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Initiatives to manage power proliferate

Posted: 16 Aug 2004 ?? ?Print Version ?Bookmark and Share

Keywords:power management? power? crm? conservation? acpi?

Computing, communications and consumer products are fueling the race toward more integrated functions in smaller form factors, and consequently, escalating the rise in power density and power dissipation. A number of power-management protocols and initiatives have resulted, aimed at efficiently converting power from the source to the load.

Power management, often defined by the amount of heat that can be safely disposed of by the appliance, is evolving into energy management, driven by concerns for energy conservation and environmental protection. Given the importance of power and its management, it is no surprise that there are numerous initiatives and protocols underway to address this issue.

At the highest level of power-management techniques is advanced configuration and power interface (ACPI), an open industry specification co-developed by Compaq, Intel, Microsoft, Phoenix and Toshiba. ACPI establishes industry-standard interfaces for OS-directed configurations and for power management on laptops, desktops and servers.

ACPI power ICs take the available voltages from the silver box or AC adapter and, under specific OS commands applied to the power chip via logic inputs, translate them into useful system voltages on the motherboard. This specification allows new power-management technologies to evolve independently in OS and hardware, while ensuring they continue to work together.

Most challenging load

Efficient powering of a CPU - the most challenging load on a motherboard--is done with special voltage regulators often described as voltage regulator modules (VRMs). These regulators include techniques such as voltage positioning or dynamic voltage adjustment of the output, via a DAC, to accommodate transitions to and from low-power modes. Such techniques, first applied to desktop CPUs, have migrated to notebooks and are becoming popular in ultraportable devices.

A number of specifications, some proprietary, address those challenges. VRM specifications for desktop computing detail the architectures, external components and protocols to apply in powering every new generation of CPUs.

Notebooks employ a set of aggressive power-management techniques aimed at maximizing performance with the minimum expenditure of energy. Such techniques are similar to those discussed for VRMs but go much further. In addition to voltage positioning, here are additional power-management techniques for notebooks:

??? Light-load operation - At light load, voltage regulator switching losses become dominant over ohmic losses. Hence, the switching-regulator clock frequency of operation is scaled down at light load. This is done either automatically, commuting to light-load mode below a set current threshold, or under microcontrol, using a digital input toggling between the two modes of operation.

??? Clock speed on demand - One of the most effective ways to contain power in notebook computers is to manage the CPU clock speed and supply voltage, since power dissipation goes with the square of the voltage and in proportion to the frequency. Different CPU manufacturers offer varying flavors of this technique. The bottom line is that for demanding applications, such as playing a movie from a hard disk drive, the CPU gets maximum clock speed and highest supply voltage, thereby yielding maximum power. On the other hand, for light tasks, such as typing a memo, the power is reduced considerably.

The conversion and regulation of power from the wall traditionally has focused on satisfying safety requirements. Recently, however, power management has become important in this area as well.

Power factor correction regulation is concerned with the efficient drawing of power from the wall, as opposed to minimizing power dissipation inside the gadget. Optimum power delivery from the AC line occurs when the electric load draws current that is in phase with the input voltage and when such a current is undistorted.

To this end, IEC 6100-2-3 is the European standard specifying the harmonic limits of various equipment classes.

For example, all PCs drawing more than 75W must have harmonics at or below a specified profile. With modern desktop power supply units drawing from 140W to 300W, this means that all PCs shipped to Europe must comply. When it comes to compliance, the rest of the world is following Europe's lead, albeit at its own pace.

The allowance grows stricter for higher harmonics. However, these harmonics also have less energy content and are easier to filter. According to the specification, the allowed harmonic current does max out above 600W, making it more challenging to achieve compliance at higher power.

Green power refers to sustainable energy systems based on renewable energy, such as power from the sun, wind, plants and moving water. With respect to power conversion, green power loosely refers to a set of initiatives aimed at reducing power consumption of electrical appliances while in standby mode.

Operational power

Future initiatives will address operational power reduction. Some major initiatives include:

??? Blue Angel - In 1977 Germany became the first country in the world to use an eco label when the federal minister of the interior and the ministers of the environment of the Federal States first introduced the Blue Angel label to promote environmentally-compatible products.

??? Energy Star - The Energy Star label first appeared in 1993 on PC. To bear the label, a product must operate significantly more efficiently than its counterparts, while maintaining or improving performance.

??? 1W initiative - The International Energy Agency created the 1-Watt initiative to reduce standby power losses to below 1W. The initiative was launched in 1997 and adopted by Australia first.

Recently, the focus is shifting from standby to operating-power savings. Initiatives like Efficiency Challenge 2004, a power supply design competition sponsored by the Environmental Protection Agency's Energy Star program and the California Energy Commission, will likely push the limits even further.

- Reno Rossetti

Director of Corporate Strategy

Computing and Ultraportables, Fairchild Semiconductor Int.

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