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Li MuNgy nay vi stin bca khoa hc cng ngh, cc thit bin tngy cng c ng dng
rng ri trong hu ht cc lnh vc Kinh t-X hi, cng nh trong i sng hng ngy. Trong tt cthit
bin tni chung th vn ngun lun l vn cn phi quan tm v xem xt cn thn, v n quyt
nh n tnh an ton ,n nh v vn hnh hiu quca hthng. Hu hit cc thit bu sdng
ngun 1 chiu cn p cn thn. Khi tnh ton thit kngunn p cho mt mch in tth ta c
hai hng thit k: mt l thit kngun tuyn tnh , hai l thit kngun xung. th vi trnh pht
trin ca kthut hin i th ngun xung cng tr c u thvt tri so vi ngun tuyn tnh v
hiu nng, cng sut, tnh nhgn, . C rt nhiu m hnh ngun xung cho ta la chn : m hnh
ngun xung kiu Buck , m hnh ngun xung kiu Boost , hay m hnh ngun flyback, ti ny emchn ngun flyback tm hiu, v tnh linh hot ca n, c thto c nhiu u ra theo mun, c
ththit ku ra tng p hay gim p ty theo thit kmong mun.
Em xin cm n thy gio TS. Nguyn Hng Quang hng dn gip em hon thnh n ny,
do kin thc bn thn cn hn ch, nn c nhiu thit xt, mong nhn c sgp ca thy v cc
bn.Em xin chn thnh cm n.
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MC LC
I.L THUYT V TNH TON MCH
1.
L thuyt v mch ngun Flyback.............................
1.1.ChLin Tc.
1.2.ChGin oan
2. Thit k Mch Flyback...
2.1. Nhim VThit K.
2.2. Tnh Ton Phn Mch Lc
2.3. Tnh Ton Phn Mch iu Khin..
3. M phng....
II.KT QU T C V PHN TCH LI t chi tit cc vn gp phi, cch gii uyt, c th bao gm mi hnh nh
minh ha
III.KIN NGH D N C TH M RNG
a ra cc kin ng gp cho n c th c m rng trong tng lai, gipsinh vin c th hon thin hn thit k ny....................
IV.KT QU.
V.TI LIU THAM KHO.
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I. L THUYT V TNH TONMCH1. L thuyt vmch ngun Flyback.
M hnh ngun flyback thng dng c dng nh hnh i.
Hnh 1: M hnh Flyback
Tuy nhin khi phn tch ta gisbin p l bin p l tng v nng lng ttrngtrong n
c m tbng cun cm Lm nh hnh vi :
Hnh 2: M hnh bin p xung
Nguyn l hot ng ca mch flyback c m tnh hnh i :
Nh hnh vta thy n gm : 1 MOSFET cng sut hot ng nh mt kha ng ct,1 ioe
cng sut, mt tlc ng ra C, mt bin p xung, c nhim vcch ly u vo v u ra, v tch ly nnglng ttrng. Mch ngun flyback thng dng cho cc bngun c cng sut t20W n 200W.
n c hai chhot ng : CCM (dng lin tc) v DC (ong gin on). sau u ta sphn tch qua
tng chmt.
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Hnh 3: Nguyn l hot ng
1.1. Chdng in lin tc (CCM).
a. xt trong khong thi gian 0
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V gi trng in p mch : ( ) (0)m m m
iL L L
m
V DTi i DT i
L
Hnh 4:
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Gishiu xut l : 100% , t ta c mi quan hgia in p u vo v in p u ra l :
0
(1 )Vdc
i
V DM
V n D
-in p hai u diode l : 00( )
id
V VV Vn D
in p cc i trn diode 0
min
dVV
D .
- ng in nh chy qua MOSFET l : 0 02 (1 ) 2
m mL L
SM i
i ii ii i
n n D
ng in nh cc i chy qua MOSFET l : ax0 0 axax
ax2 (1 ) 2
m mmL LmSMm i
m
i ii ii i
n n D
b. xt trong khong thi gian TD < t < T.
