A Negative Single-Input/Multi-Output LED Driver and Its Analysis Method

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1 International Journal of Electrical Energy, Vol. 3, No. 3, September 5 A Negative Sgle-Input/Multi-Output ED Driver and Its Analysis Method Kei Eguchi and Kanji Abe Department of Information Electronics, Fukuoka Institute of echnology, 3-3- Wajiro-higashi, Higashi-ku, Fukuoka, Japan eguti@fit.ac.jp, mam5@bene.fit.ac.jp Sawai Pongswatd Department of Instrumentation and Control Engeerg, Kg Mongkut s Institute of echnology adkrabang, adkrabang, Bangkok, 5 hailand klsawai@kmitl.ac.th Shya erada and Ichirou Oota Department of Information, Communication and Electronic Engeerg, National Institute of echnology, Kumamoto College, 659- Suya, Koushi, Kumamoto, 86- Japan {terada, oota-i}@kumamoto-nct.ac.jp Abstract A negative sgle-put/multi-output (SIMO) ED driver is proposed this paper. Unlike the conventional ED driver usg SIMO boost converters, the proposed ED driver usg an SIMO buck-boost converter offers a negative stepped-down voltage to drive ED s cathodes. By turng on output switches rotation durg a transferrg process, the proposed driver can suppress the imbalance among output currents. his paper also presents a novel analysis method to estimate properties of the SIMO ED driver usg a buck-boost converter. By assumg a five-termal equivalent circuit, the proposed analysis method can derive the power efficiency and output voltages without complex matrix calculations. he theoretical analysis and experiments show the effectiveness of the proposed SIMO ED driver. component is required. However, when the EDs are mismatched, the charge-pump must switch to step-up mode due to the bad forward voltage of only one ED. o overcome this problem, Kim suggested the SISO ED driver usg a negative charge-pump [3]. By employg the dividual mode switchg, the negative charge-pump achieves high power efficiency. However, it is difficult to improve power efficiency further, because the conversion ratio of capacitor-based converters is predetermed by circuit structure. For this reason, energy loss caused by lear current regulation is considerably large. On the other hand, an SISO boost converter has been widely used [4], [5] the ductor-based ED driver. Unlike the capacitor-based ED drivers []-[3], the output voltage of the ductor-based ED driver can be adjusted by controllg the duty cycle of clock pulses. herefore, the ductor-based ED driver achieves higher efficiency than capacitor-based ED drivers. Followg this study, the ED drivers usg an SISO buck-boost converter have been proposed [6]-[9] to regulate the ED currents supplied with a wide-range put voltage source. As the case of the negative charge-pump, the ED driver usg a buck-boost converter drives the ED s cathodes. However, the circuit size of the ductor-based ED driver is larger than that of the capacitor-based ED driver, because the ductor-based ED driver requires magnetic components. For this reason, order to reduce the number of magnetic components, a sgle-put/multiple-output (SIDO) switchg converter []-[] has been proposed recent years. Fig. illustrates the block diagram of the ED driver usg a positive SIMO converter. In the conventional driver shown Fig., a positive steppedup voltage is provided to drive the EDs anodes. For example, He et al. suggested the SIMO ED driver usg a flyback converter []. However, the conventional Index erms DC-DC converters, buck-boost converters, switchg converters, negative outputs, white EDs, backlightg applications I. INODUCION As one of the most ideal backlight solutions, a lightemittg diodes (EDs) backlightg has been used electronic appliances. o drive EDs, several types of switchg converter topologies have been proposed [][]. hese converter topologies can be divided to two types: capacitor-based converter topology and ductorbased converter topology. In the capacitor-based ED driver, a sgleput/sgle-output (SISO) charge-pump has been commonly used [], [], where a positive stepped-up voltage is generated to drive the ED s anodes. he charge-pump can realize no flux of magnetic duction, small volume, and light-weight, because no magnetic Manuscript received May 8, 5; revised August 6, 5. 5 International Journal of Electrical Energy doi:.878/ijoee

International Journal of Electrical Energy, Vol. 3, No. 3, September 5 as follows. When the transistor switch S turns on, the ductor is charged by the put voltage V.

