Microsite Turns Spotlight on Digital Power
For engineers interested in the emerging area of digital power-supply design, a new microsite offers a unique source of design information, product and technology news, and analysis. The Spotlight On Digital Power — an extension of the Power Electronics Technology (PET) website — features an extensive collection of articles on all aspects of digital power management and control as they relate to power-supply and power-system design. In addition to the many articles gleaned from the pages of PET magazine and the PETech Times newsletter, this site also offers exclusive features.
One such feature, Guest Commentary, offers an industry perspective on the technology or business of digital power. In the first of these commentaries, Reno Rossetti, director of the Analog Product Group Strategy at Fairchild Semiconductor (South Portland, Maine), responds to some of the critics of digital power design, explaining how and why “Digital Power Can Flourish in an Analog World.”
Another exclusive to the microsite is the Digital Power Q&A, where industry experts weigh in on issues of the day and where readers get their turn to respond. To kick off the discussion, we asked representatives of the power-supply industry: “Is the power design community ready to switch from analog PWM controllers to digital PWM controllers?” Bob White, staff engineer at Artesyn Technologies (Boca Raton, Fla.), and Mark Wells, director of marketing at Power-One (Camarillo, Calif.), share their insights on this issue. This feature will be updated regularly with new questions posed to different members of the industry.
“With the recent arrival of new digital power components and design tools, many seasoned analog power-supply designers may be interested in tackling a digital power design,” says David Morrison, editor of PET. “Our new microsite will help these engineers come up to speed quickly on the technology, learn about the many product options, read related industry news and hear a range of opinions on the issues shaping the digital power field.”
In addition to the application-oriented digital power design articles, the microsite will offer access to vendor white papers as well as conference papers on digital power topics.
Switcher Delivers More Than 200 W in 3-in. × 5-in. Footprint
By applying several proven power-supply design techniques, XP Power has created a single-output ac-dc power supply that delivers 212 W in the popular 3-in. × 5-in. footprint, achieving a power density of 10.55 W/in3. Designed for communications applications in the 1U format, the EMA212 is the first 3-in. × 5-in. switcher to deliver more than 200 W across the full universal ac input range, claims XP Power.
The supply operates with a typical efficiency of 91% at 50% load with 48-V or 12-V output and a 110-Vac input. Because of its high efficiency, the EMA212 needs only 12 CFM (about 200 LFM) of airflow for full power operation at up to 50°C ambient and will operate at up to 70°C ambient with derating. In addition to the main 12-V or 48-V output, each power supply has a 5-V, 100-mA standby output and a 12-V, 1-A output for powering a fan. The unit incorporates a fully featured signal set including ac fail/dc OK, active power factor correction (PFC), remote on/off and active current sharing.
Several complementary design techniques were combined to achieve the EMA212's performance. The size of the input filter was reduced with a two-stage design using miniature, high-permeability cores. Stacked mounting of the cores minimizes the printed circuit board area needed and maximizes cooling effectiveness. In addition, the PFC circuit uses a silicon carbide (SiC) diode from Cree to gain a further 1% improvement in efficiency over silicon diode and snubber circuit combinations. A stepped-gap inductor operating in continuous mode reduces peak switching current and minimizes filter requirements.
Meanwhile, the use of a resonant zero-current-switching (ZCS) topology for the main converter circuit virtually eliminates switching losses. Switching occurs at the zero-current point from 0% to 100% load. Furthermore, a 100-kHz switching frequency enables the use of small magnetic components without compromising efficiency. Another innovation in the main converter is the use of a ceramic substrate in place of a metal heatsink, which saves space.
The substrate is a standard ceramic tile from CoorsTek (Golden, Colo.) and has much lower thermal conductivity than aluminum. However, the dissipation of the TO-220-packaged MOSFETs used in the supply is kept low, and the ceramic substrate provides just enough heatsinking to allow full power to be obtained from the MOSFETs. Ceramic substrates are beneficial because they eliminate the EMC and noise issues associated with metal heatsinks. The same cooling technique is used for the output rectifiers. Here, the adoption of synchronous rectification eliminates nearly all switching losses.
To implement PFC, the company applies International Rectifier's one-cycle control (OCC) circuit, rather than an average current control mode operating over several cycles. This OCC technique eliminates six passive components, saves pc board space and reduces cost.
The EMA212 also provides overcurrent, overvoltage and short-circuit protection. The power supply is sampling now with production quantities available starting in September.
The units are priced at $82 each for 1000 pieces. For more information, see www.xppower.com.