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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 ,