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greenpowerZONE Products for the week of June 15, 2009
Power Integrations Says…
92%-Efficient Power Supply for LED Streetlights up to 150 W
LED Design Simplified Using PI's HiperPLC Controller IC and PI Expert Software
Power Integrations has released a new engineering report (DER-212) describing a 92%-efficient power supply for LED streetlight applications. The design utilizes Power Integrations' HiperPLC power supply controller, which enables a simple, cost-effective circuit design by combining power factor correction (PFC) and resonant (LLC) control functions on a single integrated circuit.
LEDs are rapidly emerging as the preferred streetlighting technology, displacing traditional technologies such as high pressure sodium (HPS) lamps. LEDs consume far less electricity for each lumen of useful light emitted, delivering as many as 80 lumens per watt when driven by a high-efficiency resonant power supply, versus just 58 lumens per watt for HPS lamps. In addition, LEDs provide better directional control and color quality than HPS lights, an important consideration in shopping and residential areas. LEDs can also turn on and off instantly and retain their efficiency when dimmed - features well suited to automated sensing of ambient light and human activity, allowing light output to be optimized for cost, with minimal consequences to the community lighting scheme. Maintenance costs, and therefore the total cost of ownership, are also significantly reduced due to the intrinsically high reliability of LEDs compared to HPS lamps.
HiperPLC, Power Integrations' first high-power product, is designed to control AC-DC converters from 80 to 600 watts. HiperPLC minimizes costs by reducing the size of the PFC magnetics required, and by combining the PFC and LLC controllers into a single IC. The IC provides up to 0.99 power factor and features synchronization of PFC and LLC controllers. Synchronization reduces the ripple in the bulk capacitors, which reduces capacitor operating temperature and significantly extends the life of the power supply. Support for HiperPLC is now featured in Power Integrations' PI Expert software (version 7.1.4), an automated power supply design tool based on PI products.
Comments Doug Bailey, Power Integrations' vice president of marketing: "Municipalities around the world are finding that LEDs offer a greener, more economical approach to streetlighting by saving both energy and maintenance costs. However, these benefits cannot be fully realized without a highly efficient, reliable power supply driving the LEDs. With HiperPLC, designers can produce a simple, reliable, cost-effective, power supply with efficiency as high as 92%."
References
- DER-212:150 W Power Factor Corrected LLC Power Supply Using HiperPLC (PLC810PG), Power Integrations (5/11/09).
- Power Integrations' LED Lighting Microsite.
EN-Genius Says…
As HBLEDs begin to mature enough to be practical for street lighting applications, their environmental benefits, lower operating costs (around 50% less power for an equivalent HPS light) and the lower maintenance costs are making them an increasingly compelling choice for municipal and institutional settings. PI’s rugged and efficient controller should help further accelerate their adoption by reducing both production costs and simplifying the design process. Since street lights present several unique requirements not found in most other LED lighting applications Power Integrations was very smart to address them with their high-power controller plus a set application-specific tools and deeply-detailed design guidelines.
Power Integrations says that they developed their reference design because the power supply element of an HBLED streetlight requires a more sophisticated topology than the average lighting application to achieve maximum efficiency. They have also emphasized reliability in their design, a feature that should help LED streetlights offset their somewhat higher initial costs with significantly less frequent service intervals. The resonant half-bridge topology they chose to use carries the added advantage that it can be implemented with a minimum of low-cost external components.
The resonant half bridge differs from a conventional half bridge because it forms a resonant circuit that switches at the zero crossing which virtually eliminates switching losses (although not conduction losses), enabling typical efficiencies of 96% - 97%. This is essential to keep the overall system efficiency above 90% when working downstream from a power factor correction controller (PFC) whose typical efficiencies run around of 95% - 96%.
PI’s supply controller integrates both the power supply switching regulator and a continuous conduction mode (CCM) PFC circuit. Putting them on the same chip helps reduce BOM costs and, nearly as important, makes it easier to synchronize both blocks’ switching frequencies. Keeping both stages frequency- and phase-locked with a slight offset reduces the sum of the current ripple the bulk capacitor sees, allowing you to use a smaller, lower-cost components. Offsetting the PFC’s switching edge from the output stage also helps eliminates beat frequencies between the two stages and keeps both elements from conducting at the same time: which would produce larger current spikes and more EMI on the input line.
As one would expect with a controller used for high-power, hi-rel, outdoor applications, PI has included several protection features to handle hostile environments, over-current conditions and other indignities. To handle the sweltering temperatures a controller might encounter in, say, Phoenix, Arizona, the reference design is rated to run in ambient temperatures of 65ºC. It is also capable of operating happily with a wide range of supply voltages and frequencies (140 Vac to 264 Vac, 50 - 60 Hz) that qualify it for operation on about 99% of the world’s electrified streets.
To avoid unnecessary transient-induced interruptions, the primary over-current detection circuit waits for 6 - 7 cycles to see if the condition goes away before going through a reset cycle to clear the fault. In the event of a hard short circuit, the protection mechanism shuts down immediately and then attempts an auto re-start. Although they did not go into detail, Power Integrations says that there is additional self-protect electronics to prevent any damage if the short persists.
 PI has done a great deal to make it easy for you to adapt their controller to your particular application – even if you are not familiar with the resonant half-bridge topology. Their support includes several reference designs and a their PI Expert design tool which provides component values and a detailed prediction of your circuit’s performance based on a few basic starting parameters.
Power Integrations has provided the ingredients for a cost-effective supply that can drive an LED array from a wide range of mains voltages while meeting stringent operating temperature and reliability requirements. In doing so, they will enable lighting manufacturers to quickly enter the solid-state street light market: a market which I expect will enjoy steady and significant growth for at least the next decade.
DER-212 Report
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