The right resonant power controller can achieve increasingly stringent Energy Star requirements
BY LUCY A. SNYDER
Designing power supplies for products such as telecommunications devices, laptops, game consoles, and LCD and plasma TVs presents increasing challenges for engineers. Size matters, of course: the ever-decreasing real estate in portable electronics and the quest for ultra-thin TVs present the most obvious design hurdles.
However, as electricity prices continue to rise with no end in sight, consumers and regulatory agencies alike are demanding improved energy efficiency in electronic products. Meeting these new energy challenges is especially important to those who have been tasked with overhauling power-hungry electronics like plasma TVs into greener applications.
Different U.S. states and energy-conscious industrialized nations have varying environmental regulations. But the efficiency standards most manufacturers want to meet are the Energy Star requirements.
At present, this means that power supply units (PSUs) must have at minimum 80% efficiency at various levels of the device’s rated output. At 100% of the device’s rated output, it must have a power factor of 0.9 or better.
Furthermore, the Energy Star requirements are increasing. Starting in July 2008, manufacturers must meet 82% efficiency at 20% and 100% of a PSU’s rated output and at least 85% efficiency at 50% of the rated output.
Meeting energy-efficiency challenges
Fortunately, the newest generations of resonant power controllers provide designers with energy-efficient solutions. ON Semiconductor (Phoenix, AZ) offers its NCP1396, a high-performance resonant mode controller with high- and low-side drivers. The controller bundles a 500-kHz voltage controller oscillator with a MOSFET driver for half-bridge applications of up to 600 V. This controller is intended for products such as LCD TVs and flat-panel computer displays as well as medical and industrial power supplies.
The NCP136 includes a variety of current protections for safety and offers a programmable skip cycle for low standby power consumption. Its LLC half-bridge converter reduces power loss by removing the electricity drains that typically happen when devices that rely on other topologies are turned on. The company estimates the device meets or exceeds 90% energy efficiency.
The L6599 power controller from STMictroelectronics (Lexington, MA) is intended for applications such as LCD monitors, plasma TVs, laptop computers, servers, and game boxes. Like the NCP1396, it combines a resonant converter control circuit and a 500-kHz voltage controller with a half-bridge driver and can handle power loads of up to 600 V. This controller enables engineers to employ simpler, smaller circuit designs because the controller features and all the driver circuits are integrated into a single package.
In addition to reducing electromagnetic interference, the L6599’s construction enables increased energy efficiency. The device consumes less than 30 mW, and its nonlinear soft-start limits voltage overshoots and stops inrush current. It also offers burst-mode operating to reduce switching frequencies and losses. Furthermore, if the device is used in systems that employ power factor correction, its dedicated output enables it to turn off the PFC preregulator during burst mode operations, which helps to eliminate parasitic power drains.
Fairchild Semiconductor’s Green FPS FSFR2100 half-bridge resonant power switch.
An efficient solution
The Green FPS FSFR2100 half-bridge resonant power switch from Fairchild Semiconductor (South Portland, ME) can be used in ac input power supplies from 70 W up to 1 kW. It is intended for use in telecommunications devices, LCD TVs and monitors, plasma displays, high-end audio amplifiers, desktop computers, servers, and laser printers. This integrated switch provides a “system-in-a-package” that bundles all the components needed for reliable, efficient resonant converters into a space-saving, heat- and energy-efficient 9-SIP package.
The FSFR2100 incorporates a pulse-frequency-modulation (PFM) controller with a high voltage gate driver circuit, two fast-recovery MOSFETs, soft-start, and burst operation.
The circuit protection features include overvoltage, overload, and overcurrent protections, plus internal thermal shutdown. It operates at up to 300 kHz and offers pulse skipping for programmable frequency limiting during light load conditions.
Fig. 1. Principle of zero voltage switching.
The FSFR2100 offers zero voltage switching (ZVS), which greatly reduces switching losses and heat buildup in MOSFETs and rectifiers. The switching frequency does not change much, no matter what the power load is (see Fig. 1 ). With ZVS, this FPS switch can even be used without a heat sink and handle up to 200 W; with a heat sink, it can handle 450 W.
In comparison with standard hard-switch converter designs, energy efficiency in the FSFR2100 is improved by 10%; in a 200W power supply this switch should be at least 94% efficient. When used in electronics such as plasma televisions, efficiency should reach 97%, exceeding Energy Star standards.
Another advantage of this ZVS technique is that switching noise is considerably reduced at least 5 dB compared to hard-switching techniques. Through its burst operation function, the FSFR2100 takes standby power consumption down below 1 W to easily achieve the industry’s 1 Watt Initiative. The switch also uses lead-free terminals and conforms to the European Union’s Directive on limiting the use of toxic materials.
Whether you’re designing laptop screens or plasma TVs, gaming consoles or wireless base stations, there are power switches and controllers on the market to help you make your products smaller, cooler, and greener than ever before. ■
Visit http://resonantpower.electronicproducts.com to see full coverage of power controllers. Fairchild Semiconductor is a global leader delivering energy-efficient power analog and power discrete solutions. Fairchild is The Power Franchise, providing leading-edge silicon and packaging technologies, manufacturing strength and system expertise for consumer, communications, industrial, portable, computing and automotive systems. An application-driven, solution-based semiconductor supplier, Fairchild provides online design tools and design centers worldwide as part of its comprehensive Global Power Resource. Please contact us on the web at www.fairchildsemi.com.
Visit http://resonantpower.electronicproducts.com to see full coverage of Power ControllersSponsored by Fairchild Semiconductor • www.fairchildsemi.com
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