Application Solutions

External Power Supply Efficiency Standards

Posted by Dulcie on July 6, 2018

External power supplies (EPS) are extremely widely used in households around the world to charge phones or operate tablets, laptops, game consoles and a variety of consumer electronic and electrical items.

Studies on European energy use of these power supplies indicate that reducing off-load power consumption and improving product efficiency will save nearly 10TWh of power each year. A Terawatt hour (TWh) is 1,000,000,000,000 Watts used in an hour. Reducing energy usage saves money, reduces the requirement to add new power generating capacity and cuts environmental pollution.

Two parameters were originally specified to regulate waste energy reduction, the maximum off-load power consumption and the minimum average efficiency level, which when multiplied by a billion products becomes very significant.

More often than not, many power supplies are left plugged in to the AC supply and fully operational; even when the device it was charging has been removed. Although the power supply is not powering anything, it still consumes power. The maximum off-load power consumption varies with the output power of the EPS and is stated in the specification.

With loads less than the full rating of the EPS, the efficiency of the power supply can decrease significantly. Low load conditions occur as a battery becomes partially charged, or when a device goes into an inactive (sleep) mode. External power supplies rarely remain in a 75 to 100% load condition.

First legislation began to be announced in 2004, starting with the California Energy Commission’s (CEC) intent to restrict the sale of non-efficient external power supplies. The USA, EU, China and a host of other countries and regions followed over the next ten years with increasingly tighter legislation.

In 2014, the EU issued a voluntary Code of Conduct (CoC) version 4, running in parallel with the mandatory Ecodesign Directive 278/2009. Also in 2014, the Department of Energy (DoE) published their Energy Efficiency Level VI standard.

February 2016, the Level VI standard became law in the US. The EU issued the more stringent version 5 CoC Tier 2 voluntary standard that was supposed to go into effect January 2018. That has been delayed and mandatory implementation is expected shortly.

Table 1 shows some of the differences for a single output, basic voltage power supply between these two newest standards. Efficiency limits have been given for a power supply rated between 49 to 250W. Please consult the relevant US and EU websites for the full specifications.

Table 1: A comparison between the latest US and EU regulations

Average efficiency measurements are required at four load conditions; 25, 50, 75 and 100%. These are added together and divided by four to produce an average efficiency figure.

Note, the EU has added a minimum efficiency level at 10% load.

The USA now includes power supplies that are rated at greater than 250W.

The term external power supply is defined by the US Department of Energy as one that is used to convert household electric current into DC current or lower-voltage AC current to operate a consumer product. Currently, the US grants exemptions for supplies powering FDA approved medical devices.

Modifying a power supply to meet a decrease in off-load power consumption is not a simple component change. The control IC often has to be switched to one that draws less power and energy saving techniques like pulse skipping implemented. Changes to primary side circuitry requires resubmitting the products to have the safety certifications updated. Both the redesign and submittal process are expensive and older products are often obsoleted as a result of this.

EU CofC Tier 2 and US Efficiency Level VI legislation is only applicable to external power supplies for consumer products. As TDK-Lambda targets the industrial market, rather than the suppliers of mobile phones, tablets and laptops, it is exempt from this legislation. However, to ensure our customers benefit from reduced off-load power consumption and improved product efficiency, TDK-Lambda has a number of external power supplies in the DT series that meet all the latest requirements, with ratings up to 300W.