Electronic Design

Power: Power Supplies

System Needs Will Demand Greater Attention To Power
In the past, power-supply selection was often treated as an afterthought in system design. But that approach is becoming increasingly dangerous in this era of short product development cycles and high performance. In so many applications, the electrical performance, integration, and reliability of the system depend upon the power supply's capabilities. Designers who consider the power supply early in their system design processes are better able to take advantage of the increasing power density, efficiency, and flexibility of new power-supply products.


Power-supply and system-en-closure design will continue to converge as designers seek greater power and current density. This trend reflects a need to consider the system's power-distribution and cooling requirements when designing the power supply. In essence, power-supply packaging has become inextricably linked with system-level packaging because of the space limitations associated with telecom and datacom applications.


Software control of power supplies is coming. At least one vendor, Lambda (www.lambdapower.com), is planning to introduce a software-controllable and readable modular power supply. The software will not only allow adjustment of output voltages, but also permit troubleshooting of prototype systems. In general, there will be a strong demand for power supplies equipped with the I2C interface, which will provide a means of monitoring status of variables such as current, voltage, and temperature in real time.


Greater customization beckons. Power-supply manufacturers will improve the configurability of their designs to the point where standard off-the-shelf units will offer performance and features that were in the past attainable only with custom products. This trend will yield more options for output voltages, number of outputs, ability to parallel units, interconnect, and packaging, and features such as power-factor correction and electromagnetic interference (EMI) filtering.


Power density of ac-dc power supplies will rise still more. One company, Delta Electronics (www.deltaww.com), plans to deliver units with power densities ranging from 2 to 6 W/in.3 These will include ac-dc power supplies with 5 outputs at 3.3 V or higher, power output ranging from 30 W to 3 kW, universal ac input with power-factor correction, package heights varying between 1U and 4U, and efficiency percentages ranging from the high 60s to the low 80s. The 6 W/in.3 represents state-of-the-art performance and amounts to a 20% improvement over what the company achieves currently in this category. For single- and dual-output supplies, Delta expects performance to increase from 10 to 11 W/in.3 this year. These devices include those with either 12- or 48-V outputs and percentage efficiencies in the low to high 80s.

See associated timeline.

Demand for extended backup power grows. One factor in the UPS arena will be the system requirements for "always on" operation. In part, this means longer run times for backup power sources. But it's unclear how system designers will ultimately achieve that.

The ability to scale UPS runtime independently of power output, as APC (www.apcc.com) has done with its Symmetra line, is one approach that may be feasible for systems with several kilovolt-amps of backup power. Yet as power levels rise, this approach may become too costly for many applications, given the number of lead-acid batteries needed. In fact, because of the great battery requirements for systems over 100 kVA, the trend may actually be to decrease battery runtime in these systems. In such cases, the battery-based UPS may just be used to switch over power to a generator.


The search for new backup power sources goes on. Unfortunately for most electronic systems, using backup generators as a secondary power source presents difficulties. Diesel generators produce exhaust and noise, as well as require frequent maintenance, special permits, and hazardous fuel storage. Microturbines are emerging as a generator alternative because they extend runtime while reducing emissions and maintenance versus diesel generators. At some point, other battery chemistries such as NiCd, NiMH, and Li-ion may provide the means for extending UPS runtime, as they have in low-power portable products. For the near term, they are by and large too expensive. There is hope in the long run that fuel cells such as the zinc-air technology under development at Metallic Power (www.metallicpower.com) may answer demands for long-duration backup, but probably not in 2002. At the moment, other fuel-cell possibilities seem to be either premature or too costly.


This year's Applied Power Electronics Conference (APEC 2002), which will run March 10 through March 14 at the Adam's Mark Hotel in Dallas, will inform attendees of the latest technical developments and issues in power design. Seminars, paper sessions, exhibits, and rap sessions will address a broad range of topics, including:

  • Powering high-performance next-generation and beyond microprocessors
  • Designing the ac-interface for IEC1000-3-2 and the research to raise the efficiency of power-factor-corrected ac-dc rectifiers
  • Tools and analysis techniques for magnetics design
  • Advanced concepts in industrial drives, such as sensorless control and novel control algorithms
  • Advances in synchronous rectified dc-dc converters
  • Digital control in low-cost ac-dc rectifiers and voltage-regulator modules
  • Packaging, thermal management, and reliability for high-density power conversion beyond the 100-W/in.3 level.

Embedding of passive components in pc boards will become more prevalent. Burying of passives will increase packaging density, reliability, and performance. In particular, buried capacitors will help designers compensate for parasitics and attenuate power-supply switching noise.


Dual-output supplies, supplies with two main outputs rather than simply one main output and an auxiliary, will continue to offer designers needed flexibility. For example, if a supply features high-current outputs at both 5 and 3.3 V, it can be used in applications with high current demands at either voltage. This capability also enables designers to easily migrate their designs from one voltage to another over successive product generations. As ASICs migrate to lower voltages, dual-output capability should become increasingly useful.


The use of IGBT modules will reduce the size and cost of uninterruptible power supplies. In general, power-supply designers are employing surface-mount components whenever possible to reduce space requirements. But with power components, this is not always possible. For companies like MGE UPS Systems (www.mgeups.com), replacement of discrete IGBTs with IGBT modules such as the "sixpack" is enabling continued size reduction for the UPS. This modular approach permits the heatsink to be reduced by a factor of four or five while reducing filtering requirements. As next-generation UPS designs migrate from discrete IGBTs to modules, MGE UPS Systems expects to see space savings of 20% to 30% and cost reductions of 10% to 15%. But because the IGBT modules concentrate the heat dissipation in a smaller space, cooling becomes more challenging and may even require liquid cooling.

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