Unlike the conventional control method described [], the switches S, S,, SN of the proposed driver are turned on rotation by N-phase clock pulses. (See Fig.

3, State- is the chargg process of the ductor and States- and are the transferrg process.

) herefore, the output voltages are expressed as if the duty cycle D is set to / and the proposed driver operates a contuous conduction mode (CCM).

2 International Journal of Electrical Energy, Vol. 3, No. 3, September 5 as follows. When the transistor switch S turns on, the ductor is charged by the put voltage V. Next, the output switches S, S,, SN are turned on rotation. In State- - N, the ED s cathodes are driven by a negative stepped-down voltage, where the turn-on sequence of S, S,, SN is permutated. Unlike the conventional control method described [], the switches S, S,, SN of the proposed driver are turned on rotation by N-phase clock pulses. (See Fig..) o help readers understandg, let us discuss the simplest example of the proposed driver shown Fig. 3. In Fig. 3, State- is the chargg process of the ductor and States- and are the transferrg process. In the transferrg process, the turn-on sequence of S and S is permutated to suppress the imbalance among ED currents. (See Fig. 3.) herefore, the output voltages are expressed as if the duty cycle D is set to / and the proposed driver operates a contuous conduction mode (CCM). D V Vout Vout V D driver reported [] is bulky, because the driver reported [] requires a transformer. As distct from the ED driver usg a transformer, Hong et al. proposed the SIMO ED driver usg a boost converter []. By usg a non-isolated converter, the conventional driver reported [] can achieve smaller size than the driver reported []. However, as described [], the power efficiency of the ED driver reported [] decreases significantly due to a lear current regulation element for each channel. o overcome this problem, Kim et al. suggested the SIMO ED driver usg a boost converter with a time-division multiplexg conduction scheme. By turng on output switches by N+ (=, 3, )-phase clock pulses, the ED driver reported [] can elimate lear current regulation elements. Figure. Block diagram of the ED driver usg a positive SIMO converter. In this paper, we propose a negative SIMO ED driver. Unlike the conventional SIMO ED drivers, the proposed ED driver employs a buck-boost converter to drive ED s cathodes, because the ED driver usg an SISO buck-boost converter can achieve not only a wider put range but also better performance than the ED driver usg a SISO boost converter as described [9]. Furthermore, by turng on output switches rotation durg a transferrg process, the proposed driver can suppress the imbalance among output currents. his paper also presents a novel analysis method to estimate properties of the SIMO ED driver usg a buck-boost converter. In the traditional theoretical analysis of a switchg DC-DC converter with magnetic elements, the state-space averagg method has been commonly used [3]-[5]. However, the state-space averagg method requires complex matrix calculations. By assumg a five-termal equivalent circuit, the proposed method derives the power efficiency and output voltages without complex matrix calculations. o confirm the validity of the proposed converter, theoretical analysis and experiments are performed. he rest of this paper is organized as follows. In Section, the circuit configuration of the proposed driver is presented. In Section 3, the property of the proposed driver is analyzed by the proposed analysis method. Experimental results are shown Section 4. Fally, conclusion and future work are drawn Section 5. II. Figure. Proposed ED driver usg a sgle-put multiple-output buck-boost converter. CICUI CONFIGUAION Fig. illustrates the circuit configuration of the proposed SIMO ED driver with N (=, 3, 4, ) outputs. Unlike the conventional SIMO ED drivers [9]-[], a buck-boost converter is employed the proposed SIMO ED driver. he basic operation of the proposed driver is 5 International Journal of Electrical Energy Figure 3. Proposed ED driver with two outputs. he detailed theoretical analysis concerng the proposed driver will be described the followg section. 8

