Power Efficient Battery Charger by Using Constant Current/Constant Voltage Controller

Transcription

1 Circuis and Sysems, 01, 3, hp://dx.doi.org/10.436/cs Published Online April 01 (hp:// Power Efficien Baery Charger by Using Consan Curren/Consan olage Conroller Falah Al Hassan Deparmen of Elecrical and Elecronics Engineering, Easern Medierranean Universiy, Famagusa, Norh Cyprus Received March 4, 01; revised April 3, 01; acceped April 10, 01 ABSTRACT The Baery Charger Specificaion presens soluion for rechargeable baeries used in porable elecronic equipmen such as lapop compuer sysems, cellular elephones and video cameras and he demands for low cos baery chargers are rising hese days wihou give aenion for he performance. The goal of he paper was combining high efficiency and versailiy wih low-cos design and his paper includes he design of he snubber cell, and he componens of he curren/volage conrol charge mehod. This charger applies a relaively consan curren and consan volage o he baery indefiniely regardless of he AC inpu rang volage all he equaions described in his paper. The design of prooype converer is verified hrough an experimenal resul. Keywords: Baery Charger; Flyback; Consan Curran; Consan olage; Snubber; Efficiency 1. nroducion The main funcion of any baery charger is o cause curren o flow back ino a baery in he opposie direcion from which curren flowed during discharge. A baery on charge is no a fixed or saic load. has a volage of is own and is conneced o he charger so ha he wo volages oppose each oher. Thus, he curren ha flows is he resul of he difference beween he volages of he charger and he baery and a funcion of he low ohmic resisance of he baery. The volage of he baery iself rises during he charge, furher opposing he flow of curren as he charge progresses. The basic requiremens of a charger as hey relae o he baery are a safe value of charging curren hroughou he enire cycle, proecion agains condiions ha would resul in overcharge, and accurae erminaion of he charge when complee or reducion of he curren o a level which provides a safe charge mainenance value. The desired characerisics of a charger as hey relae o he user are Maximum reliabiliy, Auomaic operaion o he degree pracical in he applicaion, Simpliciy in design and consrucion, Good efficiency and power facor, Ease of operaion, Reasonable cos and rapid charging. Baery chargers are designed ypically around wo modes of operaion, namely, consan-volage charging and consan-curren charging. The former uilizes a consan volage source and an equivalen series resisance o conrol he amoun of curren ha flows ino he baery. As soon as he baery volage is raised o he volage sources, he converer mus limi is curren o preven excessive dissipaion. The laer, moreover, keeps he charging curren consan unil he baery volage reaches a designaed value [1]. Tiny swich reduces oal componen coun, design size, weigh and, a he same ime increases efficiency when compared o MOSFET or RCC swich, Figure 1 shows he schemaic of he basic baery charger, which also serves as he reference circui for he design proposes.. Proposed Baery Charger Topology A charger drive circui ha consiss of a flyback DC-DC converer wih a snubber cell and a consan oupu curren and volage conrol as a driver for baery charger is proposed. Wih his drive circui, he charger sysem becomes small size, and has a higher efficiency especially. The configuraion for he circui o charge baery by consan curren and consan poenial mehod is shown in Figure 1, where N P and N S winding is a high-frequency ransformer, C DC is he inpu filer capacior, C P is he oupu filer capacior, DC is he DC inpu volage generaed by recifying AC volage using a bridge recifier diode, o is he oupu volage, o is he oupu curren, D R is a recifier diode and U1 is a power managemen C wih a MOSFET incorporaed in i conneced o a phooelecrical coupler used for phoo-elecronic isolaion. The proposed consan oupu curren and volage circui is based on negaive-feedback-conrol heory. Copyrigh 01 SciRes.

