One Million Dollar Prize for Next Generation of Power Inverters

Google recently announced their so-called Little Box Challenge, a $1 million prize to develop the next generation of power inverters. If you want to know what power inverter is, here is the basics. Unfortunately, they did not provide any technical details on what exactly they are looking for. The referred website http://www.littleboxchallenge.com/ as of today provides zero useful info either. Hopefully, they will clarify the competition shortly.

Higher Distribution Voltage for Server Efficiency Increase

Several years ago Google suggested an open standard for desktop PC power supplies with a single 12V rail instead of multiple rails. The point was the higher buss voltage the higher overall PC PSU efficiency.

This year Google power designers are going to present at DesignCon 2013 their strategies for reducing energy losses in servers, including DC-DC regulator architectures as well as higher voltage distribution. Google apparently is going to make a case that higher distribution voltage levels improve overall conversion efficiency. Obviously, raising the buss voltage will lower conduction losses. On the other hand, switching losses in downstream DC-DC regulators will increase. In addition to this, you will need to use higher voltage MOSFETs whose characteristics generally degrade with their rated voltage. That's why it will be interesting to see their experimental results and  conclusions on optimal distribution level.

New Proposed Efficiency Standards for Battery Chargers and External Power Supplies

U.S. Department of Energy recently issued Battery Chargers and External Power Supply (BCEPS) Notice of Proposed Rule. DOE proposes amended efficiency standards for Class A external power supplies (EPSs) and new standards for non-Class A EPSs and battery chargers. The proposed standards set the minimum average efficiency in active mode and the maximum power consumption in no-load mode as a function of the nameplate output power. The greatest challenge for SMPS power supply designers in my view will be the proposed limit of maximum power in no-load mode. For EPS below 50 watt it will be <0.1 watt. Since a power supply has to be able to “wake up” when connected to a load, it needs to keep active certain control circuit. Keeping a consumption of an off-line bias supply below 0.1 W will be a real challenge.

The U.S. Department of Energy (DOE) will hold a public meeting on May 2, 2012 to discuss the analyses presented and issues identified in the Notice of Proposed Rulemaking and Technical Support Document. These proposed standards, if adopted, would apply to all applicable external power supplies manufactured in, or imported into, the United States on or after July 1, 2013.

At abote the same time, U.S. Customs and Border Protection (CBP) issued a notice of proposed rulemaking about Consumer Products and Industrial Equipment Non compliant with applicable Energy Conservation or Labeling Standards. CBP will refuse admission into the customs territory of the United States to consumer products and industrial equipment deemed non compliant with the Energy Policy and Conservation Act of 1975 (EPCA).

I feel our government is just one step short of stopping anyone at the border for carrying a cell phone with non-efficiency-compliant charger.

Converting Waste Heat to Electricity

A company called Nextreme Thermal Solutions, based in Durham, N.C developed a thermoelectric generator (eTEG) that converts heat directly to low-level electrical power. Their technology uses the Seebeck Effect in which the temperature difference between two metals creates an electrical potential difference. Their generator uses Linear Technology LTC 3108 ultralow voltage step-up converter and power manager chip and can produce voltages up to 5V at power level up to 1 mW on a temperature difference of 15 to 20°K (the temperature difference in Kelvin is the same as in Celsius). Higher temperature gradients will result in higher power. Such devices can be used to feed micropower wireless and battery-free sensors. Unfortunately, the eTEG power levels are not sufficient to increase efficiency of power supplies by recycling heat energy from heatsinks. Also unfortunately, the prices starting at about $500 make this technology cost-prohibitive for regular consumers and hobbyists. By the way, the thermoelectric effect has been known for almost two centuries since Thomas Johann Seebeck discovered that electrical current flows between two dissimilar metals which have different temperatures.

Energy Efficient TV with 0 Watt Standby Mode

Toshiba Corp is reportedly releasing a 32 inch (visual size) LCD TV model "Regza 32BE3" equipped with its so-called "Eco Chip." The Eco Chip consumption current is said to be as low as about 95μA. This chip is used to detect ON signals from the remote control after the TV is turned off. It cuts off the AC power entirely through a relay as if you an unplugged TV. As the result, the power consumption in standby mode is 0 watt. The relay and the sensor that receive signals from the remote are powered by a large storage capacitor. Unfortunately, the report does not state the size of this capacitor and what happens when you leave the TV off for a long time. I guess either the chip needs to turn on the relay and re-activate standby bias supply before the cap is discharged too low, or you would need to turn on the TV by hand if the cap is discharged. Also they did not state power consumtpion or internal power supply efficiency in active mode (I wonder if they use bridgeless PFC front end?) In any case, such a "zero power standby" circuit is cute, but it is nothing more than a marketing gimmick. Obviously, you need to charge the storage cap during on-mode of the TV set. Whatever energy you save in 0W standby mode you need to spend to put this energy into this cap.

