Bi 3.5: Cho chui xung kch S1 on/off hnh 3.18 nh hnh BT3.5. V dng sng in p ti cc im: trn S1, trn cathode D3, trn cun th cp ghp ra ti(anode D1).

Khi Q1 dn, Q2 tt, dng in c truyn qua T1 v D1 dn,np cho L1 v ti, lc ny D2 tt . Khi Q2 dn, Q1 tt, dng in truyn qua T1, D2 np cho L1 v ti, D1 tt . Trong khong thi gian Q1 tt Q2 cha dn ,L1 x dng ra ti v D2, ngc li Q2 tt Q1 cha dn, L1 x dng ra ti v D1.Trong khong thi gian gia Q1 va off v Q2 chun b on th khng c kha no dn nn 1 in p ln xut hin gia cc C v E ca 2 BJT e da nh thng 2 BJT ny. Khi trong thi gian kha ny dn th s xut hin 1 in p bng 2 ln in p vo trn cc CE ca kha kia cng c th l 1 nguyn nhn gy nn nh thng BJT.C th:R1, C2, D3 lm mch kp p trn BJT Q2 trong thi gian off . Nu khng c mch kp ny, in p trn Q2 trong thi gian off rt cao c th nh thng Q2.R2, C3, D4 lm mch kp p trn BJT Q1 trong thi gian off . Nu khng c mch kp ny, in p trn Q1 trong thi gian off rt cao c th nh thng Q1.

Bi 3.7: Gii thch ti sao ngun n p xung fly back thung phi s dng bin p xung c khe h t,trong khi dng forward li khng cn khe h t.Cho bit chc nang ca khe h t.Ngun n p xung fly back thng phi s dng bin p xung c khe h t, trong khi dng forward li khng cn khe h t:Do nhc im ln nht ca mch flyback l phn ln nng lng tch tr trong bin p di dng dng DC trong cun dy( s cp lun c dng mt chiu). Do cn phi s dng li kch thc ln hoc li phi c khe h t trnh bo ha t, dn n gim cng sut my bin p.i vi mch forward c 2 dng loi c bn v loi y ko. Dng DC qua s cp lun bng khng do loi tr c nng lng tch tr trong bin p.Vy chc chnh ca khe h t l chng bo ha t. Khe h t lm gin on ng sc ghp qua mch t dn ti t tr tng lm gim cng t trng. V vy khi c dng t bin cng cha bo ha t.Bi 3.9: Thit k cun dy cho ngun buck Vin= 12+ 20%, Vout= 5V, Iout= 2ATa chn fo= 50kHz ta c

Ta tnh T hnh 3.26 1mJ dn n tm c li kch thc 23x13 v AL= 200

Aw cho cun dy c 2 ngn l 0.138 cm2 ng vi li 23x13 theo bng 3.5 v hnh 3.28

Tm T= 47.82T bng 3.6 ta chn dy #16

Bng 3.6 cng cho dy #16 c in tr 4.020/1000feet. Chiu di trung bnh 1 vng vi li 23x13 l 0.145 feet theo bng 3.5

R=NIwrw= 6,6.0,145.4,020.10-3= 0,0038 Vi dng nh Ipk= 10,643A, cng sut mt mt trung bnh

Cng sut ra Pout= Vout.Iout= 10(W)=> cng sut mt mt chim 1,45% so vi cng sut raBi 3.10: Thit k bin p xung ngun flyback c p AC in t 90 260Vac, Vout = 5V, Iout = 2A.Bi lmTa chnh lu gi tr in p AC in dng cu diode c ng ra l DC

Gi s chn diode 1N5817 c Vf = 0,5v. Nh vy cn cng sut ng ra bin p l (5+0,5)*2= 11WVi f0 = 50kHz v Vin(min) = 126 VDCL= = Vi Vin(max) = 366 VDCIpk = = 1,016 ALI2 = 3,6.10-3.1,0162 = 3,721 mJ

T hnh => li c kch thc 30x19 mm v AL 520

Ta chn AL chun = 500N = 3,16 = 7,2 Do t l s/th nn s vng th cp l 20,9 Tnh ton cho phn th cp vi N = 7,2Aw cho cun dy c 2 ngn l 0,254 cm2 ng vi li 30x19 theo bng tra T N/AW = 7,2/0,254 = 28