2 F. AL HASSAN 181 Figure 1. The basic baery charger circui. High-frequency ransformer is used o ransfer energy from inpu-end o oupu-end. During he ON period for he inegraed MOSFET, ransformer sores energy in is primary winding and he oupu curren is supplied from he oupu filer capaciy C P only. When he MOS- FET Turns OFF, he energy sored in he power ransformer is ransferred o he baery load and o C P as i replaces he charge i los when i was alone delivering load curren. Curren conroller and volage conroller generaes a conrol signals by comparing he deeced volage wih a predeermined reference volage. U1 regulaes he ON/OFF ime of he inegraed MOSFET according o he corresponding conrol signals, providing a consan oupu curren and consan oupu volage wih high efficiency convering o he baery a las..1. Power Managemen C A piece of power managemen C-TNY77, a member of TinySwich- family produced by Power negraions nc., is used in he drive circui. TNY77 incorporaes a high-volage power MOSFET wih a power supply conroller in one device, using an ON/OFF conrol scheme and offers a design flexible soluion wih a low sysem cos and exended power capabiliy. The pin configureion of TNY77 is shown in Figure 1, where D pin is he power MOSFET drain connecion, providing inernal operaing curren for boh sar-up and seady-sae operaion and S pin is inernally conneced o he oupu MOSFET source for high volage power reurn and conrol circui common. EN/U pin has dual funcions: enable inpu and line under-volage sense. During normal operaion, swiching of he power MOSFET is conrolled by his pin []... RCD Snubber Cell Selecion When he power MOSFET is urned off, here is a high volage spike on he drain due o he ransformer leakage inducance. This excessive volage on he MOSFET may lead o an avalanche breakdown and evenually failure of he Tiny swich. Therefore, i is necessary o use an addiional nework o clamp he volage. The RCD snubber circui and MOSFET drain volage waveform are shown in Figures and 3, respecively. The RCD snubber nework absorbs he curren in he leakage inducance by urning on he snubber diode D sn once he MOSFET drain volage exceeds he volage of node X as depiced in Figure. n he analysis of snubber nework, i is assumed ha he snubber capacior is large enough ha is volage does no change significanly during one swiching cycle. The snubber capacior used should be ceramic or a ma- erial ha offers low ESR. Elecrolyic or analum capa- ciors are unaccepable due o hese reasons [3-5]. The firs sep in designing he snubber circui is o deermine he snubber capacior volage a he minimum inpu volage and full load condiion ( sn ). Once sn is deermined, he power dissipaed in he snubber nework a he minimum inpu volage and full load condiion is obained as ds 1 sn s lk ds Peak Rsn P f L sn where ds peak is he maximum peak curren hrough he TNY77 a he minimum inpu volage condiion, f s is he TNY77 swiching frequency, L lk is he leakage in-ducance, sn is he snubber capacior volage a he minimum inpu volage and full load condiion, R is he refleced oupu volage and R sn is he snubber resisor. sn Should be larger han R and i is ypical o se sn o be.5 imes R. Too small a sn resuls in a severe loss in he snubber nework as shown in Equaion (1). The leakage inducance is measured a he swiching frequency on he primary winding wih all oher windings shored. Then, he snubber resisor wih proper raed waage should be chosen based on he power loss. The maximum ripple of he snubber capacior volage is ob- sn R (1) Copyrigh 01 SciRes.

