New Adapter Regulations for a More Efficient IoT

The latest Level VI external power supplies enhance the efficiency of line-powered Internet of Things gateways

Tens of billions of “things” are set to be connected to the Internet over the next few years, but not all will be individual IP-addressable sensors. Many will be gateways that concentrate data received from arrays of devices via links such as Bluetooth® or proprietary low-power radio, or wired point-to-point or fieldbus connections. With these devices included, the Internet of Things (IoT) could be gathering data from more than a trillion sensors to be processed and stored in The Cloud.

Much IoT design analysis is focused on ultra-low-power design, enabling endpoints such as smart sensors to run for long periods powered by a battery or by energy harvested from the ambient environment. Gateway devices require significantly more power than a small battery or energy-harvesting system can provide.

Unlike sensors, which must be placed in specific locations, gateways allow more flexibility to position the device near a convenient source of power such as an AC wall outlet. If an external power adapter is used to provide the low-voltage DC supply for the gateway, designers can simplify the gateway’s internal circuitry and outsource the responsibility to comply with power safety and efficiency standards to the adapter supplier.

Making Adapters More Efficient

Designers of all sorts of OEM systems have been choosing to power their designs with an external adapter for several decades now. In fact, adapters have been so successful that researchers as long ago as the 1990s foresaw a future powered by billions of the devices. A 1998 study by Alan Meier of Lawrence Berkeley National Laboratory (LBNL) estimated that about 5% of total residential electricity consumption in the US – worth about $3 billion – was wasted by power supplies while the connected equipment is in standby mode. The percentage was predicted to reach 30% within 20 years if no action was taken.

The first mandatory energy-efficiency specifications for external adapters came into force in California in 2004. Similar standards were adopted worldwide, and became harmonized as the International Energy Efficiency Marking Protocol for External Power Supplies. Evolution of the protocol has imposed increasingly stringent limits on no-load power consumption and minimum average operating efficiency.

In 2014, the US Department of Energy (DoE) announced that all external power supplies (EPS) manufactured after February 10 2016 and marketed in the US must meet the new Level VI efficiency specification. The EU and other authorities, currently operating to Level V specifications, are expected to raise their own requirements to Level VI soon, although none have yet announced official regulations.

The new ruling applies to all external power supplies, whether they are shipped as standalone products or in the box with OEM equipment such as notebook PCs, smartphones, tablets, printers, Internet hubs, routers, and IoT gateways. Given the expectation for explosive growth in IoT applications, the Level VI specification for external power supplies could be seen as providing valuable protection for the environment against the effects of the large numbers of IoT gateways soon to be connected to the power grid.

CUI began introducing Level VI products to its EPS range in late 2014, to address the new regulation. EPS manufacturers typically adjust their product portfolios to meet the highest mandatory standard, which enables OEM customers to maximize operational efficiency and eliminate supply-chain errors by shipping a common power supply type with products destined for multiple export markets.

The Level VI protocol is significantly more complex than its predecessors, and defines five categories of adapters including, for the first time, units rated over 250 W. Table 1 lists the specified no-load power and average efficiency for all categories covered.

Table 1. Summary of no-load and dynamic efficiency targets for Level VI marking protocol.

Typical IoT gateways are unlikely to require a 250 W or multi-output adapter, but could be designed for use with a single-voltage AC/DC supply of above 6V or a sub-6V low-voltage supply in the under-1W or 1W-49W category. Figure 1 compares the minimum average efficiency specifications for Level VI single-voltage (output > 6V) power adapters against the Level III, Level IV and Level V specifications. The limit is significantly higher for units in the 0.5W-5W range that will likely power a large proportion of IoT gateway devices. Depending on the application the gateway may be designed to make use of sleep modes, taking advantage of the lower no-load power consumption of the Level VI specification. Other applications may require the gateway to be active more or less continuously.

Figure 1. The Level VI minimum average efficiency requirement is significantly higher than in previous specifications.

Meeting Level VI by Design

The new Level VI specifications present tough challenges to power supply designers. Compared with CUI’s Level V power supplies, the Level VI units incorporate changes to almost every aspect of the primary and secondary-side circuitry. These have included designing-in the latest control ICs that support enhanced light-load operating modes: in normal operation the new controllers operate at the same 65 kHz switching frequency used in the Level V products, but change to 22 kHz at light-load and no-load to reduce power loss and improve efficiency. The capacitor and resistor values in the secondary feedback circuit have also been re-optimized to mitigate the effects of increased ripple and noise at lower switching frequencies. The control IC also takes advantage of new technologies to reduce quiescent power, which contributes further towards meeting the tougher maximum limits on no-load power consumption.

Changes in the secondary-side circuitry of low-voltage/high-current Level VI power supplies include adopting synchronous rectification using MOSFETs and a dedicated control IC, in place of simple diode rectification. Other component changes include re-optimized resistance values, and the use of increased wire gauges to reduce internal power dissipation. Moreover, newer MOSFETs with lower on-state resistance help to raise efficiency at heavier loads.

On the other hand, the main power circuitry is arranged in much the same way as the previous Level V units. Units rated below 120 W use CUI’s established flyback design, while adapters over 120 W use LLC resonant topology. It is worth noting that the increased average efficiency of the Level VI power supplies also helps to reduce the typical working temperature thereby boosting reliability. This can be a particularly important advantage in IoT applications, where equipment often is required to operate for long periods in the field with little or no maintenance.

Improvements for IoT and Environment

The US Environmental Protection Agency (EPA) has said the regulations imposed on external power supplies over the last decade have already cut CO₂ emissions by more than 24 million tons per year and saved households $2.5 billion annually. The US Department of Energy[1] now believes enforcing Level VI will save around 47 million tons of CO₂. Manufacturers of equipment such as IoT gateways need to keep abreast of the latest standards applicable to power supplies and energy.

[1] Energy Conservation Program: Energy Conservation Standards for External Power

Supplies: https://www.energy.gov/sites/prod/files/2014/02/f7/eps_ecs_final_rule.pdf