I J C T A, 9(16), 216, pp. 8333-8339 Internatinal Science Press DC-DC Duble PWM Cnverter fr Dimmable LED Lighting Pavankumar, Rhit Shinde and R. Gunabalan* ABSTRACT A simplebuck-bst cnverter tplgywith a dimming feature using duble PWM technique is presented fr autmtive lighting applicatins. The pwer circuit is simple and cst effective.the buck-bst cnverter hassingle cntrlled switch and fur energy string devices t perfrm bthperatins. The design f utput filter capacitr is made small t use film capacitr in rder t increase the life time f LED driver circuit. Simulatin is perfrmed in matlab-simulink fr a pwer rating f 1W LED array lad with an input vltage f 24V DCand the perfrmance f the cnverter is presented under nrmal LED lighting and dimming cnditins t prve the effectiveness f the cntrl technique. Keywrds: Autmtive lighting, buck-bst cnverter, LED lamp, PWM methd 1. INTRODUCTION The light emitting dide (LED) lamps are mre efficient and give maximum illuminatin and they replace the inefficient autmtive lighting. They are cmpact in size, mre reliable and highly efficient.fr LEDs, the electrns and hles recmbinatin prduces phtns in terms f light and causes increase in junctintemperature which degrades in luminus flux f LEDs.The peratinal lives f LED bulbs clearly distinguish them frm rdinary bulbs. LEDs are current driven devices and t maintain the current cnstant, theled driver circuits are intended t wrk in cntinuus cnductin mde[1]. Dimming f LEDs is adpted by varying the current thrugh them. The life time f dimmable bulbs can be 1, hurs. The brightness f the LED can be tuned by varying then and ff time f LED current [2]. There are different methdlgies are existing in literatures fr LED dimming. PWM dimming circuits are emplyed t avid flicker and clur shift in LED lighting with a lw frequency range f 1 Hz t 2 Hz.Digital dimming using lw frequency pulse width mdulatin t avid chrmaticity shift prblem was studied and experimentally verified fr a frequency f 2 Hz [3]. The light intensity f the LED is cmparative t its average current. A duble PWM (DPWM) lw frequency gate driver circuit was adpted t regulate the average current and its amplitude t stp the LED lighting frm clr swing [4]. Simple flyback cnverter was emplyed in discntinuus cnductin mde with high efficiency t drive a LED lad f 45 W. An integrated duble buck-bst (IDBB) cnverter LED driver circuit was presented in [5] fr street lighting applicatins. Single stage parallel cnnected cnstant vltage and cnstant current driver circuit in which linear dimming cntrl was applied fr LED streetlighting applicatins [6]. Three dimming levels were realized with reduced pwer lss and gd efficiency (>9%).Dimmable valley fill sepicled driver was develped fr lw pwer applicatins using IC 555 timer in astable mde with ne cycle cntrl [7]. PWM cntrl was usedwithin a duty cycle range f 5% t 95% t vary the brightness f the LED lamps. PWM dimming with frequencies abve the audible range fr illuminatin cntrl was designed and tested in rder t avid the audible nise. A shunt switch was cnnected acrss the LED string t vary the * Schl f Electrical Engineering VIT University Chennai, Email: gunabalanr@yah.c.in
8334 Pavankumar, Rhit Shinde and R. Gunabalan average current [8]. Dimming linearity was maintained fr a range f 2% t 8% f its maximum brightness. A lw frequency PWM cntrl was emplyed t dim the LEDs with high line input pwer factr and reduced input current ttal harmnic distrtin [9]. A buck-bst cnverter and a buck cnverter were integrated and perated in discntinuus and cntinuus cnductin mde respectively. Dimming cntrl was perfrmed by varying the duty cycle f the lw frequency signal which is used t cntrl the active switch in the buck cnverter. Nn-linear clsed lp cntrl was used in [1] fr dimming and clur cntrl f LED lamps. Average current mde cntrlled inverse buck dimmable LED driver with an integrated current cntrl technique was implemented with a pwer efficiency f 98.16% and a dimming range f 5 % t 95 % [11].In this prpsed wrk, duble PWM technique is incrprated with mdified IDBB cnverter t enable dimming featurewithut flickering and clur shift and als fr better efficiency and lw LED current ripple. 