Trong khong thi gian ny MOSFET kha, diode dn (hnh v3_b).
-khi in p hai u diode bng 0, dng chy qua chuyn mch MOSFET bng 0; 2 0V V
-in p hai u cun cm Lm l :0
LmLm i m
diV V nV L
dt
dng chy qua cun cm Lm l : 0 ( ) (0)iLm Lm
nV V DT i t DT i
Lm Lm
-ta c : dng chy qua cun s cp bin p l : 1 Lmi i = 0 ( ) (0)i
Lm
nV V DT t DT iLm Lm
dng chy qua diode thcp l : 2 1di i ni 2
0 ( ) (0)iLm
n V nV DT t DT ni
Lm Lm
Ta c : 00SM i
nVV V nV
D in p cc i t ln MOSFET : 0axSMm
min
nVV
D .
-ng in nh chy qua diode l : 01 0
2 1 2
Lm Lmdm
n i i n ii ni i
D
ng in nh cc i chy qua diode l : 0 axax
1 ax 2
Lmmdmm
i n ii
Dm
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Cn ch rng trong chlin tc ny, gia in p vo v in p ra c mt mi quan h:
(1 )vdc
DM
n D
c. Bin gii gia hai chCCM v DCM.
Hnh 5: M tmch Flyback bin gii gia chCCM v DCM
Hnh vtrn m tdng sng ng in bin gii gia hai chCCM v DCM. T ta
ng tnh c ng in qua cun cm Lm:
( ) iLm
m
Vi t t
L vi : 0 t DT
0(1 )
(0) iLm Lmm m
V DT nV D T i i
L L
0 minax(1 )
Lmm
m
nV D T i
L
.
-td ta c dng 1 chiu chy qua cun cm ranh gii gia 2 chDCM v CCM l :
max
2
Lm xLmB
ii
nng lng tch trtrong cun cm chny l :
2
maxW2
Lm mOB
i L cng sut u ra :
2 2
0 minW (1 )
2
OBOB
m m
n V DP
T f L
-
Mt khc ta c :2
0OB
L
VP
R
2 2
min minmin
(1 )
2
Lm
m
n R DL
f
.
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1.2. Chdng gin on.
a. Xt trong khong thi gian 0
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Hnh 5: dng sng ng in v in p mch ngun flyback chgin on (DCM)
b. Xt trong khong DT < t < (D+D1)T .
Trong khong thi gian ny Mosfet kha cn Diode m, khi ng chy chuyn mch Mosfet bng 0,
v in p 2 u diode bng 0. Khi 2 0v V
in p 2 u cun cm v cun s cp MBA l: 1 2 0Lm
Lm m
div v nv nV L
dt
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t ng chy qua cun cm l:0 1( )
Lm
m m
nV V DTi t DT
L L
ng nh cc i chy qua cun cm l:0 1
Lm
s m
nV Di
f L
ng in chy qua cun s cp MBA l:0 1
1 ( )
Lm
s
nV nV Di i t DT
Lm f Lm
ng in chy qua cun thcp MBA l:
2
0 12 1 ( )D
s
n V nV Di i ni t DT
Lm f Lm
ng nh cc i chy qua diode l:1
DM SM
s
nV Di nI
f Lm
do: 1 2 0v nv nV ,
in p nh cc i chy qua Mosfet l: 1 1 1 0s SMv V V v V nV
vi: ax 1 ax 0SMm mV V nV
c. khong thi gian : 1( )D D T t T
.
Trong khong thi gian ny cDioe v osfet u kha. Khi ng in chy qua cun thcp va
Diode l: 2 0Di i V ng in chy qua Mosfet v cun s cp l: 1 0Si i
Khi ng ua cun cm l 0Lmi
. suy ra v1 = 0 = v2 , din p qua Mosfet l 1sv V
, V
in p 2 u ioe l 0Dv V
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2.
