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LED street lighting enables lower GHG emissions

Posted: 13 Jan 2015     Print Version  Bookmark and Share

Keywords:Greenhouse Gas  GHG  LED  Solar LED street lighting  DC to DC converter 

Our Earth environment is seeing some considerable effects of greenhouse gas (GHG) emissions on our climate and the world is not doing enough to slow this effect down. Our scientists and engineers need to look at energy efficiency and alternatives in order to make a first order affect upon this troublesome issue.

Studies1 show that moving street lighting to LED lead to a 64% energy savings but moreover, the environmental impact on GHG emissions from Power plants would be 33,192 fewer tons of equivalent carbon dioxide (tCO2e) into our atmosphere each year.

China efforts
The Taiwanese government has created a policy to subsidise LED lighting on roadways in order to conserve energy and limit GHG emissions. A 2009 to 2011 study2 showed that the replacement of Mercury Vapor lighting by LEDs could cut electricity usage in half.

In China, there has been development of a DC to DC converter for Solar LED street lighting3. The designers made use of two converters: One for battery charging during the sunlight of the day and the other to supply power to the LED street light from the battery during the nighttime hours.

Development has also been done in Taiwan4 using a single-stage high-power factor (HPF) LED driver with coupled inductors for street lighting. The driver integrates a dual buck–boost ac–dc converter using coupled inductors inside, running in the discontinuous conduction mode DCM) which allows a higher Power Factor (PF) and a half-bridge-type LLC dc–dc resonant converter that has soft switching for a pair of power switches and output rectifier diodes to reduce their switching losses, in a single-stage-conversion circuit topology. This circuit has been shown to have almost 90% efficiency.

There have also been two new efforts in this area recently by Power Integrations and Fairchild.

Power Integrations
Recently, Power Integrations has created a reference design for high power LED street lights as well. Their new design, RDR-382, starts with a constant current, 43 V (nominal), 150 W reference power supply for 90-265 VAC solid-state lighting, and uses Power Integrations HiperPFS-2 PFC controller ICs and HiperLCS integrated LLC power stage ICs.

Most conventional dual-stage drivers that have separate PFC and LLC stages, produce a constant-voltage (CV) output requiring multiple DC-DC converters to convert the output to constant current (CC). This latest reference by Power Integrations designers uses a neat feedback and control scheme that lets the LLC provide a constant current directly at the output. This results in a one-third reduction in component count and increases efficiency to better than 93 %, plus manages to eliminate the DC-DC converter stage to significantly reduces size. The high nominal 250kHz LLC switching frequency reduces the size of the required magnetics, coupled with the use of a continuous-conduction-mode, variable-frequency PFC stage that enables reduction of EMI in contrast to fixed-frequency alternatives.

This reference design can drive single or multiple LED strings and allows analogue dimming to be controlled with a 0-10 VDC input.

The Fairchild application note is a 150W rating design guideline for LED street lighting. The circuit architecture consists of Critical Conduction Mode (CRM) Power Factor Correction (PFC) and LLC Series Resonant Converter (SRC) with high power factor and high power conversion efficiency using FL7930B, an active PFC controller for boost PFC applications that operate in critical conduction mode and FAN7621S is a pulse frequency modulation controller for high efficiency half-bridge resonant converters. An in-depth overview of this design is in Fairchild AN-9738. This application note discusses the basic operation of the Boundary Conduction Mode (BCM) PFC Pre-regulator, the consideration of the LLC Resonant Converter use in this architecture, and greatly, step-by-step design considerations with a full Bill of Materials (BOM), schematic and data sheets. Fairchild has really delivered a great tutorial here for power designers.

The CRM PFC converter is shown in the front end and the LLC SRC DC-DC converter in the back end. FL7930B and FAN7621S are able to achieve high efficiency with medium power for 150W rating applications where CRM and LLC SRC operation with a two-stage shows best performance.

Since it was first introduced in early 1990s, LLC-SRC (series resonant converter) has become a popular topology because of its outstanding performance in areas such as the output regulation of switching frequency, Zero Voltage Switching (ZVS) capability for the entire load range, low turn-off current, uses small resonant components with the integrated transformer, zero current switching (ZCS), and no reverse recovery loss on secondary rectifier.

1 LED street lighting as a strategy for climate change mitigation at local government level, Garcia, Roberto Barraza, Departamento de Ingeniería Civil y Ambiental, Universidad Autónoma de Ciudad Juárez, Mexico; Angulo, Gilberto Velazquez ; Gonzalez, Jaime Romero ; Tavizon, Edith Flores ; Cardozo, Jose Ignacio Huertas, 2014
2 Assessment of energy-efficient LED street lighting through large-scale demonstration, Su-Chin Huang ; Ind. Technol. Res. Inst., Hsinchu, Taiwan ; Li-Ling Lee ; Ming-Shan Jeng ; Yao-Ching Hsieh 2012
3 Study of a DC-DC Converter for Solar LED Street Lighting, Chia-Ching Lin, Lung-Sheng Yang, and En-Chih Chang, 2013
4 A Novel Single-Stage High-Power-Factor LED Street-Lighting Driver With Coupled Inductors, Chun-An Cheng, Member, IEEE, Hung-Liang Cheng, Member, IEEE, and Tsung-Yuan Chung, 2014

About the author
Steve Taranovich is a senior technical editor at EDN with 41 years of experience in the electronics industry. Steve received his MSEE from Polytechnic University, Brooklyn, New York, and his BEEE from New York University, Bronx, New York. He is also chairman of the Educational Activities Committee for IEEE Long Island. His expertise is in analogue, RF and power management with a diverse embedded processing education as it relates to analogue design from his years at Burr-Brown and Texas Instruments.

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