5 min.

Driving an Efficiency Stake Through the Heart of Vampire Power

Vampire power, standby power, no-load power, phantom load, leaking electricity – whatever you choose to call it, the fact is that many AC/DC power supplies and electronic devices consume energy even when they are not in use. Which, in many cases (think of fast chargers for mobile phones, television power supplies or adapters for digital assistants that may be plugged in 24/7 but only actually operate for a few hours a day) could be the vast majority of the time. And while this power consumption may be considered minimal in the context of a single product, with so many ‘always on’ internal and external power supplies deployed worldwide (and that number continuing to grow) the cumulative global power drain has a significant impact on both global energy use and greenhouse gas emissions.

Indeed, a few years ago, the Lawrence Berkeley National Laboratory estimated that energy from devices on standby accounted for anywhere between five and 10 percent of the total electricity used in residential homes and for one percent of the world’s carbon dioxide emissions. And in 2015, the Natural Resources Defense Council (NRDC) in the USA concluded that phantom load electricity represented nearly 23% of energy use in a study of Californian homes. The NDRC went on to estimate the always-on energy used by inactive devices in the USA annually at around 150 billion kilowatt-hours – that’s around half of Italy’s total electricity demand in 20191.

The sheer scale of the issue has prompted governments and agencies to create initiatives and legislation designed to curb no-load power consumption. Among these are Europe’s ‘Ecodesign’, a voluntary code of conduct that limits maximum vampire power to 75mW for power supplies up to 49W and 150mW for power supplies rated at 49 – 250W. In the USA, the DoE has created the external power supply (EPS) Level VI efficiency standard that sets 100mW and 210mW as the limits for the same power ranges.

However, with global energy prices rising and recent climate events further underlining the importance of designing for sustainability, there is still more that power supply manufacturers could be doing.

In particular, they need to look at solutions that flatten the efficiency curve so as to minimise energy losses across the full range of potential operating conditions, from no-load to full-load.

Flattening the No-Load to Full-Load Efficiency Curve

As you might expect from a company that focuses on delivering revolutionary power electronics for a better planet, Eggtronic has been at the forefront of developing AC/DC solutions that not only optimise efficiency when power conversion is at full load but at all levels of power.

Take, for example, the company’s recently launched SmartEgg single-stage switching PFC and regulator design shown below.

SmartEgg ZVS-based AC/DC converter architecture

Targeted at applications in the 75 to 1kW range that need output voltage regulation and power factor correction (PFC), SmartEgg technology employs a technique that forces zero voltage switching (ZVS) under every load condition. The result, as the following graph illustrates, is the ability to deliver efficiencies of up to 95% at full load and 92% at light load – a significant improvement over conventional approaches.

Efficiency curve for SmartEgg vs conventional approach of boost PFC and LLC stages

What’s more, compared to traditional medium-power AC/DC PFC architectures that employ a boost PFC input stage and an LLC stage that controls the output voltage, SmartEgg halves the number of MOSFET and magnetic components required by replacing these two stages with a single-stage converter capable of controlling both input current and output voltage. This has further implications for environmental sustainability as it reduces the number of components that need to be both manufactured and shipped and results in smaller, lighter power supplies that further reduce transportation overheads.

To see how improved low-load efficiency translates into potential real-world power savings, consider the example of a TV with a pretty typical idle load of around 1W. If power conversion is based on Eggtronic’s SmartEgg technology operating at an efficiency of 92% versus a more conventional approach with a light-load efficiency of 72% then the power loss is 0.1W versus 0.43W - a saving of 0.33W. For a TV that is in standby for 21 hours a day (in 2020 it was estimated that the average person watched three hours of TV a day) that would be an annual saving of almost 2.6kWh. If the power converters of all the TVs in the world (currently estimated at 1.8 billion2) could be replaced with SmartEgg technology then that would be a global saving of 4.68TWh (ignoring peak efficiency and logistics advantages). That’s the equivalent to saving 7.5 million barrels of oil and an environmental benefit on par with growing around 54 million trees from seedlings in 10 years3.

And, of course, that is in addition to the savings that come from the improved efficiencies during the three hours a day that the TV is on. Obviously different TVs have different power consumptions but if we assume an average of 70W the Eggtronic solution offers an efficiency improvement of 1.5% over the conventional approach (95% versus 93.5%), which results in a power saving of 1.2W per TV. Following the same logic as above, that would deliver a further global saving of almost 2TWh (or 3.2 million barrels of oil).

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