Tra bng: chn dy #14, dy #14 c s vng/cm2 = 34,1

Dy #14 c in tr 2,524/1000feet. Chiu di trung bnh 1 vng vi li 30x19 l 0,204 feet R= NIwrw= 7,2.0,204.0,002524 = 0,0037Vi dng nh Ipk = 1,016A, cng sut mt mt trung bnh(xR)/3 = (1,0162.0,002524)/3 = 0,87 mW #7,9% cng sut ra. Tnh ton cho phn s cp vi N1= 20,9Aw cho cun dy c 2 ngn l 0,254 cm2 ng vi li 30x19 theo bng tra T N/AW = 20,9/0,254 = 82

Tra bng: chn dy #19, dy #19 c s vng/cm2 = 98,4

Dy #19 c in tr 8,046/1000feet. Chiu di trung bnh 1 vng vi li 30x19 l 0,204 feet R= NIwrw= 7,2.0,204.0,008046 = 0,012Vi dng nh Ipk = 1,016/2,9= 0,35A, cng sut mt mt trung bnh(xR)/3 = (0,352.0,008046)/3 = 0,33 mW.3.17: Gii thch hot ng mch khi ng mm cho IC TL494.Thit k mch khi ng mm cho IC TL494, thi gian khi ng mm khong 3s.Bi lma)Hot ng mch khi ng mm cho IC TL494:

in p chn 4 iu khin rng xung ng ra

Mch khi ng mm

Hnh 3.17aMch khi ng mm bt u cho php rng xung u ra tng chm bng cch p dng mt dng sng dc m kim sot u vo thi gian cht(pin 4). Ban u, t Cs s kim sot u vo thi gian cht do p trn t khng t bin tc thi nn p ban u ti chn 4 bng Vref v hiu ha cc kt qu u ra(100 % thi gian cht). Sau t in c np thng qua Rs , rng xung u ra t t tng cho n khi vng iu khin c lnh.Thi gian khi ng mm thng l trong khong t 25 n 100 chu k xung.b)Thit k mch khi ng mm cho IC TL494, thi gian khi ng mm khong 3s.Khi kt thc thi gian khi ng mm, p ti chn 4 c gi tr khong 0.5V(bng 1/10 gi tr Vref).Ta c:

3.18: a) Tm tn s dao dng mch IC TL494 hnh 3.53. b) Mch hnh 3.53 c khi dng mm khng,nu c thi gian khi dng mm khong bao lu?a) Tm tn s dao ng ca mch TL494 hnh 3.53b) Mch hnh 3.53 c khi ng mm khng, nu c th thi gian khi ng l bao lu?

a/ Mch c dng push-pull, tn s hot ng f= b/ Mch c soft-start v c t C3 ni gia cn VREF v chn DT. T lm cho chn DT gim t t in p t mc 5V, lm cho xung PWM ng ra tng dn dn.Thi gian soft-start l thi gian t C3 np ln mc 4.9V.Thi gian soft-start:

Bi 3.20: Tnh li ILmax trong hnh 3.53

Ta thy ng ra l 0.2A, ILmax=0.256A, kt qu ph hp.Bi 3.21:Gii thch hot dng mch cp ngun IC TL494 hnh 3.49,khi ngun cp >40V.

Khi ngun cp Vin > 40V > VZ =39V, th diode zener dn thun, khi BJT c VB = Vin VZ > 1V nn BJT dn, khi in p VCC = VZ + VBE 40V (coi nh VBE 1V), khi VCC 40V tha mn lm ngun cp cho TL494 Tuy nhin xy ra trng hp khi Vin tng n mt gi tr no s lm BJT bo ha khi VCC coi nh ni tt t, mch coi nh ct khi ngun, y l chc nng BJT nh mt kha ngt an ton khi in p tng cao.

Bi 3.22 V s ngun buck s dng IC UC3844

Thit k mch ngun buck Vin = 15V, Vout = 5V.

Chn tn s =100kHz , chn t =1nF suy ra =10K. tn hao trn cun dy khong 20% nn Pout=6W

in p hi tip nga vo o 2.5v nn chn R1, R2 lm cu phn p vi R1=10k, R2=8K2 cng 1 bin tr 5k thun tin trong qu trnh tinh chnh nhm t p ng ra 5v.Ipk=2Iout=2A

Chn Iout=1A nn ng ra i t xung 1N5819, mosfet chn IRF540 tn nhit khng kh v thi gian cht cao.Khi ng mm: chn t 100pF v tr 150k

Bi 3.23: V s ngun boost s dng IC UC3844.S ngun c bn dng Boost:

Tnh ton thng cho mch:1. B dao ng.Tn s dao ng c chn qua cc gi tr nh thi R6 v C3

V d: chn thi gian cht output l 60% Da vo hnh b ta chn C3 = 10uF v f =90kHz Da vo hnh a ta chn R6 = 2k.2. B khuch i sai lch