More Troubles with Energy Efficient Bulbs

U.S. Consumer Product Safety Commission just announced a voluntary recall of LED night lights imported from China by Corvest Acquisition Inc. It was reported these LED lights can overheat, smolder, and melt which may cause burns to consumers. The affected part has model number SBD01 stamped on the back of the plastic base.

CFL Bulbs: Potential Mercury Danger

The U.S. Environmental Protection Agency (EPA) recently announced that they “improved” its guidance on how to clean up a broken compact fluorescent lamp (CFL). Included with the guidance is a new consumer brochure with CFL recycling and cleanup tips. Why is it you may ask, EPA pays attention on broken bulbs? They don’t tell you how to clean up a broken laptop or an ipod, do they? Well, as most of us know, CFLs contain mercury sealed within the glass tubing, an average of 5 milligrams. When a fluorescent lamp breaks, mercury vapor is released, which may pose health risks. EU’s Scientific Committee on Health and Environmental Risks asserted that when you are exposed to a broken bulb, there is a danger that “long-term toxicological limit values may be exceeded up to 6,000 times”. All this raises a number of questions:
· Why is it instead of just banning CFLs, EPA explicitly encourages Americans to use them?
· How come we don’t read on the CFL label something like this: “This product contains substances known to the state of California as causing kidney and brain damage”?
· Is not ROHS directive bans products containing lead and mercury in amounts exceeding 0.1 % in homogeneous materials? After all, in electronic equipment these elements present health threat only if you have a habit of chewing printed circuit boards, but releasing mercury vapor in CFL by accidentally (or intentionally) breaking may be a real threat.

A simple answer is: a CFL is more energy efficient than incandescent bulbs, and therefore it must be a politically correct health hazard. Probably for the same reason RoHS Directive conveniently exempts CFL from their requirements and allows up to 5 mg of mercury per lamp. And to add insult to the injury, the US government is phasing in between 2012 and 2014 new efficiency standards for lighting, which would preclude sale of most traditional incandescent bulbs (see Energy Independence And Security Act Of 2007 ). So, soon, we may not have a choice. European Union and Australia have already started to phase incandescents out in 2009. I guess, I am going to stock up on incandescents until we’ll be able to buy screw-in LED lamps at a reasonable cost. Of course, their "reasonable cost" will still be 10-20 times more than that of today's regular bulbs. Indeed, aside from high-intensity LEDs, they will have to include a small power circuit with power factor correction (PFC), but… we should not worry about it—the government knows what’s better for us.

Electricity Rates May Go Up Soon Due to New EPA Regulations

Last week, the U.S. Environmental Protection Agency (EPA) issued its plan for establishing new greenhouse gas (GHG) pollution standards. EPA Administrator Lisa Jackson said: “We are following through on our commitment to proceed in a measured and careful way to reduce GHG pollution that threatens the health and welfare of Americans, and contributes to climate change.”

Here is a little history. Last summer, the US House of Representatives narrowly passed the 1,000+ page American Clean Energy and Security Act of 2009, called the Cap-and-Trade bill. This bill particularly mandates a 17% cut in greenhouse gas emissions by 2020, puts a price on carbon dioxide emissions, requires that at least 20% of electricity comes from renewable sources, and mandates increased energy efficiency.

Basically, the government tried to "cap" the amount of carbon dioxide (CO2) and other so-called "greenhouse gases" that can be emitted nationally. Companies that emit such gases would be issued emission permits and would have to pay for these allowances every year. This of course would cause energy prices to rise, since the utilities and other companies would have to pay for emission permits and at the same time spend large amounts of money to change their technology. Does anyone have any doubts these extra costs will be passed on to the consumers? Luckily for us, the consumers, the Cap-and-Trade bill stalled in Senate. So now, having failed to impose their plan via Congress, the administration is moving unilaterally to develop new standards over the next year.
Note that CO2 is not declared a pollutant or health threat in itself, because it is not. Rather, its increase is said to have an insulating effect in the atmosphere and cause global warming. Most climate scientists support such a notion, although there are those who are skeptical about it. For example, Professor of Meteorology at the Massachusetts Institute of Technology Richard S. Lindzen asserts in his article titled "Global Warming: The Origin and Nature of the Alleged Scientific Consensus", “there is no substantive basis for predictions of sizable global warming due to observed increases in minor greenhouse gases such as carbon dioxide, methane, and chlorofluorocarbons”.

