Development of Pulse Width Modulation LED drive

Transcription

1 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC Developmen of Pulse Widh Modulaion LED drive YuanPiao. Lee 1 ShihKuen. Changchien 2 ChainKuo Technology Universiy, Changhua, Taiwan, ROC 1,2 Absrac In his paper, a highefficiency LED driver circui curren conrol mode. The advanages of LED energy saving, long life, easy o drive, ec., has become he ligh source of mos value. Bu because of he elecrical characerisics of each LED is easily affeced by he emperaure differences, making a rapid increase in he curren flowing hrough which herefore lead o he LED driver circui is easy o burn. To solve his problem, many expers and scholars have made a lo of pracice, one of he mos effecive ways o improve his problem based on he use of a consan curren o drive. Despie recen years, many researchers have focused on he design of he LED driver circui, he LED dedicaed drive circui have mushroomed developed, bu his specific driver circui price is sill oo high, i is necessary o more lowcos way o achieve in order o mee he large number of applicaions in he LED. Due o he characerisics of he PULSE WIDTH MODULATION conrol is excellen and inexpensive; he design is expeced o become he mainsream. In his paper, he consan curren LED driver circui using PULSE WIDTH MODULATION design wih dimming funcion. Keywords: driver circui, consan curren, PULSE WIDTH MODULATION dimming. I. INTRODUCTION The LED's energy consumpion is low, and he conrol of is brighness is simple and effecive.[1] As a new generaion of environmenal ligh source, LED has been widely used in many areas because of high efficiency, low driving volage, low power consumpion, long life and oher characerisics.[2] in addiion, Lighemiing diodes (LEDs) are he major backlighing source used in liquid crysal displays.[3] In order o ge high efficiency of LED drive circui, somebody presens a mode dimming LED driver based on buck DCDC converer or wo sage ACDC lighemiing diode (LED) driver. [4] [5] Anyway, LED semiconducor elemen is driven by DC, he brighness is almos proporional o he curren flow hrough, and general ligh sources, as can wihsand he power are limied. The use power exceeding reasonable limis may cause he LED's burned. LED manufacured using he maerial properies and he differences in he manufacuring process, so ha even he same ype of he LED forward volage 158

2 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC and inernal resisance characerisics canno be exacly he same, hus he same as he make he brighness of he LED, so he LED drive circui design is very imporan. Pas early in he LED driver circui, mainly o use he limiing resisor ways o achieve, as shown in Figure hree ypical common drive circui. (A) parallel LED driver circui, designed o ake general limiing resisor R1 = R2 =.... = RN, bu due o he supply of he DC drive volage (Vin) will be he characerisic differences beween he changes, and various LED, so canno be consisen wih he curren hrough each LED. Figure 2 he radiional resisive ype LED driver circui in series. All LED series, his circui if he LED series feaures large difference in volage will be allocaed on boh ends of he volage of each LED is no he same, bu ensure he flow are he same on all LED curren herefore, he brighness of each LED will be he same. The disadvanage of his circui is ha he LED is used in andem, i is required for he DC drive volage, an LED damaged, he whole sring LED will no operae. Shown in Vin LED 1 LED 2 LED N R1 R2 RN Figure 1 he radiional resisive LED drive circui in parallel The Figure 1 he radiional resisive LED drive circui in parallel, each sring is only one LED effec is poor. Laer by modified, Figure 2 he radiional resisive ype LED driver circui in series. All LED series, his circui if he LED series feaures large difference in volage will be allocaed on boh ends of he volage of each LED is no he same, bu ensure he flow are he same on all LED curren herefore, he brighness of each LED will be he same. The disadvanage of his circui is ha he LED is used in andem, i is required for he DC drive volage, an LED damaged, he whole sring LED will no operae. Vin LED 1 LED 2 LED N R1 Figure 2 he radiional resisive ype LED driver circui in series When andem drive very muliple LED driver you need quie a high DC volage If you do no wan o improve he DC drive volage, you can adop a seriesparallel hybrid drive has been. In Figure 3 he radiional resisive LED seriesparallel hybrid drive circui, alhough he combinaion of he advanages of he firs wo, bu sill 159

