How power supply efficiency has evolved

The latest DoE energy efficiency requirements won’t be the last. Here are a few of the changes in efficiency regulations the power supply industry can expect.

Authored by Inventus Power

As early as the 1990s studies showed that smaller external power supplies — such as those powering cell phone chargers, game boxes, cordless phones, and so forth — were becoming a major source of energy demand and were growing explosively. It also soon was obvious that the reduction of energy consumption in power supplies sitting idle but connected to power lines was even more important to reducing overall power consumption. Thus began demands that the power supply industry build more efficient power supplies to reduce the waste in energy consumption.

In 2004, California became the first government organization in the U.S. to declare legal energy efficiency requirements, followed by the U.S. government with the Energy Star program, a voluntary but not mandatory requirement for efficiency. When the DoE first came out with its proposal for efficiency standards, the reaction from the power supply industry was enormous and severe. The new standard was to be 88% at 50 to 250 W, with a sliding scale of 85 to 88% between 18 and 50 W, and a maximum no-load input draw between 0.1 and 0.21 W. The previous requirements were also a sliding scale to 49 W, with 80% at 18 W, and 86% at <49 to 250 W, and between 0.3 and 0.5 W at no-load. The biggest changes were expected in the lower powered units, nearly a 10% improvement at 18 W, where factors like voltage drop through the output cable is a fixed loss.

On top of the overall efficiency, the no-load power consumption was to drop to nearly one-third the current requirements. All the changes needed to bring power supplies into compliance with the technology available at that time forced the loss of features that consumers wanted, such as removing LEDs and shortening cables from the typical six feet to four feet, or even to just two feet. Even with those changes, power supply engineers were saying they could barely meet the requirements and still maintain a reasonable cost; initial forecasts from the industry were suggesting a two-dollar-per-unit rise in price to the consumer.

Consequently, the DoE delayed issuing the ruling by almost a year. During that time, the LED industry made significant advances in brightness while dissipating considerably less power. The designers of power supply control chips also took that time to devise new control chips able to realize higher efficiencies, particularly by boosting efficiency levels at lighter loads (~25% of full rated power). When the DoE did release requirements in 2014, the industry had better technology and components to comply with the new regulations.

Still the changes are not without cost. The two-dollar boost was no longer a concern, because the price of power supply controllers has come down as higher volumes and improved efficiencies allowed manufacturers to reduce box size. These improvements offset much of the cost rise, but there were also additional expenses. New control chips forced new design layouts, new production fixtures, new safety certificates, and managing soon-to-be obsolete product stocks.

At Inventus, we also found errors in the first control chips released for higher power levels, i.e. 150 W+, which delayed development programs until improved versions were ready. Many power supply companies came out with new model numbers that forced customers to reopen their safety files at an average cost of $8K to $10K each. Roughly half our OEM customers of information technology equipment (ITE) power supplies had to requalify our products.

We chose to keep the same model numbers so our OEM customers could minimize updates to their safety reports. But we recommended they at least perform a system evaluation and repeat their EMI testing. Even with an external power supply, EMI must be tested with the entire assembly. While our EMI profiles are close to those of our previous power supplies, they are not exact. If one of our frequency peaks happened to shift slightly closer to that of the main system, the combined EMI at that frequency could exceed allowed limits, forcing additional design work.

Additionally, all power supply manufacturers had to finish their design and agency approvals within two years. The reason was OEM customers needed time to complete their evaluation and clear out their inventory before the February 2016 deadline.

There continues to be confusion in the market as to whom the new standards apply. The standard is ~80 pages long, with only a few pages specifying the requirement, the rest explaining the reasoning behind the final version. There are lots of suggested inputs from people in the industry which, if you don’t realize you are reading a suggested input, can be misunderstood to be part of the requirement.

Additionally, the power supplies the commission tested are all from electronics found in the home such as cable boxes, game boxes, and toys. The commission only found one multi-output power supply in everything they tested, in a game box. But we know that multi-output power supplies, although declining, still find use in the industrial world. One might infer that the standard aims at home-based applications, though this is never explicitly stated. The obvious ambiguity has led many industries to require the standard in their non-consumer products to safeguard against future problems, while also being able to advertise their use of the latest technology.

As efficiency requirements are becoming ever stricter. The European Union’s Code of Conduct (CoC) Tier 1 came out as a voluntary requirement in January 2014, mostly harmonizing the EU with US DoE Level VI. The main difference between the two is a slightly less severe no-load consumption requirement. Its adoption as an EU Ecodesign rule is currently under review with a targeted implementation date sometime this year.

The EU’s more stringent CoC Tier 2 requirement became effective on a voluntary basis in January 2016 and is also under review to become law as an Ecodesign rule, potentially in 2018. The key difference between the CoC Tier 2 and Level VI is a new 10% load efficiency measurement, which imposes efficiency requirements roughly 10% lower than the overall requirement when the power supply is running at 10% load. The control chips designed to meet Level VI efficiency should allow most supplies to meet the new requirements, but all designs will need to be rechecked for compliance. Historically most power supplies have been terribly inefficient at light loads, considered to be anything under 25% of full load.

Efficiency requirements are not the only changes in power supply regulations. Sometime this year the EU is expected to release its approval of a new agency standard 62368-1. This new standard combines the Information Technology and the Audio-Visual standard into one document. The US has decided to grandfather-in any device which already has 60950-1 approval but will require testing to 62368-1 for new submissions as of June 20, 2019. The EU is expected to declare that to maintain a CE mark, products must be re-certified to 62368-1. No design changes should be needed, but it’s another cycle of testing and reports to be borne by the power supply manufacturers and their customers.

As consumers of electric power, we appreciate the savings efficiency regulations bring both in our own electric bills and in avoiding the need for additional power plant capacity. However, the stricter efficiency needs have brought a high turnover in products over the last three years, and the trend is expected to continue. Gone are the days of a design having a graceful retirement after ten years. Companies that want to stay relevant in the market now need to plan on continuing updates and engineering costs to support their products.