Application Notes for AP3770 System Solution

Transcription

1 lcaon oe 1067 lcaon oes for 3770 ysem oluon reared by u Qg Hua ysem Engeerg De. 1. nroducon The 3770 uses ulse Frequency Modulaon (FM) mehod o realze Dsconuous Conducon Mode (DCM) oeraon for FYBCK ower sules. The rcle of FM s dfferen wh ha of ulse Wdh Modulaon (WM), so he desgn of ransformer s also dfferen. The 3770 can rovde accurae consan volage, consan curren (C/CC) regulaon by usg rmary de egulaon () has he secal echnque o suress he audo nose, ernal le comensaon o reduce he number of sysem comonens, fxed cable comensaon o comensae he volage dro on dfferen ouu cable for achevg good C regulaon. The 3770 can acheve low sandby ower less han 30mW. Fgure 1. 5/1 uu for Baery Charger of Moble hone Fgure 1 s 3770 ycal alcaon crcu, whch s a FYBCK converer conrolled by 3770 wh a 3-wdg ransformer---rmary wdg (), econdary wdg (s) and uxlary wdg (a). The 3770 senses he auxlary wdg feedback volage a FB and obas ower suly a CC. Fgure s he ycal oeraon waveforms of FM conroller. n hs fgure, a seres of relave dea oeraon waveforms are gven o llusrae some arameers used followg desgn ses. nd he nomenclaure of he arameers Fgure s llusraed. e. 011 ev dr --- smlfed drvg sgnal of rmary ranssor ---The rmary sde curren s ---The secondary sde curren EC ---The volage of secondary W ---The erod of swchg frequency ---The me of rmary sde ---The me of secondary sde FF ---The dsconuous me FF --- The me of secondary sde ff K ---eak curren of rmary sde K ---eak curren of secondary sde ---he sum of o and forward volage of recfcaon dode BCD emconducor Manufacurg med 1

2 lcaon oe 1067 dr W K K EC FF FF Fgure. eraon Waveforms. Fve secs for ysem Desgn 1. ow andby ower Desgn. wchg Frequency Desgn 3. Transformer and ower Devces Desgn 4. Feedback essors Desgn 5. e Comensaon Desgn.1 ow andby ower Desgn Zero-aru-Curren echnque, he saru u ressors 3+4 should be hgher o 10M o 14MΩ o furher lower he ower loss. The recommended value of dummy load ressor 13 s 4.7KΩ o 10KΩ for an model wh 5 ouu volage. The selecon of dummy load ressor s a radeoff beween sandby ower and - Curve.. wchg Frequency Desgn n order o acheve low sandby ower, 3770 decreases he mmum oerag volage. nd due o roreary H 0.5 C_EF 1.4 CC f W 47.6kHz f W 0kHz 4% Fgure 3. elaonsh Beween CC, f W and wh Consan eak Curren e. 011 ev BCD emconducor Manufacurg med

3 lcaon oe 1067 When he consan eak curren s adoed, he volage of CC s creased learly wh load creasg. The maxmum value of CC s equal o W 4 DD (1) 10 The rmary curren () s sensed by a curren sense ressor C as shown Fgure. The ower ransferrg from u o ouu s gven by: Where, he f W s he swchg frequency. When he eak curren K s consan, he ouu ower deends on he swchg frequency f W. f W s learly creased wh load creasg. n 3770, wo-segmened eak curren s used o realze audo nose suresson. The eak curren s abou 0.5 when >4% max, and he eak curren s abou 0.5/1.5 when <4% max. 1 f () W D CC H /1.5 C_EF 0.4х _MX _MX f W 55kHz 5kHz f W 3.1kHz 3.85kHz 0kHz 0.4х _MX _MX UCE /3* UCE 0.4х _MX _MX Fgure 4. elaonsh Beween CC, f W and wh arable eak Curren o, he volage of CC and swchg frequency has a muaon a abou 4% of load. he muaon o, f he eak curren s changed from 0.5( hgh K ) o 0.33(low K ), he volage of CC a low K wll be creased o 1.5 mes of CC a hgh K and he swchg frequency f W a low K wll be creased o.5 mes of f W a hgh K. o he range of load workg he audo frequency s suressed. H 0.5 C_EF 0.5/1.5 39% 4% Fgure 5. Hyseress a Converson Beween ow K and Hgh K e. 011 ev BCD emconducor Manufacurg med 3