3 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC exiss LED curren canno be exacly he same as he DC drive volage higher shorcomings, he need o make furher improvemens. Addiion o he above LED driver circui, here are sepdown or sepup circui capaciance of series and parallel, charge pump (Charge Pump) swiching DC / DC converer as LED drive circui archiecure. Which highfrequency swiching DC / DC converer way, due o he small size, high efficiency, consan curren conrol is easy, and is very suiable for use in highpower illuminaion LED driver. Highfrequency swiching DC / DC converer Buck, Boos, BuckBoos, Flyback, Forward converer basic power conversion circuis for LED driver circui design. Bu among his power conversion circui, he boos converer simple circui archiecure as well as he advanages of easy power swich driver, i is ofen used in LED drive circui, and a large number of dedicaed IC available. As he curren is sill high, he price of hese LED driving circui IC dedicaed Therefore, his paper aemp o applicaion of curren mode PULSE WIDTH MODULATION conrol as he use of he conrol circui of he LED drive circui o reduce he cos of he drive conrol circui. Curren mode PULSE WIDTH MODULATION conrols is excellen feaures and low price, i is widely favored by he indusry and academia is exremely suiable for he power converer conrol circui, herefore we choose his as major design applicaions. Vin LED 11 LED 12 LED 1N LED 21 LED M1 LED 22 LED M2 LED 2N LED MN R1 R1 R1 Figure 3 he radiional resisive LED seriesparallel hybrid drive circui II. CURRENT CONTROL MODE PULSE WIDTH MODULATION Commonly used in he power converer on pulse widh modulaion of volage conrol mode or curren conrol mode echnology. As shown in Figure 4 he pulse widh modulaion and Figure 5 he pulse widh modulaion principle. V ref kvo V conrol E/A Comp Sawooh Waveform or Inducor curren Figure 4 he pulse widh modulaion III. PULSE WIDTH MODULATION PRINCIPLE Is basically composed by an error amplifier (Error Amplifier; E / A) and a comparaor. The posiive inpu of he error amplifier is usually a highprecision DC reference volage V g 160

4 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC (Vref), and he oupu volage via a volage dividing circui, will be assigned o he volage (KVO) is conneced o he negaive erminal of error amplifier inpu pin, and he differenial volage generaed by he wo inpu erminal, amplified by he gain of he error amplifier o generae he oupu volage signal (Vconrol). Vconrol Vg Figure 5 he pulse widh modulaion principle Vconrol Vg Figure 6 Duy Cycle of he change in he load changes: Load becomes smaller; he duy cycle is also followed smaller Vconrol Vg Figure 7 Duy Cycle of he change in he load changes: Load becomes large; he duy cycle is also followed larger Vconrol signal wih a sawooh signal (his is he volage conrol mode) or he inducor curren (his is he curren conrol mode) signal comparison, he oupu of he comparaor will generae a pulse wave signal, and power swiching elemen can be driven direcly via he drive circui, his is known as pulse widh modulaion principle. The Figure 6 Duy Cycle of he change in he load changes: Load becomes smaller; he duy cycle is also followed smaller. Redline Vconrol signal when he seady sae, when he load becomes small, he Vconrol signal decreased o green lines shown posiion, afer comparison wih he sawooh signal comparison, shows ha he duy cycle as he load becomes smaller and smaller, so adjus he oupu volage o mainain a sable volage. The Figure 7 Duy Cycle of he change in he load changes: Load becomes large; he duy cycle is also followed larger. In he red as Vconrol when he seady sae signal, and when he load becomes small, he Vconrol signal fell o he blue line shows he posiion, as compared by he comparaor wih he sawooh signal, found ha he duy cycle as he load becomes large become larger, adjusable oupu volage o mainain a sable volage. IV. LED DRIVER CIRCUIT DESIGN The Figure 8 he applicaion of curren conrol mode boos power 161