Of course, fossil fuels are finite. So, regardless of the scientific dispute on global warming, eventually we will have to switch entirely to renewable energy sources. However, the electricity production from renewable sources costs significantly more than that of coal and natural gas. For example, utility-scale solar electricity costs about four times more than coal-based electricity (see cost comparison of energy sources). To become cost-competitive, photovoltaic technology should become four times more efficient, which is theoretically impossible (see solar cell efficiency limits), or drop in price four-fold, which is unrealistic. Given this fact, the transition to alternative energy should be gradual and should not rapidly hit the economy and the consumers. Especially now, when the country is broke with a multi-trillion dollar debt, it’s not the right time to burden it with politically motivated regulations.

Power Supply Efficiency and Power Factor: Regulations Update

The U.S. Environmental Protection Agency (EPA) has recently announced that effective December 31, 2010, external adapters will no longer be eligible for the Energy Star label. The main reason for this move is in 2008 a mandatory federal minimum efficiency standard went into effect for adapters, mandating basically the same Energy Star performance level.

Last month the ENERGY STAR also published its Draft 3 revision to the proposed criteria for LED lamps, which can be screw into standard lamp sockets to replace incandescent bulbs. To earn the ENERGY STAR logo the LED lamp should have power factor ≥ 0.70. Of course, Energy Star is a voluntary program. However, chances are their requirements will be eventually incorporated in a federal standard. Also, Europe already requires lighting PF>0.9. These developments will certainly cause LED lamps manufacturers to use active power factor correction (PFC) circuits for LED drive. Given the efficiency and size requirements, it's likely that the SMPS designers would also have to use other techniques such as bridgeless PFC rectifiers and synchronous rectification.

"True" Bridgeless PFC Claims Power Supply Efficiency Increase

I am going to discuss Dr.Slobodan Cuk article entitled “The True Bridgeless PFC Converter Achieves Over 98% Efficiency, 0.999 Power Factor”. It was featured in the July issue of Power Electronics Technology Magazine. The article describes the latest invention of Dr.Cuk aimed at eliminating input bridge rectifier from the offline PFC power supplies and thus increasing their efficiency and power factor.
The bridgeless PFC circuits were known before. The diagram below compares Dr.Cuk’s circuit with a different circuit described in ST’s App Note 1606.

The Dr.Cuk approach is certainly novel and very interesting, just like probably all of his converter circuits. However, I believe the above article contains some exaggerations more suitable for advertising than for a technical paper.

For example, the author says: “This method also leads to a rather unusual converter topology consisting of three switches only: one controllable switch S and two passive current rectifier switches CR1 and CR2”. He also claims: “…The odd number of switches, three, is a distinctive characteristic of this converter with respect to all conventional switching converters…” However, later he admits: “…At present, a single MOSFET implementation is not possible due to built-in body-diode, so that switch S must be implemented by use of the two MOSFET devices connected in series at their sources and driven by a common floating gate drive circuit…” So, in reality, the switch S must consist of two real switches and overall there are still four switches, not three. When the power switch S in ON, the current flows through three switches: S1, S2 and CR1, which is a drawback of this converter. With respect to the conduction losses during the ON time interval, I see no improvement relative to the known circuit of a “bridgeless PFC”, in which ON-state current flows through only two switches, S1 and S2. For the same reason I would say, it is not more "true" bridgeless than the original circuit. I understand, the reduction of conduction losses in Cuk's circuit comes during OFF state of the switch when the current flows through a single switch CR2 while in the known circuit it flows though two switches, such as CR1 and S2. Therefore the main advantage of this circuit would probably be realized when ON time is low and OFF time is high. Since at low input line the duty cycle and ON-time tend to be high, while at high line they tend to be low, the advantage of the Cuk’s proposed converter would be at high input lines where PFC has higher efficiency anyway. The article claims 98% efficiency, but unfortunately it does not state under what input and output conditions it was achieved. I tend to doubt very much it is achieved at low line.

For more information see my review of schematics of various bridgeless PFC.