4 lcaon oe 1067 n order o avod oscllaon, a hyseress s added a he converson beween low K and hgh K. Consderg he relaonsh beween audo nose and flux densy of ransformer, delab 500 gauss s beer for audo nose suresson. all workg condons. + W FF For he rmary sde curren, (7) The low lmaon of maxmum swchg frequency s gven by audo nose suresson. nd he uer lm of he 3770 can be u o 10kHz. Bu hs s only he lm of he C; he fally desgned maxmum swchg frequency s deermed by he radeoff beween he effcency, mechancal dmensons and hermal erformance..3 Transformer and ower Devces Desgn n Consan Curren oeraon of 3770, he CC loo conrol funcon of 3770 wll kee a fxed rooron beween D1 ( Fgure 1) on-me and D1 off-me FF ( Fgure ) by dschargg or chargg a caacor embedded he C. The fxed rooron s 4 (3) 6 FF The relaonsh beween he ouu consan-curren and secondary eak curren K s gven by: 1 s (4) + FF he san of D1 urn-on, he rmary curren ransfers o he secondary a an amlude of: s (5) Thus he ouu consan-curren s gven by: 1 1 (6) + FF 5 Desgn es: e 1, a reasonable K of FYBCK wh 3770 should be desgned 1-1. Calculae he Max. urn rao of XFM The maxmum urn raon of XFM should be desgned frs, whch s o ensure ha he sysem should work DCM all workg condons, esecally a he m. u volage and full load. s we know, f he sysem can mee equaon (7) a mmum u volage and full load, can work DCM (8) dc Where s he ducance of rmary wdg. dc s he recfed DC volage of u. When dc s he mmum value, he maxmum can be obaed. o, _MX (9) dc _ m For he secondary sde curren, s (10) n (10), s he ducance of secondary wdg. +, d s he forward volage of secondary dode. d For (10), C regulaon, he s a consan volage, so s a consan value wh dfferen u volage. n FYBCK converer, when he rmary ranssor urns, he energy sored he magnezg ducance. o he ower ransferrg from he u o he ouu s gven by, ' η η (11) ' 1 f (1) W Here, ' s u ower of ransformer, no cludg he all of he ower loss a rmary sde (ecfer, CD snubber, BJT and so on). η s defon o he u effcency of sysem, whch s abou 0.9. Then, W η (13) W, and (7) are relaced wh (13), (9) and (10), η s s + s dc_m (14) e. 011 ev BCD emconducor Manufacurg med 4

5 lcaon oe 1067 Because he eak curren and ducance of rmary sde and secondary sde have he followg relaonsh, η (15) s s Here, s he urn rao of rmary and secondary sdes. Wh (14), (15) and (16), hen, η 1 + η Because, (16) (17) (18) η η s he sysem effcency. full load, he sysem wll work he boundary of CC regulaon. can be gven by, 1 (19) s W Then, K can be defed, k (0) s n he desgn of 3770, k W 5 (1) The followg can be obaed, dc_m k η η ( η η + d ) () 1-. Calculae he eak curren of rmary sde and curren sensed ressor K can be calculaed by he ouu curren. s k η (3) Here, k5, η 0. 9, whch s he effcency of K and K. s he calculaed value of max. n 3770, 0.5 s an ernal reference volage. f he sensed volage C reaches 0.5, he ower ranssor wll be shu down and wll be ended. 0.5 C (4) o C can be obaed from (4) and seleced wh a real value from he sandard ressor seres. fer C seleced, K should be modfed based on he seleced C. From now on, K and C have been desgned. e, Desgn Transformer -1. Calculae he ducance of rmary sde--- The rmary sde ducance s relave wh he sored energy. should be bg enough o sore enough energy, so ha _Max can be obaed from hs sysem. From formula (18), he ouu ower can be gven by, 1 η fw (5) η Where f W was se by he user based on defe requremen. Then, can be goen by, η (6) f η K W -. e-calculae he urn rao of rmary and secondary sde--- From formula (4), he urn rao of rmary and secondary sde can be re-calculaed. k (k 5 ) η (7) -3. Calculae he urns of rmary, secondary and auxlary sdes Frs, he reasonable core-ye and B should be seleced. Then, he urns of 3-wdg ransformer can be obaed resecvely. The urns of rmary wdg, K (8) e B The urns of secondary wdg, (9) The urns of auxlary wdg, (30) e. 011 ev BCD emconducor Manufacurg med 5