5 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC conversion. Where PULSE WIDTH MODULATION conrol he aforemenioned curren conrol mode, he negaive erminal of he error amplifier inpu volage signal, he volage signal oupu volage (Vo) via parial pressure sampling resisor R1 and R2 share. The posiive erminal of he comparaor inpu inducor curren signal from he inducor curren flows hrough he curren deecion resisor (Curren Sense Resisor) Rs achieved. In general, he inducor curren signal ofen due o he swiching acion of he drive power, insananeous flow hrough he parasiic elemens of he swiching elemens (Parasiic Elemens) curren or power diode reverse recovery ime caused by, so ha he Rs volage noise, shown in Figure 9 he inducor curren noise suppression mehod. This will cause conrol problems, and lead o sysem insabiliy. In order o inhibi his curren noise, he mos simple and mos commonly used mehod o join an R, C, composed of he lowpass filer. The R and C circui as shown in Figure 8 he applicaion of curren conrol mode boos power conversion. The high frequency curren noise filered In addiion, in order o avoid his problem. In small power applicaions, since he inducor curren flows hrough Rs, he loss of power will be made, so he efficiency is poor. Try no o use his aricle Rs, in order o improve he conversion efficiency of he LED driver circui, he circui diagram shown in Figure 9 he inducor curren noise suppression mehod. V s Driver L A Q Compensaion Nework #2 Comp V g PWM Curren Mode Conroller R s D Vo V ea o A (Inducor curren) Co Compensaion Nework #1 E/A Figure 8 he applicaion of curren conrol mode boos power conversion V s L Q R R s Figure 9 he inducor curren noise suppression mehod D Vo Co Vref V. CIRCUIT DESIGN AND EXPERIMENTAL RESULTS The Figure 10 he dimming funcion applicaion UC3843 Boos converer LED driver circui. Figure VI for his applicaion UC3843 designed wih dimming funcion boos converer LED driver circui. The dimming LED driver circui works are described as C RL RL R1 V R2 162

6 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC follows: 1. When he UC3843's Vcc (Pin 7) is abou 6 ~ 7V IC sars is operaion, Pin 5V reference volage is generaed immediaely. 2. The 5V reference volage is generaed; supply of he chargedischarge circui composed by he RT and CT, and may deermine he swiching frequency of he circui. 3. Pin 2 of he feedback volage signal from he 5V volage reference, hrough R1, R2 and a variable resisor R3 parial pressure decision. Highly anicipaed he from feedback volage of he bi level o adjus he duy cycle o achieve he purpose of dimming. 4. Pin 4 of he signal waveform of he RT and CT charge and discharge, afer he charge and discharge ime consans have been suiably seleced, so ha he waveform of he riangular wave, an approximaion Afer Q1 and he variable resisor R5 of he signal feedback o Pin 3, o simulae inducor curren waveform. Because i was no he acual use of he curren sensing resisor, so he efficiency can be improved, his is a conribuion o one of he circui. By he curren feedback signal level o adjus he duy cycle o achieve dimming purposes. 5. The C1 larger capaciy elecrolyic capacior, o provide IC Pin a sable DC volage. C2 is generally small ceramic capaciors for highfrequency noise filer IC DC power o preven IC malfuncion, also known as decoupling (Decoupling) capaciors. 6. The C3 Pin 8 of 5V reference volage decoupling capaciance, and is role wih C2. 7. The Rg for an approximaely Ω o several ens Ω grade resisance, wih he parasiic capaciance of he power swich an RC chargedischarge circui is formed for easing he driving signal, o avoid generaing excessive noise. R6 is ens of kω grade resisors, for changing he impedance of he conrol inpu erminal of he power swich, o avoid driving signal due o noise, is oo large, resuling in a large volage, while he power swich is breakdown damage. R1 R3 R2 Vs R4 Error AMP Adjus R5 Q1 L Vg RT I SENSE Adjus CT S Comp Vref 1 8 C3 V FB V 2 7 i I SENSE Oupu C2 3 6 R T/C T 4 D Vo UC Co GND Figure 10 he dimming funcion applicaion UC3843 Boos converer LED driver circui Vs C1 Rg R6 To validae he proposed boos converer wih dimming funcion UC3843 design based LED driver circui, he acual design of a drive 5 LEDs in 163

