010060 n 1
c th iu chnh Ur v mc 0V ta s dng cch mc mch phi hp nh
sau:
3
1
2
ADJ
OUTIN
LM317
0,1uF
C1 R1
R2
U1
Hnh 2.4: S nguyn l chnh mc in p ra v mc 0V.
Nguyn l chnh Ur v mc 0V nh sau:
T s nguyn l ta c:
+=
1
2125,11 R
RUrU
11
2125,1 UR
R
rU +
+=
Nu ta c gi tr U1 -1,25V th khi ta c th iu chnh c in p U r
v mc 0V.
b. Nguyn l ca khi to in p m
Ngun m c th c to ra n gin bng cch s dng mt cun bin p
c u ra m v dng. Nhng y ta s to ra mt ngun m bng cch dng cc
ngun dng c sn.
Vic to ra in p m t cc ngun in p dng c sn da trn nguyn l
ca mt ngun xung c bn s dng s phng v np ca cc t in theo chu k
nh tc dng ca mt xung vung c to ra t mt khi mch to xung.
S khi mch nh sau:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 17
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Trng Vn QuytMSSV: 0851010060 n 1
LM7812
1
2
3
GND
+12VIN
+
C6 C7
8
37
2
6 5
4
1
VCC
OUT
GND
DISC
RST
CNTLTHR
TRIG
LM555
R1
R2
+
C1
C2
+
1000uF
C3
+1000uF
C4
1N4007D1
1N4007
D2
2
1
3
GND-5VIN
LM7905
12V
C5
DC IN
DC OUT (-5V)
Hnh 2.5: S nguyn l ca mch to in p m
Trong : Cc IC LM7812, LM555, v R1 , R2 , C1 , C2 c tc dng to ra mt
xung vung c tn s c xc nh theo R1 , R2 , C1 v bin khong 7,4V (theo
c tnh ca IC555). Khi to xung xung ny c th c thay bng bt k mt
mch to xung vung khc (v d nh mch a hi dao ng, mch dao ng dng
mch di pha ...)
Khi ti chn s 3 (chn OUT) ca IC 555 s c mt xung vung c bin
l U0 = 7,4V. Khi xung vung mc cao, dng in t chn 3 np vo t C3 ri qua
D1 xung t do t C3 c tch in.
Khi chn s 3 mc thp 0V, khi c th xem cc (+) ca t C 3 c nixung t. Trc t C3 c tch in U0 - 0,7 = 6,7V, do lc ny ti cc (-)
ca t C3 s c in p l - (U0 - 0,7) = - 6,7V, in p m ny s ko dng qua diode
D2 lm cho ti catot ca s tn ti mt in p m c gi tr - (U0 - 0,7) + 0,7 = 6V
nh c LM7905 in p ny c gi n nh mc -5V. Cc t C 4, C5 ng vai tr
l cc t lc.
Vy u ra ca mch ta to ra c mt in p m c gi tr - 5V.
c. Cch tng dng in ra ti
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 18
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Trng Vn QuytMSSV: 0851010060 n 1
Do IC LM317 ch c th cho dng in ra ti cc i l 1,5A do c th
t c dng ra ti l 3A ta c th mc thm transistor iu chnh phi hp vi IC
n p nh sau:
3
1
2
ADJ
OUTIN
LM317U1
104
C1R1
R2
T
R3
DC OUT
-5V
U1
DC IN +C2
Hnh 2.5: IC n p dng thm transistor ngoi tng dng s dng.
T s ta c Ir = IC IE . Khi transistor tr thnh phn t chu dng thay
cho IC n p. Do vy ch cn chn loi transistor c kh nng chu c dng in
mong mun (3A) v tnh ton phn cc cho transistor hot ng.
PHN III:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 19
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Trng Vn QuytMSSV: 0851010060 n 1
TNH TON CC THNG S K THUT V LP RP MCH
THC T
I. TNH TON CC THNG S CHO TNG KHI MCH
1. Bin p
Hnh 3.1: Bin p ngun
Vi ch tiu Ura max = 15 V, theo c tnh k thut ca LM317 th in p vo
IC cn tho mn 3V UIn - UOut 40V, do UIn = 18V, mt khc phi cng thm
mt lng in p ri trn hai diode chnh lu, do in p ra trn cun th cp l
U2 = UIn + 2 0,7 = 19,4 V.
Xt khi in p li c gi tr nh nht U li min = 200 V, v vi in p ra yucu trn cun th cp l 19,4V ta c:
154,19
22002
22
1
2
1 ===U
U
U
U
n
n luoi
Khi in p li c gi tr ln nht Uli max = 240 V, in p ra ln nht trn
cun th cp:
2315
12240
1
212 ===
n
nUU (V)
Ta c dng in ra trn khi ngun cng l dng in ra trn cun th cp ca
bin p: Ira = I2 = 3A.
