Design and Application Notes for AP3765 System Solution

Transcription

1 licaio oe 064 Desig ad licaio oes for 3765 ysem oluio reared by u Ju Jie ysem Egeerg De.. roducio The 3765 uses ulse Frequecy Modulaio (FM) mehod o realize Discouous Coducio Mode (DCM) oeraio for flyback ower sulies. The rcile of FM is differe from ha of ulse Widh Modulaio (WM), so he desig of rasformer is also differe. The 3765 ca rovide accurae cosa volage, cosa curre (C/CC) regulaio by usg rimary ide egulaio (). The 3765 ca also achieve ulra-low sadby ower due o is FM oeraio ad a ovaive ulra-low saru curre echique. ess ha 30mW sadby ower ca be obaed o mee five-sar charger crieria wih 3765 sysem soluio. yical 3765 alicaio circui is show Figure.. eraio Descriio. Cosa rimary eak Curre The rimary curre i() is sesed by a curre sese resisor as show Figure. The curre rises u learly a a rae of: di() vg() = () d M T D + C 5 C3 + C4 + C D s + D3-3 CC UT 3765 Q 6 FB C FB 4 GD 7 Figure. Tyical chemaic of 3765 oluio Ju. 0 ev.. BCD emicoducor Maufacurg imied

2 licaio oe 064 Figure. rimary Curre Waveforms s illusraed Figure, whe he curre () rises u o K, he swich Q urs off. The cosa eak curre is give by: C = () The ouu volage is differe from he secodary volage a diode forward dro volage ha deeds o he curre. f he secodary volage is always deeced a a fixed secodary curre, he differece bewee he ouu volage ad he secodary volage will be a fixed d. For 3765, he volage deecio o is a 3.µs of he D o-ime, which meas he he secodary volage is deeced a a fixed secodary curre. The C loo corol fucio of 3765 he geeraes a D off ime o regulae he ouu volage..3 Cosa Curre eraio The eergy sored he mageizg ducace M each cycle is herefore: Eg = M (3) o, he ower rasferrg from u o ouu is give by: = M f (4) W Where he f W is he swichg frequecy. Whe he eak curre K is cosa, he ouu ower deeds o he swichg frequecy f W.. Cosa olage eraio The 3765 caures he auxiliary wdg feedback volage a FB ad oeraes cosa volage (C) mode o regulae he ouu volage. ssumg he secodary wdg is maser, he auxiliary wdg is slave durg he D o-ime ad he auxiliary volage is give by: ( + ) UX o d UX = (5) where he d is he diode forward dro volage. UX is he urs of auxiliary wdg, ad is he urs of secodary wdg. Figure 4. ecodary Curre Waveform CC oeraio, he CC loo corol fucio of 3765 will kee a fixed roorio bewee D o-ime ad D off-ime FF by dischargg or chargg he buil- caaciace coeced. The fixed roorio is 4 = (6) 3 FF The relaioshi bewee he ouu cosa curre ad secodary eak curre s is give by: ou = s (7) + FF he sa of D ur-o, he rimary curre rasfers o he secodary a a amliude of: s = (8) s Thus he ouu cosa-curre is give by: ou = = (9) s + 7 s FF Figure 3. uxiliary olage Waveform Ju. 0 ev...4 eadg Edge Blakg Whe he ower swich is ured o, a ur-o sike will occur o he sese-resisor. To avoid false ermaio of he swichg ulse, a 750s leadg BCD emicoducor Maufacurg imied