3 International Journal of Electrical Energy, Vol. 3, No. 3, September 5 III. HEOEICA ANAYSIS A. Proposed ED Driver o analyze steady-state behavior of the proposed driver, theoretical analysis is performed concerng the proposed driver with two outputs. By assumg a fivetermal equivalent circuit illustrated Fig. 4, the proposed analysis is performed, because it is known that the general equivalent circuit of the sgle-put sgleoutput SC DC-DC converter can be expressed by a fourtermal circuit [6], [7]. In Fig. 4, m is the ratio of an ideal transformer, ac is the resistance to express the ripple loss of a reactor, o, o, and o are output resistances, and are output loads. Unlike the statespace averagg method [3]-[5], the proposed analysis method derives these parameters from stantaneous equivalent circuits without complex matrix calculations. o save space, the theoretical analysis will be discussed concerng the proposed driver operatg CCM. Figure 6. Inductor current. Fig. 5 illustrates the stantaneous equivalent circuits of the proposed driver with two outputs, where on is the on-resistance of the transistor switch, d is the onresistance of the diode switch, l is the resistance of the ductor, is the ideal ductor, and Vth is the threshold voltage of the diode switch. When the proposed driver operates CCM, the current through the ductor is expressed as shown Fig. 6. In Fig. 6, the ductor currents State-, and are expressed as: i i t I D i i i, t t I D i, t () () D i t I i D i, t (3) D (4) D (5) Figure 4. Proposed five-termal equivalent model. i (6) i In ()-(3), Δi is the variation of the ductor current (see Fig. 6). Usg () - (3), the variation of the ductor current State- is given by: i i, i, V V dt (7) On the other hand, the variation of the ductor current State- and is given by: i i, i, V V dt (8) where V denotes the voltage of the ductor. From (7) and (8), we have the followg relations: (c) D V and I D I D D V Figure 5. Instantaneous equivalent circuits of the proposed driver: State-, State-, and (c) State-. 5 International Journal of Electrical Energy 8 (9)

4 International Journal of Electrical Energy, Vol. 3, No. 3, September 5 where I is the average ductor current and I is the average put current. From (9), the parameter m Fig. 4 is obtaed as: D m () D Next, order to derive the output resistances o, o, and o, the consumed energy one period is discussed. From Fig. 5, the consumed energy W can be expressed as: W i i W () (), on l () W i t dt (), l d on (3) W i t dt (), (4) l d on W i t dt herefore, usg ()-(6), (), (3), and (4), the total consumed energy one period is obtaed as: W m D I on l d out m D I on l d out m D I I on l d out out D i (5) on l d From Fig. 4, the consumed energy of the five-termal equivalent model can be defed as: W : I ac o I I o out o out o o I out o o I out m i o Iout Iout ac D Z (6) Z o o ac (7) o o herefore, from (5) and (6), we have the resistances o, o, o, and ac as follows: ac o (8) o o D on l D D ' D D Z D on l Z d d (9) () ' ac () Usg (), (8), (9), (), and (), the equivalent circuit of the proposed driver can be expressed by Fig. 7. he value of o Fig. 7 completely is equal to the value o derived by usg the state-space averagg method. In the CCM, ac becomes much smaller than o. Figure 7. Equivalent circuit of the proposed driver. From Fig. 7, the power efficiency and the output voltage of the proposed driver can be derived as: Vout Vout mv () o Iout Iout I I I (3) ac o out Equations () and (3) can be rewritten as: V out Vout o ac o m V out (4) (5) If the output loads satisfy = =. As ()-(5) show, the proposed analysis method can estimate the characteristics without complex matrix calculations. Figure 8. Conventional driver with two outputs. Figure 9. Five-termal equivalent model for the conventional driver with two outputs. 5 International Journal of Electrical Energy 8

