greenpowerZONE Products for the week of May 7, 2007
ON Semiconductor Says....
GreenPoint ATX Reference Design Exceeds New EnergyStar, Efficiency Standards For Desktop PCs
Latest open reference design for 300 W ATX power supplies reduces losses by 50% over existing solutions
ON Semiconductor has unveiled the industry's first open ATX reference design that meets the new ENERGY STAR performance requirements for ATX power supplies used in desktop PCs scheduled to take effect this July. The new reference design delivers efficiency that exceeds the ENERGY STAR requirements under all specified load conditions, and provides a blueprint for power supply manufacturers to bring highly efficient power supplies to market with readily available, cost-effective technology.
"ON Semiconductor has clearly demonstrated that it is both technologically possible and financially feasible to deploy highly efficient ATX power supplies to the market today," said Andrew Fanara, director of ENERGY STAR Product Development at the U.S Environmental Protection Agency. "The availability of this open reference design prior to the effective date of the new ENERGY STAR requirements for ATX power supplies has very positive implications for energy savings in the desktop PC market."
ON Semiconductor's reference design achieves full-load efficiency of 86.5 percent at high-line and 82.5 percent efficiency at 20 percent of load and low-line. This reduces power losses by approximately 50 percent, compared to the typical power supplies on the market today that average 70 percent power efficiency. Additionally, ON Semiconductor's ATX reference design meets IEC61000-3-2 power factor requirements.
"ON Semiconductor's 300 W GreenPoint ATX reference design demonstrates our unwavering commitment to deliver innovative, turn-key power solutions for extremely efficient power supplies," said Andy Williams, senior vice president and general manager of ON Semiconductor's Automotive and Power Regulation Group. "We worked closely with worldwide regulatory organizations and our customers to develop this cost-effective ENERGY STAR compliant power supply solution. ON Semiconductor will continue to introduce additional GreenPoint power solutions addressing the global need for power efficiency in both active and standby modes."
 The ATX Reference Design
The reference design addresses all functional blocks of the ATX power supply, including power factor correction, switch-mode power supply control and regulation, post regulation and standby power. The design utilizes several of ON Semiconductor's newest power management devices and draws from its leading discrete component portfolio to achieve superior efficiency performance.
Key products in the reference design include:
- NCP1653: This compact continuous conduction mode (CCM) power factor correction (PFC) controller makes the choice of incorporating a PFC front-end into an ATX design easy, by reducing part count and providing a robust, cost-effective front-end without range switches.
- NCP4330: This synchronous post-regulator replaces the mag-amp to provide higher efficiency in the output section of the ATX power supply.
- NCP1562: This active-clamp pulse width modulation (PWM) voltage-mode controller has a ±5% duty cycle limit with a soft-stop to prevent the typical oscillations in the forward active-clamp topology. The device has a dual-mode over-current protection circuit that handles momentary and continuous over-current conditions differently.
- NCP1027: This high-voltage switcher includes a power MOSFET together with a startup current source, all directly connected to the bulk capacitor. To prevent lethal runaway in low input voltage conditions, an adjustable brown-out circuitry blocks the activity until sufficient input level is reached.
- NCP4330: This synchronous post-regulator replaces the mag-amp to provide higher efficiency in the output section of the ATX power supply.
- MSR860: This 8 amp (A), 600 V power rectifier features SWITCHMODE soft recovery.
EN-Genius Says...
Although my colleague (and resident power guru) Paul had some choice words to say about the vagueness of the so-called schematic that accompanies the press release for ON's EnergyStar-compliant ATX power supply reference design (see his Editorial, Circuit Pants on Fire), the claims it made were intriguing enough to warrant a deep dive into its architecture. During my briefing, the folks at ON stowed the simplified promotional block diagram (above) and used the schematics in their documentation package to point out several of the key features that contribute to its overall performance. What I found is a design that, while not perfect, is very market-appropriate and cost-effective, as well as remarkably energy frugal.
 I still might quibble with the creative specsmanship that led ON to claim a 50% efficiency advantage over its competitors, but I could not argue that this design sets an excellent precedent by actually exceeding current requirements of the EnergyStar and 80Plus eco-branding programs in several important ways. That's why the thing that stands out when you first look at the reference design's detailed documentation package is its extremely flat efficiency curve (see Fig. 1.). Although switch-mode power supplies have matured considerably since I last worked with them two-plus decades ago, none of the improvements I've seen in that time included a design that delivers over 80% efficiency from 20% to 100% of its full rated load. This wide efficiency band is important since ATX-style power supplies are used in applications that can range from a sub-100 W econo-PC to an up-armored, multi-processor gaming unit with multiple graphics cards that pushes the upper limits of the supply's 300 W capacity.
