A review of best practice in developing efficient power supply solutions for solid state lighting
The LED lighting market looks set to explode, with some sources predicting that in five years time 50% of the global lighting market will be fulfilled by solid state solutions. Whether street or office illumination, refrigeration or architectural lighting, every solid state light needs power – and the power supply is often the weakest link.
By Cor van Dam, Marketing Director, Power, Avnet Abacus
Whilst the LEDs themselves are highly efficient, the benefits of this can be lost if energy efficiency is not optimised in the power supply. Correctly installed, the lifetime of an LED light can be 35 years or more, but even a well-designed power supply working within its operating parameters will last only 10-12 years. A poorly designed, lower efficiency power supply unit running at high-temperature will not even last half as long. Designing a power supply unit to achieve maximum operating efficiencies for LED lighting applications can be a daunting task. Designers have to consider a wide range of issues when conceiving power solutions to navigate the regulations for LED installations and ensure a power supply with maximum service life.
Due to specific operating voltages and the configuration in which the LEDs are arranged, a standard power supply cannot be used with LED lighting. LED power supplies are governed by specific legislation covering safety (EN61347-1/ -2-13, UL8750, UL1310 Class 2), EMC (EN55015) and harmonics (EN61000-3-2 Class C), but not all these specs are relevant to lighting applications. In addition, the EU Ecodesign Directive 2009/125/EC sets out rules for reducing the environmental impact of Energy-using Products (EuP) and other Energy related Products (ErP) at all stages from design concept to manufacturing. Street, office and domestic lighting all fall within this directive, along with their respective power supplies. This legislation can sometimes be complicated to interpret for lighting designers and LED engineers entering the market, so discussing specific requirements with a specialist distributor such as Avnet Abacus with its comprehensive power portfolio and consultative approach can be valuable at the design stage to ensure compliance from the start. In addition, a good distributor will work with its suppliers to keep up with future regulations and participate in regular training. Designers have to consider a wide range of issues when conceiving power solutions to navigate the regulations for LED installations and ensure a power supply with maximum service life.
The illumination output of solid state systems depends on how the LED array is driven. For example, using a constant current power supply produces the lowest cost and highest efficiency solution, but unbalanced current for each parallel branch of LEDs can lead to uneven brightness and shortened life. On the other hand, using a constant voltage power supply with an LED driver IC will accurately control the current through the LEDs, delivering a more uniform light output and long life, but at a reduced efficiency and a higher cost. Designers will need to consider what application they are designing for and if a return on investment could be achieved by using a more expensive, but more uniform driver solution to give extended life, instead of a low cost, reduced life option.
For example, for small and medium power LED Lighting systems, sophisticated semiconductor solutions from Power Integrations (PI) could be specified. PI leads on technology solutions to design customised LED power supplies with the minimum of component with their perfect working software tools. This could be a low cost option for large volume applications, and one benefit is that the circuit can be trimmed for the highest efficiency. However, this is not always the option with the fastest turnaround time, given the approval process required for some regulations.
The alternative is a ready to use, high quality, high efficient off the shelf solution resulting in a faster time to market. Typically we have over 500 different models available with constant current (CC) output power 3W up to 350W, and a growing number with dimming options for use in applications such as architectural lighting. In addition, a wide range of LED power supplies with constant voltage (CV) output are available, ranging from 10W to thousands of Watts, suitable for low to high power LED lighting systems and screens.
Maximising Service Life
Much has been written about the longevity of LEDs, but it is important to be aware that they are not indestructible; a simple voltage glitch has the capacity to damage the LED. Aside from that, the main area affecting service life of both the power supply and LED lighting is that of excess heat.
Although the LED devices run at low power, the build up of heat in the array as well as in the power supply needs to be minimised by using heat sinks on mountings for example. Not only will the lighting unit run more efficiently at a lower temperature but the risk of damage to the housing holding the LEDs will be significantly reduced. Designers should be integrating heat dissipation solutions into the power supply design from the outset in order to maximise service life. Consideration should also be given to where and how the lighting units will be mounted to aid the cooling process.
Another issue to weigh up is minimising weak points within the power supply assembly itself. Components such as electrolytic capacitors and opto couplers are known to impact on service life and reliability. Increasingly, designers are specifying power supply solutions without these items. In addition, care should be taken to ensure that high quality construction methods are used to prevent against the potential degradation caused by heat, aggressive moisture ingress and UV light. A dry solder joint from poor quality construction methods could prove critical once the power supply is in the field.
Selecting a power supply for LED lighting applications is not straight forward, and not everyone will have the in-depth knowledge of the rules and regulations that must be complied with in each specific market. In order to achieve the longest life cycle possible with LED lighting, it is crucial to get the right advice and specify and select the correct power supply from the many solutions available and install it correctly. Only when all these things have been taken into consideration can you expect to achieve the most efficient solution possible.
Learn How to Achieve Efficient Power Solutions with Avnet Abacus
As one of Europe’s leading power, interconnect, passive, and electromechanical distributors, Avnet Abacus is teaming up with some of the world’s leading manufacturers of power components to deliver a series of free technical seminars in five locations across Europe focused on the difficult challenges that face power system design engineers.
In the one-day sessions, Avnet Abacus and its franchises Aimtec, Cymbet, Emerson, Enpiron, Excelsys, Murata Power Solutions, Power Integrations, and Schaffner will provide an overview of environmental and energy efficient directives impacting power supply design. Explains Cor van Dam, Avnet Abacus’ European Marketing Director: “Efficient use of power is a challenge that affects everyone. There are many issues: new mandatory regulations will require standby (no-load) energy consumption to approach Zero watts; consumers demands that battery-powered devices have a long life between recharging; and LED lighting systems must be powered correctly or the benefits are wasted. Our seminar series will address these topics and many more, and we encourage design engineers to raise their own specific areas of interest during the extensive Q&A sessions with technical representatives from the participating companies.”
There will also be tabletop presentations from leading manufacturers of associated power products including Molex, Pulse and TE Connectivity.
Design engineers are invited to register for the free seminars by visiting www.avnet-abacus.eu or call +44-1628 512940.