Meeting Energy Efficiency Standards for External Power Supplies

I previously wrote about the Energy Independence and Security Act of 2007 (EISA 2007). Its Section 301 establishes efficiency standards for external power supplies (EPS), such as power adapters. The U.S. Department of Energy (DOE) has recently published a Final Rule on "Energy Conservation Program: Certification, Compliance, and Enforcement Requirements for Certain Consumer Products and Commercial and Industrial Equipment." In this document under section 430.24 (bb), is the requirement for determining the number of EPS units to be tested to claim compliance with EISA 2007. In short, the DOE document requires 97.5% confidence level to reflect variations in materials, the manufacturing process, and testing tolerances.

The Section 24(bb) of Title 10 of the Code of Federal Regulations (10 CFR) Part 430 states:
For each basic model of external power supply selected for testing, a sample of sufficient size shall be selected at random and tested to ensure that—

(1) Any represented value of the estimated energy consumption of a basic model for which consumers would favor lower values shall be no less than the higher of: (i) The mean of the sample, or (ii) The upper 97.5 percent confidence limit of the true mean divided by 1.05;

and

(2) Any represented value of the estimated energy consumption of a basic model for which consumers would favor higher values shall be no greater than the lower of: (i) The mean of the sample, or (ii) The lower 97.5 percent confidence limit of the true mean divided by 0.95.

To demonstrate compliance with EISA 2007 standards for Class A EPSs (in effect since July 1, 2008), manufacturers must test representative sample of units according to the DOE test procedure, and certify their compliance by submitting a compliance statement and the first certification report to DOE by July 6, 2010.

To translate their language to plain English, when they say the "represented value of energy consumption for which consumers would favor higher values" they refer to the efficiency. Conversely, the "represented value for which consumers would favor lower values" is input watts. (Our lawmakers of course presume they know what we, the consumers would favor. Would you favor a charger with 51% efficiency over a charger with 49% if the latter one costs twice less?)

To determine the number of the samples to be tested to confirm the compliance with 97.5% confidence level, the manufacturers would have to revisit the statistical analysis theory. To be able to sell the affected external power supplies in US, they have to do the testing, the math, and to submit the required docs to DOE by 07/06/10.

Medical Power Supplies: New Efficiency Standards are Ahead

This week the U.S. Department of Energy (DOE) has published a notice of proposed rule on its "Energy Conservation Program for Consumer Products: Determination Concerning the Potential for Energy Conservation Standards for Non-Class A External Power Supplies." In this document, DOE proposes to determine that energy conservation standards for so-called non-Class A external power supplies (EPS). Class A in DOE terminology refers to single output EPS with nameplate power under 250 watts.

For reference, currently there are three domestic programs that mandate certain minimum efficiency levels of external power supplies: the Federal mandatory standard for Class A EPSs, the EPA’s voluntary ENERGY STAR standard, and California’s mandatory standard for so-called ‘‘State Regulated EPSs.’’ They all apply to low-power single-output units and particularly exclude medical supplies. Did you think the government would let anything to be unregulated? Nah! The DOE is now is trying to regulate efficiency of four more types of external power supplies that do not fall under class A: (1) Multiple output EPS (2) EPS above 250 W, (3) EPS for medical use, and (4) EPS for battery charging. The new proposed rule can affect power supplies for a wide variety of applications such as amateur radio equipment, Xbox 360, nebulizers for home use and other medical equipment, cordless power tools, etc. Note that this rule does not set any specific standards yet; it only positively determines that future standards may be warranted and should be explored in an energy conservation standards rulemaking. DOE will be accepting comments by December 18, 2009, after which it will make an actual determination.

Green Electricity From Cars

This week an Israeli firm Innowattech performed a successful trial of their alternative energy system that generates "green" electricity from vibration caused by passing cars. The system was installed on a 10 meter strip of asphalt on a highway and powered the street lights set up next to this strip. It used special piezoelectric generators embedded in the asphalt 2 inches below its top level. The generators were mounted with electronic cards that fed voltage into a storage system.

Piezoelectric effect in general is the generation of a voltage by certain solid dielectric materials when a mechanical stress is applied to them. It has been known for more then a century, and is widely used in piezoelectric transformers for high-voltage power supplies, various transducers, sensors, cigarette lighters, and other low-power applications. The Innowattech's system called IPEG™ is probably the first practical high-power application of piezoelectricity. According to the company, the installation of their system stretching one kilometer would produce 200 kW per hour on single traffic lane, or 1 megawatt on a four lane highway. Installation of the piezo-generators and electronic cards can be performed during paving of new roads or during the maintenance work. The "traffic energy" can be either supplied back to the drivers by powering the road lights or fed into the electric grid. A variation of IPEG™ can also produce power from pedestrian movement. Harvesting energy from the vibrations created by people walking on the floor is also being researched by East Japan Railway Company, who installed “Power-Generating Floor” in a Tokyo station.