 Similar care has been taken to ensure maximum efficiency from the supply's 15 W standby circuit (see Fig. 2) which may be asked to run DVD players or other peripherals while the rest of the box hibernates. As we'll see, this performance is not the result of a single technical breakthrough but a series of improvements sprinkled across the different sections of the design and careful attention to the overall architecture.
This is ON's 2nd-generation 80 Plus-compliant ATX supply reference design that allows manufacturers to enjoy several dollars in subsidies provided by a consortium of energy-aware power companies (see my Fall 2005 review for details on how this works). The new design improves on the original in several important ways that give it even better efficiency, cut system cost, and make it easier to manufacture in high volumes.
Like many modern switchers, the power factor correction section employs continuous conduction mode for minimum losses but the main dc-dc controller breaks with conventional architectures by employing what ON calls a forward active clamping circuit. The resonant circuit in the clamp allows near-zero volt switching for lowest parasitic loss within the power transistor -- even at light loads. The standby section delivers standard ATX standby functionality (5 V@3 A) using ON's new NCP 1027 which sports an integrated power MOSFET (lower BOM and assembly costs) and still manages to deliver roughly 80% efficiency.
The synchronous rectification and post regulator section cranks out the standard 12 V and 5 V feeds with a simpler switching scheme used for the small amount of -12 V needed in a typical computer system. Both 12 V sources are derived directly, while the 3.3 V is derived from a tap in the 5 V winding. Paul voiced some skepticism about the 3.3 V switched post-regulation stage which replaces the traditional magnetic amplifier (which uses the sharp saturation curve of a specialized core to do the regulation). ON explained that they moved away from mag amps because they replaced the section's traditional Schottky diodes with more efficient MOSFETs which don't work well in mag amp circuits. They also said that going to the new post-regulator scheme frees up designers from the relatively small number of magnetics vendors which provide mag amp components.
ON was a bit guarded about details of the supervisory section that monitors the supply for over/under-voltage conditions because the current design uses a popular 3rd-party commercial IC . While I could not get any specifics, ON assured me that they have an-in-house supervisory IC in the works that they expect to be ready by early Q3 2007.
But as innovative and efficient as their design might be, it won't go anywhere unless it is accepted by the risk-averse, penny-wise offshore manufacturers who build most of the world's PC power supplies. That's why ON's 2nd-gen design team has spent lots of time consulting with a major Taiwanese ODM to make sure all the components called out in the design are commonly used, inexpensive, and easy to obtain. It's also interesting to note that ON says that many of the passive component values listed in their detailed BOM can be tweaked to match the parts a manufacturer already stocks, or at least adjusted to reduce the number of items required to be ordered, stocked and inventoried in the supply chain.
In a similar vein, the supply's main board is implemented as a low-cost single-sided PCB with only thee small multi-layer daughter cards needed to mount fine pitch elements like the post-regulator, power factor correction, and switch mode controller. The plug-in arrangement also lets manufacturers update their designs quickly as their requirements change or better components become available.
The result of ON's update of its reference design is a product that strikes a smart balance between the environmental imperative for extreme energy efficiency and the sometimes unpleasant realities of commercial electronics manufacturing. I'll look forward to seeing whether ON applies the lessons learned here to other markets such as power supplies for set top boxes, printers, televisions, and other high-volume consumer gear.
ON Semiconductor has a complete documentation package for the ATX reference design, including description, schematics, bill-of-materials, Gerber files and evaluation guidelines. The documentation package is available here, as are links to relevant industry information and other supporting information.
- Offered in Pb-free SOIC-8 and PDIP-8, the NCP1653 is priced at $0.80 in 2500-piece lots. Data Sheet
- Offered in Pb-free TSSOP-16 and SOIC-16, the NCP1562 is priced at $1.60 in 2500-piece lots. Data Sheet
- Offered in Pb-free PDIP-8, the NCP1027 is priced at $0.97 in 1000-piece lots. Data Sheet
- Offered in Pb-free SOIC-8, the NCP4330 is priced at $0.60 in 2500-piece lots. Data Sheet
- Offered in Pb-free SOIC-8, the NCP4330 is priced at $0.60 in 2500-piece lots. Data Sheet
- Offered in Pb-free TO-220, the MSR860 is priced at $1.07 in 50-piece lots. Data Sheet
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