LED Flood and Street Lights in Urban Design: Considering its Compliance with Technical Requirements in the Design and Implementation of the Control Gear

Use of LED light sources in urban lighting have grown substantially and have attracted so much attention. Due to the increasing utilization of LED floodlights and LED streetlights in urban lighting, observing the technical points and realization of the standard requirements in design of different parts of LED light sources should be taken into consideration. A Typical LED light source consists of different parts such as LED module, control gear, heat sink, optical and mechanical parts. It should be pointed out that the significant LED features such as low power consumption, long lifetime and acceptable light quality are not achievable unless the technical requirements to be considered in design of control gear. Therefore, appraising the technical specifications of a control gear or LED driver and improve them are very essential. Among different types of control gears for driving LED modules, the switching mode control gears with constant current output is of great interest. In the other words, the amount of luminous flux and the quality of generated light cannot be correctly predicted by applying a constant voltage control gear. While the current constant control gear can be used to have a desired luminous flux and light quality in spite of temperature variation or input voltage change. In this paper, technical specifications and various stages of a constant current LED module control gear which has been built in Afratab Electronics Industry Co. have been illustrated. This control gear with the rated power of 65W is a switching mode control gear with constant current output. This control gear has been used to drive an LED module consisting of 60 series connected high power LEDs. At input voltage of 230 VAC the measured output voltage of 187 V and the measured output current of 343.6 mA have been obtained. Having change in the input voltage of control gear form 230 VAC to 260 VAC leads to only 0.17% change in current output. Furthermore, having change in the input voltage from 230 VAC to 170 VAC leads to less than 0.06% change in current output. Therefore, a current constant output control gear is realized in spite of changing the input voltage from 170VAC to 290 VAC. In addition, having reduction in the number of LEDs series from 60 to 55 (8.3% reduction in load of LED module) results only a 3.3% increase in current output of control gear. The built control gear also includes the main parts of the protection circuit and EMI input filter, Boost power factor correction and constant current LED module driver which are applicable in the range of input voltage and load change. The EMI input filter has been used to eliminate the common mode and differential mode noise. In other words, it prevents noise transmission from the utility to the circuit and vice versa. Moreover, the protection circuit protects the control gear from fault conditions such as excessive currents, inrush currents and excessive transient voltages. The power factor correction stage uses the Boost topology. This stage made the input current circuit nearly sinusoidal and in phase with the mains voltage. The measured power factor (PF) of this control gear is more than 0.96 and the total harmonic distortion (THD) of the input current is less than 10% at rated voltage of 230VAC. Unlike the drivers and power supplies without power factor correction stage, sharp peaks in current waveform and non-sinusoidal input current waveform with high (THD) does not exist in this control gear and the current waveform is quasi-sinusoidal with very low harmonic distortion components. In addition, the requirements of class C of IEC61000-3-2 are completely realized. For driving the LED module with appropriate current and voltage, the modified Buck topology has been applied. This stage is a step-down switching mode circuit and control on time and off time of the power switch to generate a constant current for LED module. Adjustable current output in accordance with the specifications of the LEDs used in LED module is another characteristic of this circuit. Because of the chosen integrated circuits and the operation of them based on switching mode, high efficiency is also another feature of this control gear.