Innowattech estimates the cost of energy harvesting from roads, railways and runways via IPEG™ to be 3 to 10 cents per kilowatt, which is comparable to the cost of renewable energies.

Power Supply Efficiency Compliance Calculator

I previously wrote about various US and international regulations related to an external power supply efficiency. Power Integrations came up with a nice free online tool that let you quickly check whether your charger or an adapter complies with the energy-efficiency regulations. You just enter your power supply's nameplate wattage, no-load power consumption and the efficiency in the active mode at various load levels. The calculator then tells you whether you meet various worldwide standards and actually displays the required no-load input wattage and required efficiency you need for the compliance.
The calculator currently checks for compliance to the following standards for PSU below 250W:
• ENERGY STAR (version 2.0), a voluntary standard sponsored by the U.S. Department of Energy and the EPA;
• EISA 2007 section 301, a mandatory U.S. efficiency standard, based on the California Energy Commission’s Appliance Efficiency Regulations;
• European Commission Code of Conduct (version 4) issued in April 2009;
• European Eco-design Directive: The Commission’s Eco-design Directive for external power supplies, which aligns with the EISA 2007 standard for Tier 1 and ENERGY STAR (version 2) for Tier 2;
• China USB Charger Specification (YD/T 1591-2006) for mobile telecommunication terminal equipment power supplies;
• EC Integrated Product Policy (IPP) for mobile phone adapters/chargers.

Hopefully, PI will be promptly updating their calculator when the applicable standards change.

CFL (Compact Fluorescent Bulbs) Pros and Cons

Speaking on April's 22 Earth Day about his energy plan, President Obama reportedly called on every American to replace one incandescent light bulb with one compact fluorescent (CFL).

Well, like all other devices CFL has pros and cons. For reference, compact fluorescent bulbs use up to 75 percent less energy then traditional incandescent lamps. However, they do present potential health and environmental hazards. I wonder if the president's advisers fully informed him of all the impacts of using these bulbs?

Last year a research by UK's Health Protection Agency has shown that CFL bulbs can emit unhealthy levels of ultraviolet radiation when they are in close proximity to people. They said that the UV levels can be equivalent to that experienced outside on a sunny day in the summer and some precaution is warranted. The Agency's chief has suggested: "We are advising people to avoid using the open light bulbs for prolonged close work until the problem is sorted out and to use encapsulated bulbs instead." Hmm... Maybe we should use at home sunscreen and sunglasses with UV protection to protect ourself from these "green" energy-efficient politically correct bulbs?

Of course, many of us are not concerned of prolong sunlight exposure and would spend long time under the sun. Nevertheless, this WHO's warning should be taken seriously: "Prolonged human exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye and immune system... Over the longer term, UV radiation induces degenerative changes in cells of the skin, fibrous tissue and blood vessels leading to premature skin aging, photodermatoses and actinic keratoses. Another long-term effect is an inflammatory reaction of the eye. In the most serious cases, skin cancer and cataracts can occur."

And although the above HPA's report says that when the CFL is further then 1 foot, the UV level is less than being outside on a sunny day in winter, for me it is not good enough. I personally don't want to subject my family to UV radiation [even a low-level one] for the sake of saving a few bucks, or helping a utility company, or because of anyone's political agenda.

Besides being a source of UV radiation, all CFLs contain mercury, a toxin that can cause kidney and brain damage (how come the state of California is not requiring the appropriate warning label?) Based on a research by Stanford University, the amount of mercury in one CFL bulb can contaminate more than 1,000 gallons of water beyond safe drinking levels. Now, raise your hands: who will bother bringing a burnt bulb to a special recycling place [if you can find one in your area] rather then throwing it in the trash?

And what if you broke the CFL? The EPA has a whole page of the clean-up instructions, which include the following sections:
Before Clean-up: Air Out the Room;
Clean-Up Steps for Hard Surfaces;
Clean-up Steps for Carpeting or Rug;
Clean-up Steps for Clothing, Bedding and Other Soft Materials;
Disposal of Clean-up Materials;
Future Cleaning of Carpeting or Rug: Air Out the Room During and After Vacuuming.