5 International Journal of Electrical Energy, Vol. 3, No. 3, September 5 As the same way, the total consumed energy of the conventional driver is expressed as (5). On the other hand, the consumed energy of Fig. 9 can be defed as: W : o o I out o o I out o I out I out ac Z ac m i D Z o o o o (3) (3) herefore, from (5) and (3), we have the resistances o, o, o, and ac as follows: (3) o o o on l D d D (c) Figure. Instantaneous equivalent circuits of the conventional driver: State-, State-, and (c) State-. B. Conventional ED Driver Fig. 8 illustrates the conventional ED driver usg a boost converter with two outputs. he steady-state behavior of the conventional driver is analyzed by assumg a five-termal equivalent circuit shown Fig. 9. he stantaneous equivalent circuits of the conventional driver are expressed as Fig., where the proposed control method is used to compare the characteristics of the conventional driver with that of the proposed driver. In Fig., the current through the ductor is also expressed as shown Fig. 6. herefore, the ductor currents State-, and are expressed as (), (), and (3), respectively. In Fig. 8, the variation of the ductor current State- is given by: i i, i, V dt V (6) On the other hand, the variation of the ductor current State- and is given by: i i, i, V V dt ac D D Z ' on Z ' ac V and I D I D IV. EXPEIMEN In the experiments, we focused on the verification of the circuit topology. herefore, the experimental circuit was built with commercially available ICs on a bread board. Concretely, the experimental circuit of the proposed converter with two outputs was built with photo-mos relay AQV, Darlgton sk driver D64 APG, microcontroller PICF8, and diode N47 on a bread board, where V = 3V, Cout = Cout = μf, =mh, =6Hz and ==3kΩ. Fig. shows the measured clock pulses, where Fig. describes the traditional control method and Fig. describes the proposed control method. As Fig. shows, the switches S and S is turned on rotation. (8) herefore, the parameter m Fig. 9 is obtaed as: m (9) D 5 International Journal of Electrical Energy 83 (35) As (9) and (33) show, the output resistance of the proposed driver, o, is smaller than that of the conventional driver, because <D<. herefore, from (3) and (5), the proposed driver can achieve higher efficiency than the conventional driver. V V V l D d (34) (7) From (6) and (7), we have the followg relations: (33)

International Journal of Electrical Energy, Vol. 3, No. 3, September 5 efficiency of the proposed SIMO ED driver were obtaed without complex matrix calculations.

Furthermore, theoretical results demonstrated that the proposed driver can achieve higher efficiency than the conventional driver; and ) By turng on output switches rotation, the imbalance among

he detailed experiment of the proposed converter is left to a future study. Figure. Measured clock pulses: traditional control method and proposed control method.