Do cng sut ln nht m bin p cung cp l:
P2 = U2 Ir= 23 3 = 69 W
Gi s rng tn hao trn hai diode chnh lu l 10% th cng sut thc ca
bin p l: 77%90
692 ==P W
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 20
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Trng Vn QuytMSSV: 0851010060 n 1
Dng in chy trn cun s cp l: 2,015
3
152
1 ===I
I A
tnh din tch thit din ca li bin p ta da vo cng thc:
( ) PS 3,18,0 = (cm2)
( ) 93,18,0 77 =S (cm2)
Do ta la chn din tch tit din ca li bin th l 9 cm 2, v dng thp k
thut Tn - Silc.
Tnh ng knh dy cun bin p theo ch tiu mt dng 3A/mm
- Cun s cp: I1 = 0,2 A
07,0
/3
2,0
/322
11 ===
mmAmmA
IS (mm2)
ng knh dy cun bin p trn cun s cp:
3,007,0
22 11 ===
Sd (mm)
- Cun th cp: I2 = 3A
1/3
3
/3 222
2 === mmAmmAI
S (mm2)
ng knh dy cun bin p trn cun th cp:
128,11
22 22 ===
Sd (mm)
Tnh s vng dy ca bin p:
Da vo t s:( )
( ) ( )245
cmSUVol
nVong= ( )211
45
cmSUn =
Xt khi Uli max = 240 V th s vng dy trn cun s cp l:
( )1200
9
45240
45211
===cmS
Un (vng)
S vng dy trn cun th cp l:
8015
1200
151
2 ===n
n (vng)
Vy ta la chn bin p c cc c tnh sau:
- Din tch tit din li bin p: S = 9 cm2
- ng knh dy cun bin p:
+ S cp : d1 = 0,3 mm + Th cp: d2 = 1,128 mm
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 21
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Trng Vn QuytMSSV: 0851010060 n 1
- S vng dy cun bin p:
+ S cp : n1 = 1200 vng + Th cp: n2 = 80 vng
2. Khi chnh lu
Khi in p li c gi tr ln nht U li max = 240 V, in p ngc t lndiode chnh lu:
2315
122402
1
212 ====
n
nUUUng (V)
Dng in ln nht qua diode: ID = I2 = 3A.
H s gn sng (khi Ct = 0) W = 0,49.
Tn s ca in p ra b chnh lu: 100Hz
Do ta la chn diode chnh lu loi: IN5408.
3. Khi lc ngun
Sau khi qua khi chnh lu cu th t lc cng phi m bo chu c
in p ln nht l 23 V. Do ta chn mt t lc c Umax = 25 V.
xc nh in dung ca t ta da vo gn sng sau khi chnh lu:
gst
CLL
KR
TC
3
=
Chn gn sng sau khi chnh lu l Kgs = 5% = 0,05.
Chu k chnh lu: 01.050.2
11===
CL
CLf
T (s)
in tr ti tng ng: 53
15===
r
rt
I
UR
Khi : 013,005,0.5.3
01,0
3===
gst
CL
L KR
T
C (F)
Vy ta chn t lc : 2200 F / 25V.
3. Khi phn p ly in p ra
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 22
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Trng Vn QuytMSSV: 0851010060 n 1
3
1
2
ADJ
OUTIN
LM317U1
104
C1
680
R1
10K
R2
-5V
DC OUT (0V : +15V)
U1
DC IN
Hnh 3.2: Khi phn p
Phn p R1 v R2 c nhim v lm thay i in p ra theo s bin thin ca
bin tr R2.
T s ta c:
+=
1
21 125,1 R
RUUr
11
2125,1 URRUr +
+=
Khi to in p m c nhim v to ra mt in p m U 1 = - 5V. Khi
to ra mt in p bin thin t 0 - 15 V th:
15125,10 11
2 +
+ U
R
R
20125,151
2
+
R
R
1531
2 R
R
121 153 RRR
Nu chn R1 = 560 th ta c 1,68 K R2 8,4 K. Nh vy ta c th
chn mt bin tr 10K.
4. Khi to in p m
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 23
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Trng Vn QuytMSSV: 0851010060 n 1
Khi to in p m c xy dng trn c s mt ngun xung c bn cho
in p ra l - 5V (do s dng IC n p LM 7905) v dng ra ti c th t n 1A
(theo c tnh ca IC LM555 v LM7905).
LM7812
1
2
3
GND
+12VIN
U2
+
100uF
C5
104
C6
8
37
2
6 5
4
1
VCC
OUT
GND
DISC
RST
CNTLTHR
TRIG
LM555
U3
1K
R4
10K
R5
+
1uF
C7
103
C8
+
1000uF
C9
+1000uF
C10
1N4007D6
1N4007
D7
2
1
3
GND
-5VIN
LM7905U4
12V
-5V
104
C11
DC IN
DC OUT (-5V)
Hnh 3.3: Khi to in p m.