Thit KMch Flyback.
2.1. Nhim VV yu Cu Thit K.
-
Flyback l mt dng ca mch ngun xung c dng phbin nht hin nay, vi u im l
hiu xut chuyn i rt cao (t75-85%, thm ch cn hn ), ngoi ra n cn cho php thit kvi nhiu
u ra khc nhau v c cc tnh khc nhau.
-
Yu cu thit k: bi ny em sthit kmch flyback vi di in p u vo l 15-32V (ngun
ly tsc laptop), v yu cu ln nh p u ra 5V, v dng ti a cung cp l 1A.
- tyu cu bi ton, chlm vic ca m hnh flyback sc la chn trong ti ny l
chkhng lin tc v :
+gim c kch thc ca bin p xung.
+Lm nh, o gim c in p ngc tc ng ln MOSFET, khng phi chto
mch kha ioe, o n gin trong cng vic thit khn.
+ ng nhanh vi thay i u ra.
+ tuy nhin nhc im ca chkhng lin tc l gai in p u ra ln, tuy nhin do
ti mang tnh cht tm hiu, o c thchp nhn v khc phc c bng tlc u ra.
2.2. Tnh Ton Phn mch Lc.
S nguyn l mch DC-DC Flyback Converter nh hnh i.
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Nh trn s ta thy, phn mch c chia thnh 2 phn l phn lc v phn iu khin. sau y ra s
i tnh ton chi tit tng thnh phn cho mch flyback.
a. tnh ton v chn MOSFET v diode.
Ta gi 0vdci
VM
V l hm thhin mi quan hgia p u ra v p u vo.
theo nh yu cu bi ton : 15 32iV V v u ra Vo 15V, o chnh mc, ta c thtnh
c vdcM max v min nh sau:
ax
min
5
15
ovdcm
i
VM
V
min
max
5
32
ovdc
i
VM
V
Nh phn tch trn th ta thy, chkhng lin tc th nn c mt khong thi gian c
OSFET v DIODE u kha, v theo nh kinh nghim th khong thi gian ny thng ly l 0.2T. gi
sDmax = 0.4, khi ta c thtnh ton tsvng dy cun s cp v thcp theo cng thc sau:
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ax min
ax
( 1)
0.8( 1) ( 1)
m in
o m o
D Vn
V D V
= 2.33 chn n=2.5 (ch l n l tssvng dy cun s cp v th
cp ca bin p xung).
Chn tn sng ct : f = 10Khz. T ta c thtnh gi trmax ca Lm mch hot ng
chDC nh sau:
2 2
min ax
ax2
in mm
om
V DL
P f
= 306 uH. chn Lm = 300uH.
T ta c thtnh ton li gi trDmax v Dmin nh sau:
min min
min
2m
vdc
L
fLD M
R = 0.1875
max ax
min
2 mvdcm
L
fLD M
R = 0.3961
Dng nh cc i chy qua MOSFET v Diode c thtnh ton c theo cng thc sau:
min maxmax
iSM
m
D VI
fL = 1.9808 A
max maxDM SMI nI = 4.95 A
V in p ngc cc i t ln MOSFET v Diode c thtnh c nh sau :
max maxSM i oV V nV = 45 V
maxmax
iDM o
VV V
n = 18 V
Do vy ta c thchn MOSFET l IRFZ530N v diode l diode shottky U860 (chn diode xung cho php I
ln hn 5A ).
Tnh ton tlc u ra: gismong mun in p p mch u ra rippleV 300mV. Khi ta tnh
c gi trca tC cn thit theo cng thc sau: max axo moripple
I DC
V f = 622.67uF, tht ra tC chn cng
ln cng tt, ngoi thtrng c t1000uF/50V. o tC chn c gi tr1000uF/50V.