6 lcaon oe 1067 Where CC + da, CC s he se C suly volage and da s he volage dro of he auxlary dode. For 3770, he ycal value of U s decreased o 5.5, so he suly volage of C, CC can be se o a ycal value---1. s equal o + d. e can be goen auomacally afer core-ye s seleced. -4. Check he maxmum duy cycle of rmary sde fer urn rao of rmary sde and secondary sde s desgned, he maxmum duy cycle of rmary sde a low le volage can be calculaed aga. Consderg he ol-second balance beween magnezg and de-magnezg, he formula of duy cycle s D ( + ) 0.4 d (31) dc e 3, elec dode and rmary ranssor 3-1. elec dodes of secondary and auxlary sdes Maxmum reverse volage of secondary sde, dc_max dr + (3) Maxmum reverse volage of auxlary sde, dar + dc_max (33) n (3) and (33), he maxmum DC u volage should be used. 3-. elec he rmary sde ranssor dc_max dc_ske + dc_max + (34) Be careful ha he value of dc_ske wll be dfferen wh dfferen snubber crcu. Desgn Examle: ecfcaon: nu volage: 85 C o 65 C uu volage: 5.3 (Consderg he cable comensaon) uu curren: 1.1 Effcency: 80% s hgher han he oal effcency because he loss he u recfer and he BJT are no cluded. her seg by users: wchg frequency: f W 54kHz (hould be equal o or hgher han 54kHz) Forward volage of secondary dode: d0.4 Forward volage of auxlary dode: da1.1 CC volage: CC 1 Core_ye: EE16 (e19.mm ) e B : B <3000G dc_ske 100 (wh snubber crcu) Desgn es: e 1, a reasonable K of FYBCK wh 3770 should be desgned Calculae he maxmum urn rao of XFM k η η MX dc_m ( )(k 5 ) η η + dc_m 40, η 0.75, η 0. 9, η 0. 9 ac_m d (35) MX (36) The urn rao s fally seleced as: Calculae he eak curren of rmary sde and curren sensed ressor s k η ( η 0. 9, whch s he ransfer effcency of and s) _max 330m (37) ensed curren ressor, C 0.5 (38) 359m C _ max C 1.5Ω (39) e-calculae eak curren of rmary sde, _max 333m (40) e, Desgn Transformer -1. Calculae he ducance of rmary sde--- η (41) f η K W.035mH (4) e. 011 ev BCD emconducor Manufacurg med 6

7 lcaon oe e-calculae he urn rao of rmary and secondary sde--- k (k 5 ) η (43) 18.3 (44) -3. Calculae he urns of rmary, secondary and auxlary sdes The urns of rmary wdg, K (45) e B > 118T (46) The urns of secondary wdg, (47) 7T ecalculae he rmary wdg, (48) (49) 18T (50) The urns of auxlary wdg, + o d (51) 15T (5) -4. Check he maxmum duy cycle of rmary sde The maxmum duy cycle of rmary sde s calculaed as followg, ( + d ) 0.4 D dc (53) ( + d ) 0.4 ( ) D dc 0.58 _ m dc _ m 80 (54) e 3, elec dode and rmary ranssor 3-1. elec dodes of secondary and auxlary sdes Maxmum reverse volage of secondary sde, dr dc_m ax dr + dc_max Maxmum reverse volage of auxlary sde, dar + dc_max dar elec rmary sde ranssor dc_max d c _ max dc_ske + dc_max * (55) (56) (57) (58) (59) (60) (61) Desgn esuls ummary: 1.Calculae he maxmum eak curren of rmary sde and C K 333 m eak curren of rmary sde C 1.5 Ω Curren sensed ressor.desgn ransformer mh(+/-8%) nducance of rmary sde 17 Turn rao of rmary and secondary 18 T Turns of rmary sde 7 T Turns of secondary sde 15 T Turns of auxlary sde D MX 0.5 Maxmum duy cycle of rmary sde a DC elec dode and rmary ranssor dr 8 Maxmum reverse volage of secondary dode dar 56 Maxmum reverse volage of auxlary dode dcmax 567 olage sress of rmary ranssor e. 011 ev BCD emconducor Manufacurg med 7

8 lcaon oe Feedback essors Desgn Fgure 6. Feedback essors Crcu From above Fgure 6, o FB ( FB1 + FB FB ) D (6) Through adjusg FB1 and FB, a suable ouu volage can be acheved. The recommended values of FB1 and FB are wh 5kΩ o 50kΩ..5 e Comensaon Desgn The ernal le comensaon funcon 3770 s shown Fgure 7. 1 s closed when he rmary swch s. The le volage can be deeced from he FB. The deeced volage ernally comensaes he eak curren. o he le comensaon s deermed by E. n dfferen alcaon, he value of E s dfferen. Fgure 7. e Comensaon Crcu e. 011 ev BCD emconducor Manufacurg med 8

9 lcaon oe 1067 W FB FF Fgure 8. Waveform of FB The negave volage of FB ( Fgure 8) s lear o le volage. The 3770 samles o realze he le comensaon. FB + FB1 FB a dc (63) The comensaed volage of le comensaon ( C_E ) can be calculaed by he followg formula, cs _ le le 1 K 670k k le FB + FB1 FB a dc (64) o, E can be adjused o acheve excellen le regulaon of ouu curren. 3. ummary n order o ge good erformance of 3770, s moran o desgn ransformer, le comensaon and feedback ressance correcly. Ths alcaon only gves a relmary desgn gudele abou hese asecs and consders deal condons, so some arameers need o be adjused slghly on he bass of he calculaed resuls. e. 011 ev BCD emconducor Manufacurg med 9