Ngun cung cp: Ta s dng mt ngun n p n gin vi IC LM7812
to ra mt in p n nh +12V, cung cp cho IC to xung.
Khi to xung vung: IC LM555 c nhim v to ra mt xung vung c
tn s v bin n nh.
Tn s do LM555 to ra c tnh theo cng thc:
( )BA
RRTf
2
44,11
+==
Nu chn RA = R4 = 1K, RB = R5 = 10K v C = 1 F th tn s ng m ca t
C9 l:
( ) ( )131
10.1010
44,1
2
44,11643=
+=
+==
BA RRTf (Hz)
Nguyn l hot ng ca mch c gii thch nh phn II v in p ra
lun t -5V n nh do s dng LM7905.
5. Transistor tng dng ra ti
tng dng ra cho ngun ta s dng cch mc nh sau:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 24
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Trng Vn QuytMSSV: 0851010060 n 1
3
1
2
ADJ
OUTIN
LM317U1
104
C2
680
R1
10K
R2
B688T
2.2/0.5W
R3
DC OUT (0V : +15V)
-5V
U1
DC IN
Hnh 3.4: IC n p dng thm transistor ngoi tng dng s dng.
Do dng ra l 3A ta phi s dng mt transistor c kh nng chu c dng
ln hn hoc bng 3A. y ta s s dng transistor B688.
T s trn ta thy phn cc cho transtor hot ng th st p trn in
tr R3 phi l 0,7 V, dng qua n l 0,3A (Dng qua LM317). Do ta chn in tr
R3 nh sau:
( )=== 2.23,07,0
1
1
3R
R
IUR
( )WIUP RRR 21,03,0.7,0. 111 ===
y ta s dng mt in tr c R3 = 2,2 , cng sut P = 0,5 W.
6. Khi lc in p ra
tng n nh cng nh lc cc nhiu ca in p ra ta s dng thm
mt khi lc in p ra gm t C3 = 100F / 25V v C4 = 100 nF.
Sau khi tnh ton chi tit cho cc khi ta tin hnh ghp ni cc khi vi
nhau thnh s nguyn l nh sau:
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 25
-
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Trng Vn QuytMSSV: 0851010060 n 1
S Layout
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 26
+
1 0 0 u FC 1
L M 7 8 1 2
1
2
3
G N D
+ 1 2 VI N
U 2
+
1 0 0 u F
C 5
1 0 4
C 6
8
37
2
6 5
4
1
V C C
O U T
G N D
D I S C
R S T
C N T LT H R
T R I G
L M 5 5 5
U 3
1 K
R 4
1 0 K
R 5
+
1 u F
C 7
1 0 3
C 8
+
1 0 0 0 u F
C 9
+1 0 0 0 u F
C 1 0
1 N 4 0 0 7
D 6
1 N 4 0 0 7
D 7
2
1
3
G N D
- 5 VI N
L M 7 9 0 5U 4
6 8
R
L
3
1
2
A D J
O U TI N
L M 3 1 7U 1
1 0 4
C 21 0 4
C 4
5 6 0
R 1
1 0 K
R 2
1 2 V
- 5 V
ACIN22
0V)
D C O U T :
+
1 0 0 u F
C 3
1 0 4
C 1 1
D 1
D 2
D 3
D 4
B 6 8 8T
2 , 2 / 0 , 5 W
R 3
B i e n a p
snguynlngunmtchiu
np
cinp
r
athayi(0
15V)
3A
-
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Trng Vn QuytMSSV: 0851010060 n 1
S mch thc t
KT LUN
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 27
-
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Trng Vn QuytMSSV: 0851010060 n 1
Sau mt thi gian tm hiu v thit k, em hon thnh n thit k ca
mnh vi yu cu thit k khi ngun mt chiu n p c in p ra thay i (0
15V) 3A. Kt qu thit k c lp rp thnh mch in v kt qu hot ng ca
mch t c nhng yu cu thit k.
Qua ti thit k ny gip em c th p dng nhng kin thc hc vo
thc t ng thi nng cao kh nng t tm hiu v thit k cc mch in tng t.
T nhng kin thc thu c trong qu trnh thc hin n ny s gip em c
thm kinh nghim thit k cc mch in mi c phc tp hn.
Cui cng em xin chn thnh cm n thy gio: Th.s V nh Tng tn
tnh hng dn gip em hon thnh n thit k ny.
Sinh vin thc hin
Trng Vn Quyt
Ti Liu Tham Kho
Thit k mch ngun DC n p c in p ra thay i 0-15v, 3A 28
-
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Trng Vn QuytMSSV: 0851010060 n 1
DATASHEET ca cc IC LM317, LM 7812, LM 555, LM 7905, vTransistor B688
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