(First published in Components in Electronics magazine)
External power supplies: New standards drive new design priorities
Due to the ever-increasing impact humans are having on the environment, it is important that our devices work to counter the adverse effects that can result from everyday life and business. External power supplies (EPSs) have a unique opportunity to positively impact this effort. Contained and operating separately from the devices they power, electric power supplies contribute substantially to total global electricity consumption. Because of this, resolving the inefficiencies of power conversion can add tangible environmental value across the globe, for example cutting energy consumption and reducing CO2 emissions. Competitive value follows as well, with EPS designers empowered to redirect saved kilowatts into different applications. Newer, more eco-friendly systems can differentiate a product, ultimately increasing market share. EPS designers must embrace the regulations and energy conservation initiatives at play and plan for continued evolution of ecological concerns worldwide.
Understanding new and developing standards
A number of new, often parallel, regulations are advancing energy conservation in EPS design, formally recognising the relationship between today’s lifestyles and electrically powered devices. Overall, the goal is to ensure the EPS features a high average energy efficiency and minimum no-load power consumption. Level VI standards, regulations developed by the U.S. Department of Energy (DOE), went into effect in 2016. The European Union (EU) followed suit with its Tier 1 and Tier 2 Code of Conduct (CoC) standards, established by the European Commission Joint Research Centre; these standards are currently voluntary and anticipated to become binding in the future.
Decreasing energy consumption via Level VI standards
Two key performance criteria are defined by the DOE’s Level VI regulations: no-load power consumption and minimum average efficiency limits in active mode. These are measured at 25 per cent, 50 per cent, 75 per cent and full load, and span a broad range of products including:
- Single-voltage external AC-DC power supply, basic-voltage (output voltage ≥6 V)
- Single-voltage external AC-DC power supply, low-voltage (output voltage below 6 V)
- Single-voltage external AC-AC power supply, basic-voltage (output voltage ≥6 V)
- Single-voltage external AC-AC power supply, low-voltage (output voltage below 6 V)
- Multiple-voltage external power supply
Table 1 features minimum average efficiency thresholds and the maximum standby power EPSs falling into the above classes.
The DOE’s Level VI legislation is more stringent than previous regulations, incorporating an entirely new category of multiple-voltage EPS options as well as a new output power level threshold of 250W. Table 1 defines a multiple-voltage EPS as ‘an external power supply designed to convert line voltage AC input into more than one simultaneous lower voltage output,’ while the ln(Pout) designation refers to the natural logarithm of an output power.
The DOE ruling also differentiates between direct and indirect operation EPSs. For example, direct options are external power supplies capable of operating a consumer product that is not a battery charger, without the assistance of a battery. The majority EPSs falling into the direct operation category shall comply with the parameters illustrated in Table 1. The new standards (Level VI) apply to direct operation EPSs only, but not all of them have to be compliant as the standards state certain exceptions.
An indirect operation EPS cannot power a consumer product (other than a batter charger) without the assistance of a battery. For example, if an end-use product only functions when drawing power from a battery, the EPS associated with that product is classifid as an indirect operation EPS. DOE developed this method to distinguish between direct and indirect operation EPSs, which requires manufacturers to determine whether an EPS can operate its end-use product once the associated battery has been fully discharged.
Understanding the evolving EU Code of Conduct (CoC)
Like the DOE, the EU proposes to minimise energy consumption of external power supplies, under both no-load and load conditions. Still under revision and pending formal legislative approval, the EU has defined two separate sets of provisions, known as Tier 1 and Tier 2. Tier 1 most closely resembles the DOE’s Level VI rulings, with certain important differences such as implementation of a new 10 per cent measure in addition to a four-point average efficiency in active mode. There is no distinction between direct and indirect EPSs, and high-power EPSs (Pout > 250 W) are not a subject of the regulations. Tier 2’s CoC is more ambitious and stringent, increasing performance requirements above the DOE’s Level VI standards as well as the EU’s Tier 1 for both no-load power consumption and the minimum average.
Planning for the future of EPS design
A smart, proactive approach can be achieved by implementing the latest technologies and topologies with inherently higher efficiencies and low standby power features. However, addressing these new standby and efficiency requirements must not impact the quality of EPS performance. Technologies must be chosen carefully, considering all performance parameters for any specific applications. For example, switching regulators equipped with frequency-reducing features to boost light-load efficiencies may worsen output voltage – these are the kinds of parameters that can create unexpected end-user impact, or even render the product unsuitable for certain applications if the burst mode is within audible frequency range.
Just as the DOE’s Level VI specifications became mandatory, the EU’s Tier 1 and Tier 2 proposals will certainly formalize soon. Power supply design engineers and manufacturers should be prepared for inevitable changes required to meet key performance criteria. Further, compliance with these types of standards is likely to be an evolving challenge, as environmental concerns continue to feature in legislation worldwide.
Environmental responsibilities in the design realm will only increase, providing engineers and manufacturers with a unique opportunity in a changing market. Compliant products will reduce costs and enable new applications with saved kilowatts. And reducing energy consumption and CO2 emissions is a highly competitive way to differentiate products, performance and market leadership.
(First published in Components in Electronics magazine)