3 18 F. AL HASSAN ained as sn ds Peak sn DC min Figure 3. volage. Figure. RCD snubber circui. ds Peak ds Peak sn R sn ds Peak Minimum inpu volage Maximum inpu volage and Full load and Full load MOSFET drain volage and snubber capacior R sn sn () CsnRsn fs where f s is he TNY77 swiching frequency. The snubber capacior volage ( sn ) of Equaion (7) is for he minimum inpu volage and full load condiion, When he converer is designed o operae in CCM under his condiion, he peak drain curren ogeher wih he snubber capacior volage decrease as he inpu volage increases as shown in Figure 3. The peak drain curren a he maximum inpu volage and full load condiion ( ds Peak ) is obained as Pin ds Peak (3) f L where he maximum i npu power P in, is given by P in P o s P (4) where Po is he oupu power and he η is he circui efficiency. And he ransformer primary side inducance L P is given by DC min Dmax LP (5) P f k in s where k is he is he ripple facor in full load and minimum inpu volage condiion and DC min is he minimum DC link volage and he maximum duy cycle raio D max is given by R Dmax (6) DC min he snubber capacior volage under maximum inpu volage and full load condiion is obained as sn R f L R R sn s lk ds Peak where f s is he TNY77 swich frequency, L lk is he primary side leakage inducance, R is he refleced oupu volage and R sn is he snubber resisor. From Equaion (7), he maximum volage sress on he inernal MOSFET is given by ds max sn R (7) (8) where is maximum DC link volage given by line max (9) in his secion he snubber cell elemens seleced successfully o improve he efficiency and performance of he proposed charger..3. Analysis for he Consan-Oupu-Curren and Consan-Oupu olage Circui n general, a baery charger employs consan curren (CC)/consan volage (C) conrol circui for an opimal charge of a baery. Figure 4 shown a consan curren (CC)/consan volage (C) circui based on he flyback converer is proposed in his paper, a simple, low cos circui using a comparaor (U3) and shun regulaor (U4), being validaed wih a parameric deailed analysis provided in his secion. DC inpu volage DC is generaed by recifying AC inpu volage AC using a bridge recifier, and is maximum is specified in Equaion (9). Assume ha he swiching frequency and he ON period for he power MOSFET are f s and on, respecively. Then duy raio D is defined according o he following equaion: D f (10) s The inpu power P i for he drive circui is calculaed by Equaion (4) where P o is he oupu power and he η is he circui efficiency. Thus he average primary curren i on Copyrigh 01 SciRes.

4 F. AL HASSAN 183 is represened as follows: Figure 4. CC/C conrol circui for baery charger. Pi Po i (11) Assume ha he iniial curren in primary winding is zero ampere. During he MOSFET ON period, here is a fixed volage across primary winding and curren in i ramps up linearly. A he end of he ON period, he primary curren has ramped up o p, as shown in Figure 5(a). The relaionship beween i and p can be represened as follows: i p (1) f The power oupu of he flyback circui is deermined by he primary inducance L P and he primary curren p, where L P can be calculaed as on L (13) P When MOSFET urns OFF, he curren in he magneizing inducance forces a reversal of polariies on primary winding. Since he curren in an inducor canno change insananeously, a he insan of urn OFF, he primary curren ransfers o he secondary a an ampliude N p s p (14) N where N p, N s, are he primary and secondary winding urns. During he MOSFET OFF period, he secondary curren ramps down linearly, shown in Figure 5(b), wih an average value calculaed as on p s 1 f on av (15) Finally, from (10)-(14) and by using Equaion (4), he s circui oupu volage o can be represened as he following equaion: on o (16) N 1 f on where N is he primary/secondary urns raio. Assume ha he reference volage in Figure 4 is ref, he volage deeced by R d is d and he volage across he zener diode U4 is z, hen he r and d is given by follwing equaions: R r z R3 R (17) d o Rd (18) when d > r he phooelecrical coupler (U) and he MOSFET urns OFF o reduce he oupu curren. On he conrary, if d < r, he phooelecrical coupler leaves off work and he MOSFET urns ON, helping increasing he oupu curren. Consan volage (C) conrol: The volage divider nework of R 4 and R 5 should be designed o provide z o he reference pin of he U4. The relaionship beween R 4 and R 5 is given by Z R4 R5 (19) O Z f where o is he oupu volage. By Assuming R 4 i is easily o obained R 5. The feedback capacior (C F ) inroduces an inegraor for C conrol. To guaranee sable operaion, C F of 470 nf is chosen. R 1 should be designed o provide proper operaing curren for he shun regulaor (U4) and o guaranee he full swing of he feedback volage for he TNY 77 Swich. Finally a snubber cell and consan oupu curren and consan oupu volage elemens are obained hus he final scheme of he proposed fly back converer is shown in Figure 6. S on T P (a) av i off T (b) Figure 5. Curren waveform in primary winding (a) and (b) Copyrigh 01 SciRes.