7 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC series of prooype circui. Please refer o Figure 11 he average inducor curren wave 20.36mA (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5uS/div), Figure 12 he average inducor curren wave 15.21mA (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5uS/div), Figure 13 he average inducor curren wave 10.54mA (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5uS/div), Figure 14 inducor curren average of 6.13mA he wave (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5uS/div), and Figure 15 inducor curren average of 1.03mA he wave (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5mS/div). Known by one LED average curren 20.36mA ma ma 6.13 ma, he circui operaes in coninuous conducion mode (Coninuous Conducion Mode; CCM), as shown in Figure 7 ~ Figure en shows. While he minimum brighness ligh load, as shown in Figure 11, he average LED curren 1.03mA when he circui is operaing in disconinuous conducion mode (Disconinuous Conducion Mode; DCM). Special circui of Figure 15 in disconinuous conducion mode waveforms, he load is quie small (average LED curren o 1.03mA), he UC3843 has enered he socalled inermien operaion mode (Burs Mode) o reduce operaing frequency, and hus enhance he conversion efficiency. Figure 11 he average inducor curren wave 20.36mA (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5uS/div) Figure 12 he average inducor curren wave 15.21mA (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5uS/div) Figure 13 he average inducor curren wave 10.54mA (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5uS/div) Figure 14 inducor curren average of 6.13mA he wave (Ch1: 20V/div, Ch2: 164

8 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC V/div, Ch3: 20mA/div, Time: 5uS/div) inducor curren dimming 20.36mA. From he phoos, you can clearly observe he effec of he dimming circui. VI. CONCLUSION Figure 15 inducor curren average of 1.03mA he wave (Ch1: 20V/div, Ch2: 10V/div, Ch3: 20mA/div, Time: 5mS/div) Figure 16 he phoo in he average inducor curren dimming 1.03mA This paper presens a high efficiency LED driver circui using curren conrol mode PULSE WIDTH MODULATION design. Measured by he amoun of he acual circui, he research of his aricle has good dimming funcion. In addiion, he circui designs of his aricle, in he curren feedback signal, ry no using curren sensing resisor, o improve he conversion efficiency on low power oupu applicaions. The dimming circui does no use a curren sensing resisor, so he expense of he curren feedback pah of he response, we are unable o mainain he fas response of he original curren conrol mode, his problem will be he goal of fuure improvemen. In addiion, he oupu power of he drive circui is smaller in he fuure is expeced o coninue o une his mehod for large oupu power, in order o direcly applied o he highpower LED. Figure 17 he phoo in he average inducor curren dimming 20.36mA Figure 16 he phoo in he average inducor curren dimming 1.03mA. Figure 17 he phoo in he average REFERENCE [1] Can Zhang, Huibin Qin, and Liyang Qu, "Led Dimming Sysem of Wireless Remoe Conroller." 2012 Inernaional Conference on Image Analysis and Signal Processing (IASP), pp. 14,

9 ISSN , Inernaional Journal of Technology People Developing, Vol. 2, No. 3, DEC [2] Chen Zhiliang, Tian Liguo, Li Meng, Zhang Jieping, and Wang Yongliang, "Led Toning Sysem Based on Nrf24l01 Wireless Conrol." h Chinese Conrol and Decision Conference (CCDC), pp , [3] Y. T. Hsieh, and Y. Z. Juang, Analysis and Suppression of Overcurren in Boos Led Drivers, Journal of Display Technology, vol. PP, no. 99, pp. 18, [4] Tong Zhang, Yuan Yang, Zhenghua Song, and Yongbo Fan, "A Dual Mode Dimming Whie Led Driver Based on Buck DcDc Converer." 2012 Inernaional Conference on Compuer Science and Informaion Processing (CSIP), pp , [5] F. Zhang, J. Ni, and Y. Yu, High Power Facor AcDc Led Driver wih Film Capaciors, IEEE Transacions on Power Elecronics, vol. PP, no. 99, pp. 11,