3 licaio oe 064 edge blakg is buil. Durg his blakg eriod, he curre sese comaraor is disabled ad he gae driver ca o be swiched off..5 CCM roecio The 3765 is desiged o oerae Discouous Coducio Mode (DCM) boh C ad CC modes. To avoid oerag Couous Coducio Mode (CCM), he 3765 deecs he fallg edge of he FB u volage o each cycle. f a fallg edge of FB is o deeced a he ed of, he 3765 will so swichg..6 & Ck The 3765 cludes over-volage roecio () ad oe circui roecio (Ck) circuiries as show Figure 5. f he volage a FB exceeds 8, 00% above he ormal deecio volage, he 3765 will eer mode. However, if he 3765 does moior risg edge of FB u a he ed of or high volage (>0.075) afer ME, i will eer Ck mode. Whe 3765 eers or Ck mode, i will seds ou a faul deecio ulse every 8ms uil he faul has bee removed CM Ck CM Timer_8ms Figure 5. & Ck Fucio Block 3. Desig Guideles 3. ow adby ower Desig Q ro o The radeoff bewee he low sadby ower ad he ouu overshoo a o load should be cosidered durg he selecio of he dummy resisor 8. order o achieve less ha 30mW sadby ower while havg a acceable ouu volage rise a o load, 5.K o 0k is recommeded for 8. The ower cosumed he saru resisors (+) also becomes cosiderable o load or ligh load codiios. o 0MΩ o 3MΩ resisace is recommeded for he sum of ad cosiderg he arge of less ha 30mW sadby ower ad less ha 3s ur-o delay ime. d he bias caacior C is recommeded as µf o.5µf accordgly. 3.. Trasformer Desig Figure describes a flyback coverer corolled by 3765 wih a 3-wdg rasformer---rimary wdg ( ), ecodary wdg ( ) ad uxiliary wdg ( ) for bias ower ad ouu volage deecg. The 3765 seses he auxiliary wdg feedback volage a FB ad obas ower suly a CC. Figure 6, a series of relaive ideal oeraio waveforms are give o illusrae some arameers used followg desig se. d he omeclaure of he arameers Figure 6 is as he followg: dri ---a simlified drivg sigal of rimary rasisor ---he rimary side curre ---he secodary side curre ---he secodary side volage sw ---he swichg eriod of frequecy f sw ---he swichg frequecy o ---he ime of rimary side os- ---he ime of secodary side off ---he discouous ime ---eak curre of rimary side s ---eak curre of secodary side ds ---he sum of o ad he forward volage dro of recificaio diode dri sw s s os ds s off Figure 6. eraio Waveforms Ju. 0 ev.. BCD emicoducor Maufacurg imied 3

4 licaio oe Desig e: e. elec a easoable for he Flyback Coverer wih Calculae he Maximum Tur aio of XFM The maximum ur raio of rasformer should be desiged firs, which is o esure ha he sysem should work DCM all workg codiios, esecially a he mimum u volage ad full load. f he sysem ca mee equaio (0) a mimum u volage ad full load, i ca work DCM all workg codiios. + (0) W For he rimary side curre, = () dc Where is he ducace of rimary wdg. dc is he recified DC volage of u. Whe dc is he mimum value, he maximum ca be obaed. o, _ MX = () dc _ m For he secodary side curre, = (3) s (3), s is he ducace of secodary wdg. = +, d d is he forward volage dro of he secodary diode. For (3), C regulaio, he s is a cosa volage, so is a cosa value wih differe u volage. he flyback coverer, whe he rimary rasisor urs, he eergy is sored he mageizg ducace. o he ower sored is give by, = f (4) W The, W = (5) W, ad (0) are relaced wih (5), () ad (3), s s + (6) s dc_m Because he eak curre ad ducace of rimary side ad secodary side have he followg relaioshi, = (7) s s = (8) Where is he ur raio of rimary wdg o he secodary wdg. Wih (6), (7) ad (8), he, Because, + (9) = (0) η Where η is he sysem efficiecy. maximum load, he sysem will work he boudary bewee C ad CC sages. ca be give by, = () s W The, s ca be defed, s = k () he desig of 3765, W k = = 3.5 ( CC mode, he roorio of ad FF is 4:3) (3) o i ca be obaed, Ju. 0 ev.. BCD emicoducor Maufacurg imied 4

5 licaio oe 064 k η dc_m( ) (4) Therefore, he maximum ur raio of rimary ad secodary side ca be obaed. k η dc_m( ) (5) + Because above calculaios are all based o ideal codiios wihou cosiderg recisio of sysem, k is give a exerieial value 3.85 o relace he real value Calculae he eak Curre of rimary ide ad Curre esed esisor ca be calculaed by he ouu curre. k d s = = (6) Here, k=3.85 is he calculaed value of MX. 3765, 0.5 is a eral referece volage. f he sesed volage C reaches 0.5, he ower rasisor will be shu dow ad will be eded. 0.5 C = (7) o C ca be obaed from equaio (7) ad seleced wih a real value from he sadard resisor series. fer C is seleced, should be modified based o he seleced C. From ow o, ad C have bee desiged. e. Desig Trasformer -. Calculaio of he rimary ide ducace --- The rimary side ducace is relaive wih he sored eergy. should be big eough o sore eough eergy, so ha o_max ca be obaed from his sysem. From formula (0), he ouu ower ca be give by, = fwη (η: sysem efficiecy) (8) The, ca be go by, = (9) f η K W Here, o achieve good overall sysem erformace, he oimum swichg frequecy f W is recommeded o be 50kHz o 60kHz uder full oad. -. e-calculae he Tur aio of rimary ad ecodary ides--- From formula (6), he ur raio of rimary ad secodary side ca be re-calculaed. k = (k 3.85) (30) = -3. Calculae he Turs of rimary, ecodary ad uxiliary ides Firs, he reasoable core-ye ad B should be seleced. The, he urs of 3-wdg rasformer ca be obaed resecively. The urs of rimary wdg, 4 K0 = ( :mh, :m,e:mm, B :G) e B The urs of secodary wdg, (3) = (3) The urs of auxiliary wdg, = (33) Here, ca be se a yical value of 0. s is equal o o+ d. e ca be go auomaically afer core-ye is seleced. e 3. elec Diode ad rimary Trasisor 3-. elec Diodes of ecodary ad uxiliary ides Maximum reverse volage of secodary side + dc_max dr = (34) Ju. 0 ev.. BCD emicoducor Maufacurg imied 5

