With the aims of reducing energy wastage and improving distribution-network stability, regulatory authorities within the EU and US have been steadily introducing a series of measures that power-supply and equipment designers must consider. In the first instance, these measures specifically target no-load consumption and conversion efficiency for external power supplies of up to 250W—principally because these assemblies sell in huge numbers, are very often permanently connected to the ac-line supply, and typically lack an on/off switch so tend to spend long periods in standby or no-load modes. Amazingly perhaps, the European Commission (EC) estimated that wall chargers and similar devices left in standby lost as much as 8 TWh throughout the region in 1996—or about the annual electricity consumption of small nations such as Georgia or Iceland—and that this figure would almost double within a decade.

But it was over in the US where rolling blackouts were becoming increasingly common occurrences that the California Energy Commission (CEC) first developed the legislation that underpins today’s US Energy Star and EC Code-of-Conduct programs. Many other territories have adopted similar measures making it imperative to meet these requirements. The evolutionary nature of their development means that the requirements vary slightly between territories, leading to some confusion that requires rationalising. Firstly however, it’s worth examining what is and what is not subject to regulatory attention.

Energy Star, the CEC, and Federal requirements
The situation is complicated in the US by the fact that there are three interested parties—the CEC, the US Environmental Protection Agency (EPA) and Department of Energy (DOE) and the country’s Congress. The CEC’s 2007 Appliance Efficiency Regulations carry the force of state law, but as many other states have adopted the CEC’s stance, this document effectively becomes a federal mandate (reference 1). Participation within the EPA/DOE’s Energy Star program is supposedly voluntary, but the Energy Independence & Security Act (EISA) that President Bush signed into law in 2007 (reference 2) has the force of federal law and effectively makes many aspects of Energy Star compliance a legal requirement—notably including Section 301, which outlines the standards for so-called “class A” external power supplies (EPS) that originate from the CEC. Here, the DOE states that in general, the term class A external power supply means a device that:

• is designed to convert line voltage AC input into lower voltage AC or DC output;
• is able to convert to only one AC or DC output voltage at a time;
• is sold with, or intended to be used with, a separate end-use product that constitutes the primary load;
• is contained in a separate physical enclosure from the end-use product;
• is connected to the end-use product via a removable or hard-wired male/female electrical connection, cable, cord, or other wiring; and
• has nameplate output power that is less than or equal to 250 watts.

There are a limited number of exclusions that comprise any device that:

• requires Federal Food and Drug Administration listing and approval as a medical device, or
• powers the charger of a detachable battery pack or charges the battery of a product that is fully or primarily motor operated.

Supplies that are intended for use as spare parts for products made before 1st July 2008 are similarly exempt, as are supplies that will be exported outside of the US.

The limits that apply throughout the US are:


This approach mirrors the standards that the CEC imposed as of January 1st, 2008 and is very similar to Energy Star V1.1. The current Energy Star V2 version (reference 3) that became effective on November 1st, 2008 and is widely recognised as today’s benchmark demands:


The reference to “low voltage models” in the top table of figure 2 signifies devices that output less than 6V at currents of 550 mA or more. The requirements for no-load operation are common to all models:


One point that’s worth remembering is the difference between no-load and standby operation. This differentiates between a supply simply being left on and not supplying any load current, and a supply outputting current to keep some circuitry active. That is, when the specifications say “no load”, 0% of full output power capability is what they mean.

Also notice the reference to “minimum average efficiency”, which is a four-point average of the active-mode efficiency performance that’s measured at 25, 50, 75, and 100% of full output or “nameplate” power. The CEC’s “Test Method for Calculating the Energy Efficiency of Single-Voltage External Ac-Dc and Ac-Ac Power Supplies” describes the test methodology and report format that is necessary (reference 4), and it is this document that all applicable US and EC standards use. The CEC requires that an approved laboratory undertakes testing, but this stricture does not apply elsewhere. Figure 4 shows some examples of applying the formulae that figure 2 describes:


Clearly, any qualifying power supply that’s for sale throughout the US must meet whichever is the stricter set of requirements that apply to its particular output power level. In addition, any supply with an input power demand of 100W or more must have a true power factor (PF) of 0.9 or better when tested at full load current. As EC legislation already tackles 230V/50Hz supplies in the guise of EN 61000-3-2’s harmonic current limits, this PF requirement only applies to supplies that operate from 115V/60Hz. Supplies that operate at both voltages must meet both sets of requirements.

The EC’s Code-of-Conduct
While closely following the US models, the situation within Europe is different in two respects—the limits for no-load consumption are currently slightly stricter for mobile chargers and will become much stricter as of 2011, and the applicable Code-of-Conduct (CoC) is just that, as it currently lacks legal powers in enforcement terms. Instead, power-supply manufacturers are encouraged to commit to meeting CoC targets, and those signatories report the percentage of their output that meets these targets on an annual basis. But for any reputable power-supply manufacturer, the result is the same and it remains imperative to ensure that their products are fully compliant.

The current version 4 of the CoC was published in April 2009 (reference 5). It has similar scope as its US counterparts in defining external power supplies that in this case output 0.3 – 250W rather than 0 – 250W, and it uses exactly the same test methodology. It also differentiates between low voltage and other supplies in the same way as the US, i.e. an output voltage of less than 6V together with a current of 550 mA or more qualifies as low voltage. Moreover, the active-mode efficiency limits mirror those of Energy Star V2 with the single exception that the CoC does not include a limit for low-voltage supplies of more than 49W output—presumably because the EC perceives the population of say 5V/10A external supplies as being insignificant in the consumer-level applications that this part of the CoC primarily targets. No-load power consumption similarly follows Energy Star V2 for standard supplies, but the CoC makes more stringent demands for mobile chargers as figure 5 shows:


Ensuring Compliance
Standard marking practices make it easy to identify supplies that comply with the respective specifications. To signify compliance with today’s CEC and EISA requirements, a Roman numeral IV must appear on the product’s label, while a V indicates that the supply meets Energy Star V2—and by extension for standard supplies, the EC’s Code-of-Conduct V4 as well. Typically, text to the effect of “efficiency level” accompanies this marking.

All of XP Power’s current catalogue products meet the CEC and EISA requirements. For example, the AEF series of 100 – 150 Watt AC/DC power supplies meet the requirements of Energy Star V, CEC and EISA. It’s important to recognise that today’s specifications and regulations are subject to continuing evolution with the result that limits are likely to become more demanding. XP Power’s commitment to continuous product improvement ensures that its supplies will continue to meet or exceed any applicable regulatory requirements, while a specific focus on maximising efficiency and minimising no-load operation drives down cost-of-ownership. A developing line of internal component power supplies with very low no-load consumption is further evidence of the company’s dedication to maximising energy efficiency for all types of end-user equipment.

Ref. 1. 2007 Appliance Efficiency Regulations, California Energy Commission, December 29th 2007.

Ref. 2. Energy Independence and Security Act 2007,

Ref. 3. ENERGY STAR® Program Requirements for Single Voltage External Ac-Dc and Ac-Ac Power Supplies, Eligibility Criteria (Version 2.0),