6 International Journal of Electrical Energy, Vol. 3, No. 3, September 5 efficiency of the proposed SIMO ED driver were obtaed without complex matrix calculations. he derived theoretical formulas will be helpful to estimate the characteristics of the proposed SIMO ED driver. Furthermore, theoretical results demonstrated that the proposed driver can achieve higher efficiency than the conventional driver; and ) By turng on output switches rotation, the imbalance among output currents was suppressed. In the proposed driver with two outputs, the current balance error of the proposed converter was.47%. he detailed experiment of the proposed converter is left to a future study. Figure. Measured clock pulses: traditional control method and proposed control method. EFEENCES [] [] [3] [4] [5] [6] [7] [8] Figure. Measured output voltages: traditional control method and proposed control method. [9] Fig. shows the measured output voltages. In the traditional control method of Fig., the output voltages Vout and Vout are -.7V and -.V, respectively. On the other hand, the proposed control method, the output voltages Vout and Vout are -.77V and -.8V, respectively. As Fig. shows, the proposed driver can reduce the current balance error. Concretely, the conventional driver, the difference between the output currents Iout and Iout is.4ma. On the other hand, the proposed driver, the difference between the output currents Iout and Iout is 5.μA. In this case, the current balance error of the proposed driver is.47%. V. [] [] [] [3] CONCUSION A sgle-put/multi-output (SIMO) ED driver and its analysis method have been proposed this paper. he results of this study are as follows: ) By assumg a fivetermal equivalent circuit, the output voltages and power 5 International Journal of Electrical Energy [4] 84. Guo, Z. iang, and A. Q. Huang, A high efficiency transformerless step-up DC-DC converter with high voltage ga for ED backlightg applications, Proc. wenty-sixth Annual IEEE Applied Power Electronics Conference and Exposition,, pp. 6-. Y. M. Wang, W.. Deng, X. Y. Ma, W. Y. Huang, and J. K. Huang, Design of a white ED backlight driver IC based on a new three-mode charge pump, Proc. IE Int. Conf. on Information Science and Control Engeerg,, pp. -4. J. Kim, Negative charge pumps achieve ductor-like efficiency for WED backlights, MAXIM Engeerg Journal, vol. 64, pp. 3-5, Jan. 9. Y.. Hsieh, B. D. iu, J. F. Wu, C.. Fang, H. H. sai, and Y. Z. Juang, A high efficiency boost white ED driver for portable electronics applications, Proc. International Symposium on Next-Generation Electronics,, pp , S. Y. iu, and H. W. Chiang, Optimal ED array combation for sgle-loop CCM boost driver, Proc. IEEE Industry Applications Conference,, pp. -7. K. Eguchi, S. Pongswatd,. Watanabe, P. Pannil, K. irasesth, and H. Sasaki, A white ED driver usg a buck-boost converter, IEEJ ransactions on Electrical and Electronic Engeerg, vol. 5, no. 5, pp , Aug.. K. Eguchi, S. Pongswatd, A. Julsereewong, I. Oota, S. erada, and H. Sasaki, Design of a dual-put buck-boost converter for mobile back-lightg applications, International Journal of Innovative Computg, Information and Control, vol. 8, no. 4, pp. 9-94, Apr...., Y. C. Chang, and C. C. ee, Optimal design of ED array for sgle-loop CCM buck-boost ED driver, IEEE rans. on Industry Applications, vol. 49, no., pp , Mar./Apr. 3..., J. Y. sai, S. Y. iu, and H. W. Chiang, Optimal design of ED array combations for CCM sgle-loop control ED drivers, IEEE Journal of Emergg and Selected opics Power Electronics, vol. 3, no. 3, pp , Mar. 5. Y. He, J. Xu, and S. Zhong, HB-ED driver based on sgleductor-dual-output switchg converters pseudo-contuous conduction mode, Proc. International Conference on Communications, Circuits and Systems, 3, pp S. I. Hong, J. W. Han, D. H. Kim, and O. K. Kwon, A doubleloop control ED backlight driver IC for medium-sized CDs, Proc. IEEE International Solid-State Circuits Conference Digest of echnical Papers,, pp H. C. Kim, C. S. Yoon, D. K. Jeong, and J. Kim, A sgleductor, multiple-channel current-balancg ED driver for display backlight applications, Proc. IEEE Energy Conversion Congress and Exposition, 3, pp A. Emadi and A. Abur, eal time state estimation of multiconverter DC power electronic systems usg generalized state space averagg method, Proc. IEEE 33rd Annual Power Electronics Specialists Conference,, pp M. M. Jalla, A. Emadi, G. A. Williamson, and B. Fahimi, eal time state estimation of multi-converter more electric ship power systems usg the generalized state space averagg method, Proc. 3th Annual Conference of IEEE Industrial Electronics Society, 4, pp

International Journal of Electrical Energy, Vol. 3, No. 3, September 5 [5] S. Yang, K. Goto, Y. Imamura, and M.

5-7, Jan.. [7] K. Eguchi, I. Oota, S. Pongswatd, A. Julsereewong, K. irasesth, and H.

4, pp. 675-688, Apr.. Kei Eguchi was born Saga, Japan 97. He received the B.Eng., the M.Eng., and the D.Eng. degree from Kumamoto University, Kumamoto, Japan 994, 996, and 999, respectively.

From 999 to 6, he was an Associate Professor and a ecturer Kumamoto National College of echnology. From 6 to, he was an Associate Professor Shizuoka University.

