Design and Simulation of Boost Converter for RGB LEDs in Lighting System SHRIRAKSHA MANJUNATH NAIK 1, GANAPATHI SHARMA 2 1 M.Tech Student, Department of Electronics and Communication Engineering, Srinivas Institute of Technology Mangaluru, Karnataka, India naikshriraksha497@gmail.com 2 Assistant Professor, Department of Electronics & Communication Engineering, Srinivas Institute of Technology Mangaluru,Karnataka, India sharma746@yahoo.com Abstract The RGB LEDs are used for producing different colours and of different intensities. This paper proposes digital control of the DC-DC converter used to provide the needed constant current for the RGB LEDs. The RGB LEDs have been powered from DC-DC converter. The RGB uses three different voltage sources as each RGB colour requires different drive voltages. The output current is kept constant with the help of the PI controller. The controller is designed such that even though there is variation in input the output will be in steady state. The above model is simulated in MATLAB/Simulink and the results are verified. With 12V supply voltage the efficiencies of RGB LEDs are 93%, 93% and 93% respectively. Keywords DC-DC Converter, RGB LEDs, Controller. I. INTRODUCTION LEDs have been developing over the last few decades from indicator lamp to a light source.led manufacturers are creating a revolution in the world of lighting technology. Compared to other light sources, the LED has some advantages, it is more eco-friendly than cold-cathode fluorescent lamps as they do not contain mercury [1], small size with resistance to vibration and pressure and high speed response.as a result, there is an increase in the use of high performance LEDs in street lighting, parking garage lights, commercial down lighting and some residential applications that validate the performance of LED technology. The arrival of a full colour range of the high power LEDs, more developed architectural designs, studio and stage lighting are progressing. Adding digital control to coloured LEDs has launched a new dimension in architectural lighting; the coloured LEDs significantly reduce power consumption. LED strings can not only be supplied by pure DC currents but also by pulsating currents [2]. In this regard the project, there are three constant current controls for dimming and three different supply voltages [3]. Recent advances in engineering applications have continued to focus developments on greater energy efficiency, longer life and lower environmental impact on many products. Energy management and cost reductions are key tools in commercial lighting. Energy-wasting conventional lighting have been replaced by the eco-friendly LED lighting. II. DC-DC CONVERTER The change in voltage from one level to another is done by an electronic circuit known as DC-DC converter. A DC-DC converter can be used to change the voltage from one level to another. A few applications requires a low DC voltage in that the voltage is stepped down and in some case a higher voltage is required here it is stepped up. In all these we change the dc voltage from one level to another. DC-DC Converters are required to step up or step down the voltage like transformers in AC. therefore we can say that DC equivalent of a transformer is a DC-DC converter. There is no energy manufactured inside the converter the output power all depends upon the input. In fact some of the energy is used by the circuit components while undergoing the process of conversion. III. CONTROLLER CIRCUIT The main objective of the control circuit is to maintain the output voltage and current at required value. To achieve this the output current is sensed in terms of voltage using a current sense resistor. This voltage is compared with reference voltage and an error signal is generated. PI controller is used here. The error signal is compared with the carrier signal and pulse is generated. This pulse is used to vary the duty cycle of the switch. PWM is a popular control method, here the duty cycle is tuned to get the desired brightness level. The more the levels are available, the more colours can be produced [4]. Since applications like outdoor decoration lighting in cities, 838
stage lighting designs, home decoration lighting and LED display matrix are gaining popularity, LCD backlighting and projectors are also found recently by RGB colour mixing. A.BLOCK DIAGRAM current can be measured through voltage and the control techniques can be applied. C. RGB LEDs RGBs are the LEDs which have three colour filaments they are red, green and blue. These three colours require different drive voltages. As a result, three different converters are required to power these LEDs. The forward voltages and currents of RGB LEDs are given in TABLE I. TABLE I Forward and Current of RGB LEDs. Fig. 1 Block diagram of the proposed system Battery is energy storage device. It is used to supply the power to the circuit to which it is connected. The battery always supplies a DC output. The converter converts the unregulated dc voltage to regulated dc voltage from one level to another. Since here boost converter is used the voltage at the output side will be greater than the voltage at the input side. This regulated output from converter is given to the load. Load here is the array of 14 LEDs. The output of the load is taken as input by the control circuit. The controller used here is PI controller. This feedback loop is given to the converter. B. BOOST CONVERTER Forward (V) Forward Current(mA) RED 1.9 350 GREEN 3.028 350 BLUE 2.69 350 Since here an array of 14 LEDs are used, having two parallel branches with each branches consisting of seven series LEDs. The operating voltage or the output voltage Vo is seven times the forward voltage mentioned in the above table and the