2. DOUBLE PWM TECHNIQUE WITH MODIFIED IDBB CONVERTER The blck diagram f IDBB cnverter is depicted in Figure 1. The cnverter cntains three dides, tw capacitrs, tw inductrs and ne cntrlled switch. This cnverter is cnnected t the battery f autmtive vehicle r the battery f the slar LED lighting fr greater efficiency and lw LED current ripple. In the pwer circuit diagram f mdified IDBB cnverter shwn in Figure 2, the capacitr C B and dide D 1 are interchanged as cmpared t the IDBB cnverter discussed in [5]. The input inductr L i is functined Figure 1: Blck diagram f IDBB Cnverter Figure 2: Pwer circuit diagram fr mdified IDBB cnverter
DC-DC Duble PWM Cnverter fr Dimmable LED Lighting 8335 Figure 3: Duble pulse width mdulatin cntrl signal in cntinuus cnductin mde in nrmal perating cnditin and discntinuus cnductin mde during dimming. In the same way, the utput inductance L can als be perated in cntinuus and discntinuus cnductin mde respectively during nrmal mde and dimming. The cnverter is perated with cnstant utput vltage and current t minimize the lw frequency vltage and current ripple under nrmal lighting cnditins. Duble pulse width mdulatin technique is emplyed t perate the LED lighting in dimming by mixing a high and lw frequency signals. The luminsity f the LED is apprximately prprtinal t the average current and dimming can be achieved by adjusting the duty rati f the cntrl signal. But there might be a current deviatin in LED which may cause clr swing. T prevent the clr shift, PWM fr lw frequency can be used anddpwm is used t regulate the amplitude f the pulse current and pulse average synchrnusly. Figure 3 reflects the DPWM cntrl pulse pattern. High frequency signal is cmbined with the lw frequency signal t btain discntinuus cnductin. Cnsequently the LED is driven thrugh a pulsed current. 3. DESIGN OF MODIFIED IDBB CONVERTER Theanalysis f IDBB cnverter was explained in detail [5] when perated frm the main vltage. The cnverter cmpnents are designed fr ffline autmtive lighting applicatins fr a pwer rating f 1 W and it is perated frm the battery vltage. The design analysis presented in [4] is reprduced fr easy understanding. The input and utput pwer is given by the fllwing terms fr the IDBB cnverter: The utput vltage is calculated frm the given frmula, Pin Vb I in (1) P V I (2) V DV b 2 K (3)
8336 Pavankumar, Rhit Shinde and R. Gunabalan where K is nn-dimensinal factr is given by, The input inductance is calculated by, K fsli R (4) L i D V 4P f 2 2 b The bus vltage V B is calculated when the cnverter is perated in cntinuus cnductin mde [11], V B 1 The utput capacitr (C ) and utput inductr(l )are expressed using the fllwing standard equatins [11]: D D s V (5) (6) L DV.5 I B L f s (7) C where I L and V are the high frequency peak t peak current and vltage ripple respectively. DI V f s (8) 4. SIMULATION RESULTS AND DISCUSSIONS Themdified IDBB cnverter is designed fr a pwer rating f 1 W and simulated in matlab-simulink. The Cnverter supplied by input supply vltage V dc = 24V drawn frm the battery whereas the utput vltage is V = 24Vfr a duty cycle f.423 and the utput current is I =.35A t serve 1W pwer t the lad f LED array.duty cycle f the high frequency signal is.423, and the switching frequency is 5kHz. The input inductrcurrent I Li =.8A and the utput inductr current I LO = -.8A. The desired parameters and their ratings fr mdeling the cnverter in the sftware envirnment are given in Table.1. Simulatin is dne in Simulink t illustrate the perfrmance f the cnverter and results are presented fr different perating cnditins. Figure 4 shws the simulatins wavefrms f the LED driver circuit fr a rated lad current f 35 ma. The internal resistance and vltage f the LED array is 9 Ù and 17.5 V respectively. The duty cycle f the pwer electrnic switch is limited t.423 t perate it in cntinuus cnductin mde with a switching frequency f 5 khz. The vltages acrss the capacitrs, currents thrugh the inductrs are illustrated in Figure 4. It shws that the current is cntinuus in bth the inductrs with minimum current ripples. Table 1 Parameters fr mdified IDBB cnverter Input inductance (Li) Output inductance (L) Input capacitance (C B ) Output capacitance (C) Output pwer Output current 12 H 2.8mH 41.75 F 74 F 1W 35 ma