6 licaio oe 064 Maximum reverse volage of auxiliary side, + dc_max dar = (35) (34) ad (35), he maximum DC u volage should be used. 3-. elec he rimary ide Trasisor + dc_max = dc_sike + (36) dc_max Be careful ha he value of dc_sike will be varied wih differe subber circui.. 5. Desig Examle ecificaio: u volage: 85 C -65 C uu volage: =5 uu curre: =0.7 ysem Efficiecy: 75% wichg frequecy: f W =60kHz Forward volage of secodary diode: d =0.4 Forward volage of auxiliary diode: da= Feedback volage of auxiliary wdg: a=0 Core_ye: EE6 (e=9.mm ) B : B =450G dc_sike =00 (wih subber circui) uu cable: 8WG,.5m log, 0.4Ω/m ecodary diode urs o duy cycle: D os = 4/7 Feedback resisor: 6=36.5k, 7=9.k Desig e: e. easoable of Flyback wih 3765 hould be Desiged -. Calculae he Max. Tur aio of XFM MX k η = dc_m( )(k 3.85) (37) + dc_m = ac_m 40 ( whe =0.7, e: dc dro abou 40 ) (38) MX = 8.3 (39) -. Calculae he eak Curre of rimary ide ad Curre esed esisor d s k = = (40) _max = 35m (4) esed curre resisor, 0.5 C = (4) C. 538Ω (e: C =. 54Ω ) (43) e-calculae eak curre of rimary side, _max = 35m (44) e. Desig Trasformer -. Calculaio of he ducace of rimary ide--- = (45) f η K W =.47mH (46) -. e-calculae he Tur aio of rimary ad ecodary ide--- k = (k 3.85) (47) = 8.3 (48) -3. Calculae he Turs of rimary, ecodary ad uxiliary ides The urs of rimary wdg, 4 K0 = (49) e B =0 (50) The urs of secodary wdg, = (5) = T (5) Ju. 0 ev.. BCD emicoducor Maufacurg imied 6

7 licaio oe 064 The urs of auxiliary wdg, = (53) = 44T (54) e 3. elec Diode ad rimary Trasisor 3-. elec Diodes of ecodary ad uxiliary ides Maximum reverse volage of secodary side + dc_max dr = (55) dr = 49. (56) Maximum reverse volage of auxiliary side dc_max dar = + (57) dar = 8.8 (58) 3-. elec rimary ide Trasisor dc_max = dc_sike + dc_max + (59) dc_max = 50.9 (60) e 4. elec easoable Feedback esisor 6 ad 7 7 FB = 4 = a (e:7=9.kω,6=36.5kω) (6) Desig esuls ummary:. Calculae he Maximum eak Curre of rimary ide ad C K = 35 m eak curre of rimary side C =.54 Ω Curre sesed resisor. Desig Trasformer =.47 mh(±8%) ducace of rimary side = 8.3 Tur raio of rimary ad secodary = 0 T Turs of rimary side = T Turs of secodary side = 44 T Turs of auxiliary side 3. elec Diode ad rimary Trasisor dr= 49. Maximum reverse volage of secodary diode dar= 8.8 Maximum reverse volage of auxiliary diode dc_max= 50.9 olage sress of rimary rasisor 4. elec Feedback esisor 6= 36.5 kω Feedback resisor 7= 9. kω Feedback resisor Ju. 0 ev.. BCD emicoducor Maufacurg imied 7