Hey, how about just staying with good old incandescent bulbs until a safe alternative will be developed? By the way, today's CFLs have a lousy power factor. For now a PF doesn't affect the residential electricity bills, but it does affect the utilities. Speaking about a safe alternative. If you are interested in $10 million cash, the US Dept. of Energy is offering this prize to create a solid-state screw-in replacement for the 60W bulb. If you can develop sufficiently bright LEDs and handle the packaging, give me a buzz- I would handle the AC-DC part of it, and we'll split the prize :-)

How to Measure Efficiency of a Multiple-Output Power Supply

On March 27, 2009, the US Department of Energy (DOE) published an amendment to its test procedures for battery chargers and external power supplies (EPS). The amendment includes provisions for measuring standby mode and off mode energy consumption and adds a test procedure for testing switch-selectable external power supplies. Since the document basically clarifies existing test procedures, which DOE originally could not formulate clearly, it is mainly clerical and would not be worth noting if not for one funny thing. The amendment still does not include a test procedure for multi-output power supplies because of "the number of stakeholder comments and the limited timeframe for this rulemaking." OK, here is a little background. The Energy Independence and Security Act of 2007 (EISA 2007) set Federal efficiency standards for certain types of adapters and single-output EPS for consumer electronics. DOE has a test procedure to verify this efficiency. However, this procedure [which is basically: multiply output volts times amps and divide by the input power under various loading conditions] was written for single-output power supplies. It has therefore left out a significant group of products, powering applications such as radio transceivers, video game consoles, and printers. On August 15, 2008, DOE proposed a procedure for the testing of multiple-voltage external power supplies. On page 6 of the Proposed Rule we read: "DOE is not aware of any existing test procedure developed specifically to measure the efficiency or energy consumption of multiple-voltage external power supplies." Huh? Millions of multi-output power supplies both external and internal including PC PSUs are being built around the world and tested for Energy Star® and 80 PLUS® efficiency compliance. Folks, how about this: take a 5th grader, ask him/her to add up volt-amps of all outputs, divide by the input power, and you are done! Seriously, the main obstacle for DOE seems to be the loading profile. The PSU's nameplate power is often smaller than the sum of the nameplate power of each individual output. So what's the big deal? Derate (scale down) the loads of all the outputs proportionally, so that their sum does not exceed the limit for the entire power supply. Of course, it would not be the worst case efficiency (which you would probably encounter if you shift the bulk of the load onto the lowest voltage outputs), but it would be kind of typical efficiency. Back in 2006, at the APEC conference, EPRI Solutions and Ecos Consulting presented their Enhanced Proportional Allocation Method for Loading Power Supply. Their method is incorporated by Intel in its PC power supply guides. DOE did propose to adapt the ‘‘proportional allocation’’ method. Nevertheless, the DOE 2009 final rule still reads: "Due to the limited time provided by EISA 2007 and limited resources available prior to the publication of this final rule, DOE was unable to address the large number of stakeholder comments received and decided to defer action on multiple-voltage EPSs to a 2009 rulemaking." In a private sector usually a new power supply will be designed, built and tested in this timeframe or in a shorter one. It's entertaining to watch how long will it finally take for US DOE to make up their mind on how to test the efficiency and to move to something else.

Efficiency Standards for Power Adapters

In a previous post I wrote about various programs and regulations aimed at increasing PSU efficiency.

Here is a brief update. On December 19th, 2007, the Energy Independence and Security Act of 2007 (EISA 2007) that is intended to reduce US Oil Dependence, became law. Although the act is aimed mainly at improving vehicles fuel economy and increasing the production of clean renewable fuels, it contain sections that affect power supplies.
Particularly, Section 301 External Power Supply Efficiency Standards establishes energy conservation standards that take effect on July 1, 2008 for so called “Class A External Power Supplies,” and establishes the processes to review and possibly amend those standards.
The term "class A external power supply' means basically a single output low-voltage AC-AC or AC-DC converter under 250W that is intended to be used with a separate end-use product.
According to this law, a class A external power supply manufactured on or after July 1, 2008 should meet specific efficiency standards depending on its nameplate power Po. For example, in the power range from 1 to 51 W [which is typical for most adapters] if you convert EISA requirement into percentage, the minimum efficiency in active mode should be 50% + 9*Ln(Po), where Ln(Po) is natural logarithm of the nameplate output power.

EISA 2007 requires US Depratment of Energy to issue a final rule prescribing energy conservation standards for battery chargers, if technologically feasible and economically justified, by July 1, 2011. DOE will also have to complete the determination on non-Class A external power supplies by a new deadline of December 19, 2009.

Note that unlike voluntary Energy Star® and 80 PlUS® programs, the above requirements are mandatory.