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b. Tnh ton mch bo vsnubber cho MOSFET .
nh ta bit th khi OSFET ng t ngt th dng qua n gim rt nhanh, v trong mch c
cun cm , o m in p ngc t ln MOSFET srt ln v c thlm hng OSFET, o ta cn
phi c mch bo vmosfet:
Gista gi Vmt l in p cc i mong mun t ln mosfet. Do ta cn phi c
maxMpeak mt SMV V V ( tra trong datasheet ca IRFZ530N th ta c MpeakV = 100)
Chn mtV = 80V.
C mt i lng ta cn quan tm ti khi ng ct mosfet l in cm gi ca bin p, ta gi l : Lk.
Thng thng Lk thng ly l 0.3Lm (nu thit kbin p xung tt th Lk = 0.1Lm hoc nhhn na).
0.3k mL L = 3uH.
cng sut max tiu tn trn in trRs ca mch snubber l :2
0.5s kP L I f = 0.161 w .
in p ri trn in trRs (mch snubber) l Vs = Vt-Vin = 48V -- >2
ss
s
VR
P = 5.6 kohm
chon in trRs l 15k/0.25W
Tin mch snubber c xc nh nhvo cng thc sau : sss
TC
R = 17857,14 pF
chn tin l 20pF, tng ng l 3 con 104 ghp song song vi nhau.
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Bin trRV1 trong mch c nhim vto phn p phn hi in p vkhi mch iu khin,
lng ph cng sut trn RV1 th ta chon RV1 l bin tr50K.
c. Tnh ton bin p xung.
chn c kiu li ferit sdung th ta dung cng thc sau ng chng kiu loi:
w.
. . .
o cmap e
P DA A A
f B k
w,
eA A tng ng l din tch vng li qun, v din tch cung cp ta qun dy. Hai
thng sny cho catalog ca li ferit.
Po l cng sut u ra.
Dcma ly 250 mA
F la tn sng ct.
B l cm ng in tbo ha . ly l 150 Guass
K l hsphthuc mch : i vi flyback ly l 0.00025 ; v l hiu xut ca mch.
(ngoi ra chn li ferit th ta c thda vo cng sut ng ra yu cu m linh hot chn la cho ph
hp).
Hin ti mnh c li EE25, tnh ton ra th n p ng kh tt chtiu ca cng thc trn.
tnh svng dy th ta da vo cng thc sau :
.
p pk
p
e
L IN
B A
= 42.56 --> chn svng cun s cp l 43 vng. -->svng cun
thcp l 18 vng.
tnh kch thc li dy th ta phi tnh ng in hiu dng chy qua bin p.
ax
3
mrms pk
DI I = 0.7198 A
Gismong mun mt ng in l 5A/mm2 -- >ng knh li dy qun cun s cp l 40mm.
Tnh ton tng tta tnh chn ng kch li thcp l 40mm, nhng l 2 si dy.
2.3. tnh ton phn mch iu khin.
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a. tm hiu vIC TL494.
Hnh dng ca chip TL494 :
S khi ca IC Tl494 c m tnh hnh i :
Chc nng ca cc chn c m tnh sau (so snh vi s khi dhiu):
-Pin 5 v Pin 6 : y l 2 chy to ao ng xung rang ca, bng cch mc thm in trv t
to ra xung rang ca c tn s:1
fRC
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Ta c thc tnh sau chn R v C
-PIN 4 : chn thit lp chkhi ng mm , n gip mchn nh khi khi ng
-Pin 1 v Pin 2: y tng ng l u vo ng v m ca mch so snh m ta ung phn
hi u ra viu khin.
- Pin15 v Pin 16 : hai chn ny c chc nng tng t Pin 1 v Pin 2, n nhm mc nh gii
hn dng cho mch ngun. tuy nhin trong ti ny n gin th ta tm ko dung chc nng ny, o
haichn ny sc ni tng ng vi hai chn 1 v 2.