DC-DC Duble PWM Cnverter fr Dimmable LED Lighting 8337 (a) Input capacitr vltage (b) Input inductr current (c) Output capacitr vltage (d) Output inductr current (e) LED vltage Figure 4: Simulatin results in nrmal LED lighting (f) LED current
8338 Pavankumar, Rhit Shinde and R. Gunabalan (a) Input capacitr vltage (b) Input inductr current (c) Output capacitr vltage (d) Output inductr current (e) LED vltage Figure 5: Simulatin results in dimmable LED lighting (f) LED current
DC-DC Duble PWM Cnverter fr Dimmable LED Lighting 8339 Fr dimming applicatins, the high frequency signal is mixed with the 1 Hz lw frequency signal using DPWM technique t eliminate clur shift and flicker. Figure 5 shws the wavefrms btained in dimmable LED lighting with capacitr vltages and inductr currents. The pulse width f the lw frequency signal is varied keeping cnstant pulse width f the high frequency signal. The wavefrms are btained fr half the rated LED current (178 ma) and the lad vltage is 19.55 V. Figure 5 (e) and 5 (f) shw the LED vltage and current wavefrms respectively. The cnverter is perated in discntinuus cnductin mde fr light dimming. 5. CONCLUSION The perfrmance f the mdified IDBB cnverter with dimming feature by applying DPWM was designed and simulated in matlab-simulinkenvirnment. The lw frequency PWM eliminates the flicker and clur shift. The designed mdel is verified fr 1W LED array lad. The life time f the driver circuit can be increased if film capacitrs are used instead f electrlytic capacitrs fr implementatin.it is cheap in cst fr decrative lighting, street lighting, aut-mtive lighting, traffic lighting and husehld appliances. REFERENCES [1] Q. Hu, R. Zane, LED driver circuit with series-input-cnnected cnverter cells perating in cntinuus cnductin mde, IEEE Trans. Pwer Electrn., vl. 25, n. 3, March 21, pp. 574-582. [2] B. Lehman and A. J. Wilkins, Designing t mitigate the effects f flicker in LED lighting reducing risks t health and safety, IEEE Pwer Electrn., magazine, vl. 1, n. 3, Sept. 214, pp. 18-26. [3] C.L. K, T. J. Liang, K. H. Chen and J. F. Chen, Design and implementatin f high frequency AC-LED driver with digital dimming, In: Prc. IEEEInternatinal Sympsium n Circuits and Systems, 21, pp. 3713-3716. [4] C. S. M, Y. J. Chen and W. C. Yang, An efficient driver fr dimmable LED lighting, IEEE Trans. Pwer Electrn., vl. 27, n. 11, Nv. 212, pp. 4613-4618. [5] J. M. Alns, J.Vina, D. G. Vaquer, G. Martinez, and R. Osri, Analysis and design f the integrated duble buck bst cnverter as a high-pwer-factr driver fr pwer-led lamps, IEEE Trans. Ind. Electrn., vl. 59, n. 4, pp. 1689 1697, April 212. [6] G. C. Jane, C. C. Su, H. J. Chiu and Y. K. L, High-efficiency LED driver fr street light applicatins,in: Prc. IEEE Internatinal Cnference n Renewable Energy Research and Applicatinms and Applicatiystce nnai, TamilNadu, INDIAs, Nagasaki, Japan, 212, pp. 1-5 [7] S. Hariprasath and R. Balamurugan, A valley-fill sepic-derived pwer factr crrectin tplgy fr LED lighting applicatins using ne cycle cntrl technique, In: Prc. IEEE Internatinal Cnference n Cmputer Cmmunicatin and Infrmatics. Cimbatre, India 213, pp. 1-4. [8] M. Kumar, L. Parsa, Dual-purpse ffline LED driver fr illuminatin and visible light cmmunicatin, IEEE Trans. Ind. Appl., vl. 51, n. 1, Jan./Feb. 215, pp. 46-419. [9] Y. N. Chang, H. L. Cheng, C. A. Cheng, C. H. Chang and Y. H. Lin, An LFPWM dimmed LED driver featuring high pwer factr, In: prc. IEEE Internatinal Cnference n Industrial Technlgy, Seville, Spain 215, pp. 914-919. [1] A.T.L. Lee, H. Chen, S. C. Tan and S. Y. Hui, Precise dimming and clur cntrl f LED systems based n clur mixing, IEEE Trans. n Pwer Electrn., vl. 31, n. 1, Jan. 216, pp. 65-8. [11] B. M. Lim, Y. H. K, Y. S. Jang and O. H. Kwan, A 2 V 98.16%- efficiency buck LED driver using integrated current cntrl t imprve current accuracy fr large scale single string LED backlighting applicatins, IEEE Trans. Pwer Electrn., vl. 31, n. 9, Sept. 216, pp. 6416-6427. [12] M. H. Rashid, Ed., Pwer Electrnics Handbk. Amsterdam, The Netherlands: Elsevier, 27.