Application Notes for AP3771 System Solution

Transcription

1 lcaon oe 1074 lcaon oes for 3771 ysem oluon reared by Zhao Jg Jg ysem Engeerg De. 1. nroducon The 3771 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 3771 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 3771 can acheve low sandby ower less han 30mW. T1 D 5 C3 C1 T1 D1 C s C4 DUMMY T D3 - C5 CC C GTE 3771 CC FB Q1 FB1 a GD FB E cs Fgure 1. Tycal lcaon Crcu of 3771 for daer Fgure 1 s 3771 ycal alcaon crcu, whch s a FYBCK converer conrolled by 3771 wh a 3-wdg ransformer---rmary wdg (), econdary wdg (s) and uxlary wdg (a). The 3771 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 deal oeraon waveforms are gven o llusrae some arameers used followg desgn ses. nd he nomenclaure of he arameers Fgure s llusraed. dr --- smlfed drvg sgnal of rmary MFET EC ---The ransen volage of secondary ---he sum of and forward volage of recfcaon dode ---The rmary sde curren s ---The secondary sde curren K ---eak curren of rmary sde K ---eak curren of secondary sde 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 BCD emconducor Manufacurg med 1

2 lcaon oe 1074 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 n order o acheve low sandby ower, 3771 decreases he mmum oerag volage. n order o acheve he lower ower loss erformance, he saru ressor T1 T should be as hgh as ossble on he remse of meeg urn on delay me requremen. The selecon of dummy load ressor s a radeoff beween sandby ower and - Curve.. wchg Frequency Desgn H 0.5 C_EF 1.4 CC f W 47.6kHz f W 0kHz 4% Fgure 3. elaonsh Beween CC, f W and a Consan eak Curren Mode BCD emconducor Manufacurg med

3 lcaon oe 1074 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) 8 75 The rmary curren (), as shown Fgure, s sensed by a curren sense ressor C. The ower ransferrg from u o ouu s gven by: 1 f η () W Where, he f W s he swchg frequency. η s he effcency of he sysem. 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 3771, 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. 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 a arable eak Curren Mode o, he volage of CC ( CC ) and swchg frequency (f W ) has a lea a abou 4% of load. he lea 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 BCD emconducor Manufacurg med 3

4 lcaon oe 1074 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. The low lmaon of maxmum swchg frequency s gven by audo nose suresson. nd he uer lm of he 3771 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 3771, he CC loo conrol funcon of 3771 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) 4 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 Calculae he Max. urn rao of XFM ( MX ) The maxmum urn rao 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 under all workg condons. (7) W For he rmary sde curren, (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 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) Because he eak curren and ducance of rmary sde and secondary sde have he followg relaonsh, η (15) s BCD emconducor Manufacurg med 4

5 lcaon oe 1074 s (16) Here, s he urn rao of rmary and secondary sdes. η 0.95, whch s he effcency of K and K. Wh (14), (15) and (16), hen, η 1 η Because, (17) (18) η η s he sysem effcency from u o ouu. 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 3771, W k 4 (1) The followg can be obaed, k η max η dc_m ( ) () η η Then s fxed as less han or equal o MX..3. Calculae he eak curren of rmary sde and curren sensed ressor ( K & C ) K can be calculaed by he ouu curren. s k η (3) Here, k4, η 0. 9, whch s he effcency of K and K. n 3771, 0.5 s an ernal reference volage. f he sensed volage C reaches 0.5, he ower MFET 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. We recommend d usg 1% olerance ressors for C. fer C s seleced, K should be modfed based on he seleced C. From formula (3), he urn rao of rmary and secondary sde can be re-calculaed. k (k 4 ) η.3.3 Calculae he ducance of rmary sde--- (5) The rmary sde ducance deermes he sored energy. should be bg enough o sore enough energy, so ha _Max can be obaed frs, from he sysem verson. From formula (18), he ouu ower can be gven by, 1 η f W (6) η Where f W was se by he user based on defe requremen. Then, can be goen by, η (7) f η K W.3.4 Calculae he urns of rmary, secondary and auxlary The urns of rmary wdg, K K (8) e B e B max Frs, he reasonable core-ye and B should be seleced. e can be goen auomacally afer core-ye s seleced. s we know, (9) nd he urns of auxlary wdg, (30) Where, s equal o d. CC da, CC s he se C suly volage and da s he volage dro of he auxlary dode. For 3771, he ycal value of U s decreased o 6.5, so he suly volage of C,CC can be se o a ycal value Check he maxmum duy cycle of rmary sde fer urn rao of rmary sde and secondary sde s BCD emconducor Manufacurg med 5