7 International Journal of Electrical Energy, Vol. 3, No. 3, September 5 [5] S. Yang, K. Goto, Y. Imamura, and M. Shoyama, Dynamic characteristics model of bi-directional DC-DC converter usg state-space averagg method, Proc. IEEE 34th International elecommunications Energy Conference,, pp. -5. [6] K. Eguchi, S. Pongswatd, K. irasesth, H. Sasaki, and. Inoue, Optimal design of a sgle-put parallel DC-DC converter designed by switched capacitor techniques, International Journal of Innovative Computg, Information and Control, vol. 6, no. (A), pp. 5-7, Jan.. [7] K. Eguchi, I. Oota, S. Pongswatd, A. Julsereewong, K. irasesth, and H. Sasaki, Synthesis and analysis of a dual-put parallel DC-DC converter designed by usg switched capacitor techniques, International Journal of Innovative Computg, Information and Control, vol. 7, no. 4, pp , Apr.. Kei Eguchi was born Saga, Japan 97. He received the B.Eng., the M.Eng., and the D.Eng. degree from Kumamoto University, Kumamoto, Japan 994, 996, and 999, respectively. His research terests clude nonlear dynamical systems, telligent circuits and systems, and low-voltage analog tegrated circuits. From 999 to 6, he was an Associate Professor and a ecturer Kumamoto National College of echnology. From 6 to, he was an Associate Professor Shizuoka University. In, he joed the faculty of Fukuoka Institute of echnology, where he is now a Professor. Prof. Dr. Eguchi received ICIAE5 Best Presentation Award, ICPEE4 Excellent Oral Presentation Award, icabse4 Excellent Paper Award, KKU-IENC4 Outstandg Paper Award, ICEEN4 Excellent Paper Award, J-AEME3 Best Paper Award, ICEEP3 Best Session Paper Award, akayanagi esearch Encourage Award, Paper Award of Japan Society of echnology Education, ICICIC9 Best Paper Award, and ICINIS9 Outstandg Contribution Award. He is a senior member of IEEJ and a member of IEICE, INASS, and JSE. Kanji Abe was born Fukuoka, Japan 993. He received the B.Eng. degree from Fukuoka Institute of echnology, Fukuoka, Japan 4. His research terests switchedcapacitor power supply. From 4, he has been with Graduate School of Engeerg, Fukuoka Institute of echnology, where he is now a first year master s student. Mr. Abe received ICIAE5 Best Presentation Award. Sawai Pongswatd was born Bangkok, hailand 97. He received the B.Eng., the M.Eng., and the D.Eng. degree from Kg Mongkut s Institute of echnology adkrabang, Bangkok, hailand 994, 997, and, respectively. His research terests clude programmable logic control, energy conversion, factory automation, and fieldbus technology. From 995, he has been with Kg Mongkut s Institute of echnology adkrabang, where he is now an Associate Professor. Dr. Sawai received ICICIC9 Best Paper Award. Shya erada was born Yamaguchi, Japan 979. He received the B.Eng., the M.Eng., and the D.Eng. degree from Sojo University, Kumamoto, Japan, 5, and 7, respectively. His research terests switched-capacitor power supply. From 7, he has been with Kumamoto National College of echnology, where he is now an Associate Professor. Dr. erada received Student Paper Award IEEE MWSCAS 4. He is a member of IEICE and IEEE. Ichirou Oota was born Miyazaki, Japan 955. He received the B.Eng., the M.Eng., and the D.Eng. degree from Kumamoto University, Kumamoto, Japan 979, 98, and 99, respectively. His research terests clude switched capacitor circuits, switchg converters, and computer simulation for switchg circuits. From 98, he has been with Kumamoto National College of echnology, where he is now a Professor. From 994 to 995, he was an oversea researcher University of California, Berkeley. Prof. Dr. Oota is a member of IEICE and IEEJ. 5 International Journal of Electrical Energy 85

A FIBONACCI-TYPE DC-AC INVERTER DESIGNED BY SWITCHED CAPACITOR TECHNIQUE. Received January 2016; revised May 2016

A FIBONACCI-TYPE DC-AC INVERTER DESIGNED BY SWITCHED CAPACITOR TECHNIQUE. Received January 2016; revised May 2016 International Journal of Innovative Computing, Information and Control ICIC International c 06 ISSN 349-498 Volume, Number 4, August 06 pp. 97 07 A FIBONACCI-YPE DC-AC INVERER DESIGNED BY SWICHED CAPACIOR