Trong :VT =& RT =V1 = 2.5in tr hi tip ti thiu cho b khuch i sai lch gii hn bi dng cp ng ra yu cu t mc ghim bng 1V ca b so snh.R9 =3. B so snh nhy dng v cht PWM Dng nh cun dy trong iu kin hot ng bnh thng c kim sot bi in p chn 1. Ipk = V ngng b so snh nhy dng c ngim bn trong l 1V,cho nn dng nh ti a l: Ipk(max) = Thng s mch boost Khi S ng ta c:cun dy np nng lngIpk(max) = (trong Ton =D*T,D l phn trm thi gian cht output, T l chu k) Khi S m ta c: cun dy x nng lngIL Dng IL gim t Ipk(max) ,ta c IL= Ipk(max)

Cho Vin =15V,D = 60%,f =90kHz,RL=10K,L=5mH Vout = 37.5 V V1 = 2.5 Ipk(max)= 0.02 A R4 = 50

3.25/ V s ngun buck nng dng s dng IC TL494.

Dead time = 0s

Trong mch cn c D2 v BT2 xn trn trong qu trnh SW off, in p trn SW vt tng cao nhng khng lm h SW. Tnh ton bin p trong mch:

Ta tnh T hnh 3.26 1mJ dn n tm c li kch thc 26x15 v AL= 250

Tnh ton cun th cp S vng cun th cp

Aw cho cun dy c 2 ngn l 0.202 cm2 ng vi li 26x15 theo bng 3.5 v hnh 3.28

Li c T= 24,73T bng 3.6 ta chn dy #13

Bng 3.6 cho dy #13 c in tr 2,001/1000feet. Chiu di trung bnh 1 vng vi li 26x15 l 0.173 feet theo bng 3.5

R=N2Iwrw= 4,995.0,173.2,001.10-3= 0,0017 Vi dng nh Ipk= 5A, cng sut mt mt trung bnh

Cng sut ra Pout= Vout.Iout= 7,5(W)=> cng sut mt mt chim 0,189% so vi cng sut raBi 3.26: V s ngun flyback s dng IC TL494

Bi lm

Ngun xung kiu : Flybacky l kiu ngun xung truyn cng sut dn tip thng qua bin p. Cho in p u ra ln hn hay nh hn in p u vo. T mt u vo c th cho nhiu in p u raS nguyn l nh sau :

Mch c cu to bi 1 van ng ct v 1 bin p xung. Bin p dng truyn cng sut t u vo cho u ra. in p u ra ph thuc vo bm xung PWM v t s truyn ca liNh chng ta bit ch c dng in bin thin mi to c ra t thng v to c ra sc in ng cm ng trn cc cun dy trn bin p. Do y l in p mt chiu nn dng in khng bin thin theo thi gian do ta phi dng van ng ct lin tc to ra c t thng bin thin.Khi "Switch on " c ng th dng in trong cun dy s cp tng dn ln. Cc tnh ca cun dy s cp c chiu nh hnh v v khi bn cun dy th cp sinh ra mt in p c cc tnh dng nh hnh v. in p s cp ph thuc bi t s gia cun dy s cp v th cp. Lc ny do diode chn nn ti c cung cp bi t CKhi "Switch Off" c m ra. Cun dy s cp mt in t ngt lc bn th cp o chiu in p qua Diode cung cp cho ti v ng thi np in cho tTrong cc m hnh ca ngun xung th ngun Flybach c s dng nhiu nht bi tnh linh hot ca n, cho php thit k c nhiu ngun u ra vi 1 ngun u vo duy nht k c o chiu cc tnh. Cc b bin i kiu Flyback c s dng rng ri trong cc h thng s dng ngun pin hoc acqui, c mt ngun in p vo duy nht cung cp cho h thng cn nhiu cp in p(+5V,+12V,-12V) vi hiu sut chuyn i cao.c im quan trng ca b bin i Flyback l pha(cc tnh) ca bin p xung c biu din bi cc du chm trn cc cun s cp v th cp (trn hnh v)Cng thc tnh ton cho ngun dng FlybackVout=Vin x (n2/n1) x (Ton x f) x (1/(1-(Ton x f)))

vi :n2 = cun dy th cp ca bin pn1 = Cun dy s cp bin pTon = thi gian m ca Q1 trong 1 chu kf l tn s bm xung (T=1/f = (Ton + Toff))Ngun xung kiu Flyback hot ng 2 ch : Ch lin tc (dng qua th cp lun > 0) v ch gin on (dng qua thc cp lun bng 0)