output current is twice that mentioned above. Thus, the voltage and current driving LEDs are as in TABLE II. TABLE II s and Currents of Boost Converter driving RGB LEDs Forward (V) Forward Current(mA) RED 13.3 700 GREEN 21.196 700 BLUE 18.9 700 D. SPECIFICATIONS The various parameters considered in the design of the three converters to drive red, green and blue LEDs are as showed below TABLE III Specifications of Boost Converter Driving RGB LEDs Fig. 2 Basic Boost Converter Boost Converter is a DC-DC converter for which output voltage is greater than input voltage. When the MOSFET switch is ON, the current through the inductor begins to raise and the inductor starts store energy. When the MOSFET switch is closed, the energy stored in the inductor starts dissipating. The current from the voltage source and the inductor flows through the fly back Diode D to the load. The across the load is greater than the input voltage and is dependent on the rate of change of the inductor current. Thus the average voltage across the load is greater than the input voltage and is determined with help of the duty cycle of the gate pulse to the MOSFET switch. Converters are used to stabilise output voltages, but LEDs require stabilised output currents. By adding a series resistor to LEDs the output Input Switching Frequency Current Ripple RED GREEN BLUE 12V 12V 12V 13.3V 21.196V 18.9V 5KHz 5KHz 5KHz 350mA 350mA 350mA 1% 1% 1% 1)Pulse Width Modulation(PWM): The model for generating digital pulse-width modulation(pwm) is shown in Fig. 3 839
Fig. 3 Circuit for PWM 2) Boost Converter: The basic boost converter circuit consists of a supply, inductor, diode, capacitor and load. Simulink model of boost converter with LEDs as load is shown in Fig.4. Simulink model of closed loop Boost converter is shown in Fig.5 Fig.6 Circuit of closed loop boost converter with variation in input II. RESULTS AND DISCUSSION A. Pulse-width modulation (PWM) Fig. 7 shows the output waveform of the PWM signal. The carrier signal is compared with a dc signal and a PWM signal is obtained. This obtained signal is used for turning ON and OFF the switch. Fig. 7 waveform of the PWM signsl B. Boost Converter Fig.8 shows the output waveform of inductor current, for red colour. Fig. 4 Circuit of Boost Converter Fig.8 waveform of inductor current, output voltage and output current for red colour Fig. 5 Circuit of closed loop Boost Converter with PI Controller Fig. 6 shows the simulink model of closed loop boost converter with variation in input voltage. In this the input voltage is varied. Fig. 9 shows the output waveform of inductor current, for green colour. 840
Fig. 12 shows the output waveform of inductor current, with PI controller for green colour. Fig. 9 waveform of inductor current, output voltage and output current for green colour Fig. 10 shows the output waveform of inductor current, for blue colour. Fig. 12 shows the output waveform of inductor current, output voltage and output current for closed loop with PI controller for green colour Fig. 13 shows the output waveform of inductor current, with PI controller for blue colour. Fig.10 waveform of inductor current, output voltage and output current for blue colour Fig. 11 shows the output waveform of inductor current, with PI controller for red colour. Fig. 13 shows the output waveform of inductor current, output voltage and output current for closed loop with PI controller for blue colour. Fig. 14 shows the output waveform of inductor current, for variation in input with controller for red colour Fig. 11 shows the output waveform of inductor current, output voltage and output current for closed loop with PI controller for red colour 841
Fig. 14 shows the output waveform of inductor current, output voltage and output current for closed loop with variation in input voltage for red colour Fig. 15 shows the output waveform of inductor current, for variation in input with controller for green colour. REFERENCES [1] Jaber Hasan and S. Ang, A High-Efficiency Digitally Controlled RGB Driver for LED Pixels, IEEE Publication 2011 [2] Heinz van der Broeck, Georg Sauerlander, Matthias Wendt, Power driver topologies and control schemes for LEDs, IEEE Publication 2007. [3] Jaber Hasan, Do Hung Nguyen and Simon S.Ang, A RGB- Driver for LED Display Panels, IEEE Publication 2010. [4].Meriam Gay V. Bautista, Wan-Rone Liou and Mei-Ling Yeh, Dimmable Multi-Channel RGB LED Driver, IEEE Publication 2013. [5] Daniel Hart, Power Electronics Converters, Applications and Design, 2nd edition. [6] Ned Mohan, Tore M. Undeland and William P. Robbins, Power Electronics: Converters, Applications, and Design, 3rd Edition, Wiley. Fig. 15 shows the output waveform of inductor current, output voltage and output current for closed loop with variation in input voltage for green colour [7] RGB LED Datasheet, High Power LEDs-Edixeon RGB Series Datasheet, Edison Opto Corporation-2012 Fig. 16 shows the output waveform of inductor current, for variation in input with controller for blue colour. Fig. 16 shows the output waveform of inductor current, output voltage and output current for closed loop with variation in input voltage for blue colour III. CONCLUSION This paper presented the study and design of boost converter. The open loop boost converter, closed loop boost converter with PI controller and boost converter with variation in input were successfully simulated in MATLAB/Simulink. Even though there was variation in input, the output attained its steady state. The theoretical values and the simulated results both were found to match each other satisfactorily. ACKNOWLEDGMENT We would like thank Head of the department of Electronics and Communication and Principal of Srinivas Institute of Technology for their guidance and support. 842