6 lcaon oe 1074 desgned, he maxmum duy cycle of rmary sde a low le volage can be calculaed aga. MX k η η dc_m ( ) η η d (35) Consderg he ol-second balance beween magnezg and de-magnezg, he formula of duy cycle s D ( ) 0.5 d (31) dc.3.6 elec dodes of secondary and auxlary sdes dc_m 40, ac_m We choose 11 ) Calculae he eak curren of rmary sde and curren sense ressor ( K & C ) 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..3.7 elec he rmary sde MFET s k η η We choose C C K cs _ ref 0.85Ω, 0.64, ) Calculae he ducance of rmary sde--- (36) (37) (38) (39) dc_max dc_ske dc_max (34) Be careful ha he value of dc_ske wll be dfferen wh dfferen snubber crcu. Desgn Examle 1 (for 1/1 daer lcaon) ecfcaon: nu volage: 90 C o 64 C uu cable: _CBE 1 uu curren: 1 uu CB, 1.3 (wh 1.8m WG4 cable) k* T W /T 4 Effcency: η 0. 9 her seg by users: wchg frequency: f W 60kHz Forward volage of secondary dode: d 0.4 Forward volage of auxlary dode: da 1.1 CC volage: CC 18 Core_ye: EE19/16 (e.4mm ), Bmax<3000G dc_ke 50 (wh snubber crcu) Desgn es: 1) Calculae he maxmum urn rao of XFM η 1. 15mH (40) f η K W We choose 1.15mH 4) Calculae he urns of rmary, secondary and auxlary sdes (,, ) K K e B e B max (41) 110 s ) Check he maxmum duy cycle of rmary sde (4) (43) The maxmum duy cycle of rmary sde s calculaed as followg, ( d ) 0.4 D 0.55 (44) dc 6) elec dodes of secondary and auxlary sdes Maxmum reverse volage of secondary and auxlary sde, BCD emconducor Manufacurg med 6

7 lcaon oe 1074 dc_max dr (45) dc_m ax 65 (46) dc_max (47) dr 47 dc_max da r 70 (48) 7) elec rmary sde MFET dc_ske dc_max (49) ds_mos 564 Desgn esuls ummary: 1.Calculae he maxmum eak curren of rmary sde and C K 640 m eak curren of rmary sde C 0.85 Ω Curren sensed ressor.desgn ransformer 1.15 mh nducance of rmary sde 11 Turn rao of rmary and secondary 110 T Turns of rmary sde 10 T Turns of secondary sde 15 T Turns of auxlary sde D MX 0.55 Maxmum duy cycle of rmary sde a DC elec dode and rmary ranssor dr 47 Maxmum reverse volage of secondary dode dar 70 Maxmum reverse volage of auxlary dode dcmax 564 olage sress of rmary ranssor Desgn Examle (for 1/1.5 daer lcaon) MX k η η dc_m ( ) η η d (50) ecfcaon: nu volage: 90 C o 64 C uu cable: _CBE 1 uu curren: 1.5 uu CB, 1.4 (wh 1.5m WG cable) k*t W /T 4 Effcency: η 0. 75, η 0. 9, η 0. 9 her seg by users: wchg frequency: f W 50kHz Forward volage of secondary dode: d 0.4 Forward volage of auxlary dode: da 1.1 CC volage: CC 14 Core_ye: EE0 (e31mm ), Bmax<3000G dc_ke 50 (wh snubber crcu) Desgn es: 1) Calculae he maxmum urn rao of XFM dc_m 40, ac_m We choose 10 ) Calculae he eak curren of rmary sde and curren sense ressor ( K & C ) s k 0.97 η η We choose C C K cs 0.56Ω, 0.97, _ ref ) Calculae he ducance of rmary sde--- (51) (5) (53) (54) BCD emconducor Manufacurg med 7

8 lcaon oe 1074 η 0. 89mH (55) f η K W We choose 0.9mH. 4) Calculae he urns of rmary, secondary and auxlary sdes (,, ) K K 9.9 e B e B max (56) 100 s 10 (57) ( d ) 0.4 D 0.48 (59) dc 6) elec dodes of secondary and auxlary sdes dc_max dr (60) dc_m ax 65 (61) dc_m ax (6) dr 50 1 (58) dc_m ax da r 60 (63) 5) Check he maxmum duy cycle of rmary sde The maxmum duy cycle of rmary sde s calculaed as followg, 7) elec rmary sde MFET dc_ske dc_max (64) ds_mos 550 Desgn esuls ummary: 1.Calculae he maxmum eak curren of rmary sde and C K 970 m eak curren of rmary sde C 0.56 Ω Curren sensed ressor.desgn ransformer 0.9 mh nducance of rmary sde 10 Turn rao of rmary and secondary 100 T Turns of rmary sde 10 T Turns of secondary sde 1 T Turns of auxlary sde D MX 0.48 Maxmum duy cycle of rmary sde a DC elec dode and rmary ranssor dr 50 Maxmum reverse volage of secondary dode dar 60 Maxmum reverse volage of auxlary dode dcmax 550 olage sress of rmary ranssor BCD emconducor Manufacurg med 8

9 lcaon oe Feedback essors Desgn Fgure 6. Feedback essors Crcu From above Fgure 6, o FB ( FB1 FB FB ) D (65) 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 3771 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 BCD emconducor Manufacurg med 9

10 lcaon oe 1074 W FB FF Fgure 8. Waveform of FB The negave volage of FB ( Fgure 8) s lear o le volage. The 3771 samles o realze he le comensaon. FB FB1 FB a dc (66) 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 (67) o, E can be adjused o acheve excellen le regulaon of ouu curren. 3. ummary n order o ge good erformance of 3771, 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. BCD emconducor Manufacurg med 10