5 184 F. AL HASSAN secondary winding. Figure 6. The final scheme of he proposed fly back converer. 3. Experimenal Resul of Proposed Charger n order o show he validiy of he proposed baery charger presened in his paper, he fly back converer wih snubber cell and consan curren/consan volage conroller has been buil and fabricaed wih an inpu range of AC volage and he oupu of 5 /1 A wih 94% efficiency. All he circui elemens values and par number based on Figure 6 are given in Table 1 in Appendix. Under a consan inpu of 85 AC he oupu volage vs he oupu curran is shown in Figure 7 and Figure 8 shows he TNY77 drain volage ds and drain curren ds waveforms under a consan inpu of 85 AC. Under an inpu range of AC he circui oupu volage approximaely 5 and he oupu curren approximaely 1 A as shown in Figures 9 and 10 respecively also he proposed circui efficiency according he inpu AC volage range is clearly shown in Figure 11. driving mehod, and i s mos effecive under differen Figure 7. Oupu volage vs oupu curren. 4. Conclusion A consan oupu curren and consan oupu volage and snubber circui based on he flyback converer is invesigaed and a circui prooype wih an oupu of 5 /1 A is designed and fabricaed he experimens resuls sugges ha he proposed driving mehod has a high accuracy, good sabiliy and high efficiency. The simulaions and experimenal resuls have proven good performances and verify he feasibiliy of he proposed Copyrigh 01 SciRes.

6 F. AL HASSAN 185 Figure 8. Waveforms of drain curren and volage a 85 AC volage a full load condiion. Oupu DC volage Oupu Curran npu AC volage Figure 9. Oupu volage vs inpu AC volage. condiions of indusrial applicaions. 5. Acknowledgemens would like o express my sincere graiude o Prof. Dr. Osman Kukrer for his invaluable help and suppor all over his work. REFERENCES [1] N. K. Poon, B. M. H. Pong and C. K. Tse, A Consan-Power Baery Charger wih nheren Sof Swiching and Power Facor Correcion, EEE Transacion on Power Elecronics, ol. 18, No. 6, 003, pp doi: /tpel [] T. Liu, S. Wang, S. Song and Y. Ai, Research on High Efficiency Driving Technology for High Power LED Lighing, Asia-Pacific of Power and Energy Engineering Conference, Chengdu, 8-31 March 010, pp [3] P. C. Todd, Snubber Circuis: Theory, Design and Applicaions, Texas nsrumen, Dallas, 001. [4] S. J. Finney, B. W. Williams and T. C. Green RCD Snubber Revisied, EEE Transacion on ndusry Applicaion, ol. 3, No. 1, 1996, pp [5] S. Y. R. Hui and H. Chung, Resonan and Sof-Swiching Converers, n: M. H. Rashid, Ed., Power Elecronics Handbook, Academic Press, Cambridge, 000, pp npu AC volage Figure 10. Oupu curren vs inpu AC volage. Effiency % npu AC volage Figure 11. The proposed circui efficiency according he inpu AC volage range. Copyrigh 01 SciRes.

7 186 F. AL HASSAN Appendix The able bellow shows he elemens values and par numbers of he proposed charger. Table 1. The proposed circui elemens value and par numbers. Circui Elemens alues Par number C DC 6.8 µf Any R sn 70 KΩ Any C sn 470 ρf Any C o 330 µf Any C p 330 µf Any C F 470 µf Any C 1 nf Any L 1.8 µh Any R 1 56 Any R 1 KΩ Any R KΩ Any R 4 KΩ Any R 5 KΩ Any R d 0.56 Ω Any D sn - UF4007 D R - SB360 U1 (swich) - TNY77 swich U (phooelecrical coupler) - H11A817A U3 (comparaor) - KSP U4 (zener diode) - KA431 Transformer winding - EER1616 Bridge recifier diodes - 1N4007 Copyrigh 01 SciRes.