Tnh chn thng s cho mch iu khin:

Tn s dao ng ( Pin 5 & Pin6)Chn dao ng ni bng cch ni RT v CT xung massFosc 1,1/( RT CT)Da vo th chn Fosc suy ra RT v CT

iu khin thi gian cht quyt nh rng xung cc i c khi ng mm (Pin 4)Dng mch vi phn khi ng

t a=//).C B khuchi sai lch iu chnh rng xung (Pin 1, 2,3)

B khuch i sai lch l phng tin cc b khuh i sai lch iu chnh rng xung ng ra t gi tr cc i xung 0, tng ng tm in p ng vo cch chung t 0,3V( Vcc-2V). Dng cm in p v dng in ng ra. Cch hi tip ng ra v khuch i sai lch ( Pin 8, 9, 10, 11) y ta thit k s dng dng n tng bng cch ni PIN 13 xung mass.

rng xung PWM bin thin trn l thuyt t 0-96% Ngun cp cho TL494 ( Pin 12 & Pin 7)

Mch gii hn ngun cp cho TL494 Vcc< 40V Mch bo v qu dng ( Pin15 & Pin 16)

Mch ng dng: Vin 220v AC, Vo= 5VDC, I0 = 10A Mch ngun

Phi m bo ngun cp cho IC TL494 Vcc t 7V-40V. Ta c th gn thm linh kin bo v p cp ngun cho TL494 cu phn p R3, R4 l ng vo cho b khuch i sai lch ng (-) l 2.5V. Cu phn p R8, R9 dng iu chnh rng xung PWM. Tr R7 hn dng vo OPAMP khi mch xy ra qu dng Mch bo v qu dng ( Pin15 & Pin 16)Ta c: IL max = 1,5A. Ngun c kh nng chu dng 10ADng bo v Isc = Io + = 10 + 1,5 = 10,75A

R1, R2 khong 1V gii hn dng vo ca OPAMP. Khi xy ra qu dng Pin 15 =1v R13 = = 0,1 iu khin thi gian cht quyt nh rng xung cc i c khi ng mm (Pin 4)

T C2 cho php ng ra l 5V vi 100% thi gian cht. thng thng ta chn gi tr in p ti chn 4 lc khi ng l 1/9 gi tr max= 0,56v Chn cu phn p R6, RT t l l 1:10t= = = 50us C2 = = = 2,5uF Mch n dng v lc nhiu ng ra

Chn t ng ra Ni tr ca t :

in dung phi ln duy tr in p ng ra: Kha cng sut dng BJT ghp lin tng

I0max ca IL494 khong 250mA nn ta cn phi ghp thng qua BJT khuch i dng ng ra. Ta chn ghp darlington BJT NTE153 v NTE331 li ng ra bi dng 144mA t IC TL494. R11, R12 hn dng cho BJT khi trng thi OFF hFE(Q1) ti Ic = 3A l 15 hFE(Q2) ti Ic = 10A l 5 iB 144mAChn R10 bi

Chn R10 = 220 iB ta dng mch khuc i khng o.

Dng IL max c tnh nh sau:

vi IL=2A, Vref=5V, chn R8=0.5 Ohm, R10=100 Ohm suy ra c R9=400 Ohm.Bi 3-29: Yu cu thit k mch ngun n p xung Ngun Input 12 VDC = 9.6V - 14.4V Output -5VDC/2A V c bo v qu dng 2AV Output m, nn ta s s dng mch buck-boost, c s khi:

Ta s dng TL494, s khi nh hnh:

Nhng thng s in vo cc gi tr th nhm em vn cha hon thnh c, mong thy thng cm

Bi 32: Thit k mch n p xung in p vo 24V. in p ra 48 V v 5VTa thit k mch nh s sau

Phng php hi tip cch ly hon ton ng GND gia ng ra v IC iu khin. Diode optocoupler c iu khin bi dng qua TL431 IAK, t iu khin dng Ic transistor lm Vfb tang, IC iu khin tc ng lm rng xung hp li, ng ra Vo s gim li.Rb v Cb tang tc p ng nhanh cho optocoupler.Cch kt ni to hi tip trong trng hp c 2 ng ra +5V v + 48V. hai ngun ra +5V v +48V c cng li qua R3 v R4 phn cc cho chn G TL431. m bo c 2 ngun p ng ra u n nh khng ph thuc vo ti ca ngun khc. Ng ra +48V to thnh t cch chng p, cun L1 v D1 to ngun +5V, cun L2 v D2 to ngun p +43V xp chng ln ngun +5V.