Electronic Design

Power: Overview

Greater Complexity Shapes Power Designs

Growing demands for current in advanced system designs continues to drive power-supply development. Much of the progress in this direction can be traced to gains made in power-conversion technology, thanks in large part to improvements in power ICs and power semiconductors. Better magnetics, capacitors, cooling devices, and packaging must also be credited. In general, these components contribute to enhancing power-supply performance by increasing power-conversion efficiency, or by removing more heat from the components, or through a combination of both. Migrating to lower voltages shapes the development of these components, but it also creates serious design challenges. One such challenge involves trying to power next-generation microprocessors. The core voltage levels are low (1 V or less), peak current demands are high (100 A or more), and voltage regulation tolerances are tight, even in the face of fast load transients and dynamically changing supply levels. In response to these requirements, power semiconductor companies are crafting chip-based solutions for complex, multiphase power converters necessary to meet these requirements.

These solutions will include repartitioning of control functions to create scalable multiphase designs along with improvements in current-sensing techniques and voltage references. Power MOSFETs are also being enhanced through silicon, packaging, and application-oriented design.

Beyond these developments, more-radical approaches, such as digital control techniques, should put a new spin on multiphase power designs. One digital approach promises more sophisticated control schemes that will offer noise immunity, flexibility, and configurability.

While these advances are significant, other factors also shape power technology, especially at the system level. One factor is the proliferation of supply voltages. While new chips are pushing supply voltages down, many of the legacy devices still need the higher voltage levels. Therefore, pc boards require more and more voltages. This trend influences power design at the system and component levels.

One effect is the continued migration from centralized power schemes to distributed power architectures to avoid the losses associated with busing high currents over long interconnect paths. A twist on the traditional approach to distributed power—the use of an intermediate voltage bus—has triggered the development of point-of-load (POL) modules as well as IC-based solutions for embedded POL designs. It has even created a new category of isolated, unregulated power modules known as bus converters.

The power converters used in distributed power schemes—both the modules and the IC-based solutions—keep improving in terms of their electrical performance, ease of use, and cost. As a result, the challenge for system designers may now be how to address system-level power-management issues.

Other system-level concerns are also leaving their mark on power-supply and power-system design. One is the demand for "high nines" reliability, which drives development of UPS systems. A coming challenge may be supplying the unprecedented power levels that could be required from blade-server systems.

A related development is the emergence of power-over-LAN as a means for extending UPS-style reliability to peripherals across the network. Power-supply vendors are now working to deliver supplies that meet the electrical requirements spelled out in the IEEE 802.3af power-over-LAN standard.

Meanwhile, requirements for portable power management continue to push the development of power-conversion components and power sources. For semiconductor vendors, advances in LDOs and other power components tailored to specific portable applications will help to maximize battery life in light of increasing demands for power. Battery manufacturers are also doing their part to come up with better Li-ion batteries, including the newer Li-polymer types. With the Li-polymer batteries nearing the mainstream, more applications stand to benefit from their thin form factors and inherent safety advantages.

Standard Li-ion batteries may be closing in on the performance limits of existing chemistries. However, the advent of nickel-based electrode systems and other changes in chemistry should continue to boost cell performance in the near term. Hopes for the next big breakthrough in power-source performance are being pinned on direct-methanol fuel cells. But with so many of these devices still in the prototype stage, it's unclear just when fuel cells will begin to impact portable designs.

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