Electronic Design

Solving The Standby Power Challenge

Many electronic devices operate in low-power, functional, and nonfunctional states, ready for an externally activated signal. This is called the standby mode. These devices are always on, dissipating power even when the output power or load is zero. Designers need to be concerned about how this wasted power affects the nation and the world.

Standby power typically accounts for about 10% of all residential power, or 20 to 60 W per household in developed countries. Desktop PCs, laptops, TVs, VCRs, DVDs, and set-top boxes all use it. Lawrence Berkeley National Laboratories says that approximately 7% of U.S. residential consumption, or 5 billion W, goes to standby power. This equals the output of 25 2-MW, fossil-fueled power plants. In general, statistics for standby power use and the resultant waste products are relatively consistent across the developed world.

The International Energy Agency has hosted several worldwide summits to discuss and initiate a plan to reduce standby emissions. In 1999, it pioneered and endorsed the "Global 1Watt" program, recommending that any device operating in standby mode consume less than 1 W of input power. In July 2001, President George W. Bush issued a White House Executive Order endorsing Global 1Watt, encouraging government agencies to buy equipment that complies with the standard. He also recommended that the EPA's Energy Star labeling scheme include the 1W initiative.

Early on, the European Union recognized the standby power problem and began discussions with TV and VCR manufacturers in 1995 to reduce standby dissipation. The EU opted for a voluntary agreement, and key global electronics players signed a European Community Code of Conduct, which effectively embodied the 1W initiative by 2001 and implemented tighter standby limits, scaled to the output power for 2003-2005. The EU proposed that the manufacturers indicate standby performance on the product ratings label, devolving the purchase decision to the final customer based on energy savings.

The Australian Greenhouse Office and the Australia & New Zealand Minerals and Energy Standing Committee of Officials have been vital in the Global 1W scheme, signing reciprocal Energy Star agreements. Japan has largely endorsed Global 1W, with some makers floating targets of 10 mW. The cost of implementation and the availability of technology, particularly above 30 W of output power, provides technical and commercial challenges.

Advances in semiconductor IC processes and increased functionality have helped power-supply manufacturers meet these proposals. High-voltage semiconductor processes let power-supply ICs start directly from the rectified ac bulk, eliminating the power dissipated in the startup resistors normally used to attenuate the high-voltage bulk to the low-voltage IC.

Techniques for reducing the controller's switching frequency are being applied to reduce power-semiconductor and magnetic switching losses at low output or standby power. Certain functions, like the power-factor-correction circuit, can be turned off during standby to save energy. This requires careful attention to sequencing and topology selection. Improved low-loss magnetic materials and low-gate-charge FET switches also tend to reduce losses.

Recent measurements over a range of Astec power supplies indicate that the requirements of the Global 1W standard and the European Code of Conduct can be satisfied across a relatively wide 2- to 150-W power range. In the sub-5-W range, applicable to mobile chargers, standby power levels as low as 300 mW can be achieved. As processing power increases, power supplies above 100 W will become important for notebooks and LCD PCs. But even in this range, existing power supplies can comply with the proposed initiatives.

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