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.
The internet of things (IoT) could be gathering data from vast numbers of sensors to be processed and stored in the cloud.
Design analysis for the IoT is focused on 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.
Adapters can be efficient
Designers of all sorts of OEM systems have been choosing to power their designs with an external adapter for several decades now. Adapters have been so successful that researchers as long ago as the 1990s foresaw a future powered large numbers 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 $3bn – 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 in came into force in California in 2004.
Similar standards were adopted worldwide, and became harmonised 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.
Today, all external power supplies marketed in the USA and Canada must meet the protocol’s Level IV specification, and must display a Roman numeral IV on the nameplate.
The EU currently imposes the stricter Level V specification.
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 higher Level VI efficiency specification.
The EU and other authorities can be expected to raise their own requirements to Level VI soon after, although none have yet announced official regulations.
The new ruling soon to come into force in the US will apply to all external power supplies, whether they are shipped as standalone products or in the box with OEM equipment such as PCs, smartphones or routers.
Given the expectation for explosive growth in IoT applications, the Level VI specification for external power supplies could provide valuable protection for the environment against the effects of the large numbers of IoT gateways soon to be connected to the power grid.
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 below lists the specified no-load power and average efficiency for all categories covered.
Typical IoT gateways are unlikely to require a 250W 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.
The graph below 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.
Meeting Level VI by Design
The new Level VI specifications present tough challenges to power supply designers. Compared with 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 65kHz switching frequency used in the Level V products, but change to 22kHz 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 in existing Level V units. Units rated below 120W use an established flyback design, while adapters over 120W 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 $2.5bn annually.
The US Department of Energy 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.
Level VI power adapters are already available, to help ensure compliance as soon as the new specification comes into force from 10 February.
Jeff Schnabel is vice-president of marketing with CUI