- Pin3 : chn phn hi, nh ta bit th mch OPAM c hskhuch i rt ln, n c thlm
mtn nh mch ngun, o k c mch ngun th ta cn phi iu khin c hskhuch
i ca OPAM.
- Pin 7 v Pin 12 tng ng l 2 chn ni t v cp ngun cho TL494.
-Pin 14 : y l chn to in p chun 5V.
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- Pin 8, Pin 9, Pin 11 v Pin 10: y tng ng l cc chn C v E ca transistor BJT. Ts khi
trn ta c thla chn linh hot c iu khin cn thit nh mong mun.
Thng thng th transistor NPN th cc E c ni t, v dung cc C iu khin (cc C trong
trng hp ny l trng thi cao tr.), do khi ung ta phi ng thm 1 in trko ln Vcc
b. tnh chn thng scho mch iu khin.
- tnh chn tn s: chn R = 10k , thy vo cng thc1
fRC
=10kHz -> C = 0.01uF -> chn
tgm 103.
-tnh chn mch phn hi : tht ra mch phn hi trong bi ton chn c dng
Theo m hnh mch phn hi trn ta dng xc nh c biu thc u ra ca OPA theo Vo nh
sau : gi Kpa l hsphn p , gi in p u ra ca OPA l Vcut. Khi ta c biu thc sau:
ef effr
cut r o
pa a pa
RVV V VK R K
.
Gista c u vo Vin =32V -> D= 0.1857 .
n gin th ta chn Kpa = 2.
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Hskhuch i th ta t nh, khi chy mch th tng hskhuch i ln dn.
3. M Phng.
Kt qum phng bng PSI c minh ha hnh vi, u ra p ng kh tt khi thay
i ti.
S nguyn l mch vtrn PSIM
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p ng u ra vi ti 1A
p ng u ra vi ti 0.2A
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II. Kt Qut c V Phn Tch Li.
Sau ti ny th chng em lm uen vi cng vic thit k, v c bit l thit kmch
ngun xung. t c khnng ttm hiu v xy dng cc m hnh mch ngun xung thc tthng
dng khc na nh l : buck converter, boots converter, .
Bi thit kc kh khan ch, do chdng biu khin P n thun v hskhuch i c
tm theo phng php , mt kh nhiu thi gian v ngoi ra chn khng cn thn th mch ddn
n trng thi mtn nh.
III. Kin NghMRng Ti.
Sau khi hon thnh ti ny th ta c thc mt vi hng mrng ti nh sau:
+ Vic tm kim mt u vo DC i khi kh tn km, o ta c thngh n hng l ly trc tip t
ngun 220Vac, sau cho ua mch chnh lu c p DC, sau a vo mch flyback.
+ cho linh hot cho cc ng dng cn cc u ra khc nhau, v dcp cho ng c, cp cho vk, th
ta c thchto cho php c nhiu u ra mong mun.
+ Trong ti cha tnh n vic bo vu ng, o ta c thmrng cho bi ton chng qu
ng. V m hnh iu khin theo chphn hi ng in cng l mt bi ton ta mrng cho
mch flyback.
+ Trong bi chsdng biu khin P n thun, v hskhuch i l o ta thay i trong thc
nghim, kh mt thi gian, o rt ngn thi gian v c cht lng tt hn th ta nn m hnh
ha mch flyback trc khi xy dng biu khin.
IV. Kt Qu.
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S mch nguyn l vtrong Altium designed :
S mch in vtrong Altium designed :
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Mch thi cng.
Danh sch linh kin.
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V. Ti Liu Tham Kho.
1. Pulse-width Modulated DC-DC Power Converters -Wiley 2008.
2. Transformer design example.
3. Switch Mode Power Supply (SMPS) Topologies_MicroChip_Part1
Switch Mode Power Supply (SMPS) Topologies_MicroChip_Part2
4. web : ti.com. microchip.com. reseach key : esigne power supply flyback ,