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26/11/2015

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 1agld1r.gifPowering IoT: How Next Generation of External Power Supplies will Help Minimize Energy Consumption

 Par CUI Engineering

With billions of “things” about to be connected to the Internet, power conservation is critical; not only in self-powered or battery-powered sensors but also in devices such as gateways that are typically powered from the AC line. This article discusses forthcoming Level VI specifications for external AC/DC power adapters, and the design changes needed to meet the new standards and help reduce overall power consumption in IoT applications.

Introduction: The Power Behind the Sensors

The phrase Internet of Things (IoT) conjures up images of pervasive networks comprising tiny sensors, which could be monitoring anything from air or water quality, traffic flow or industrial processes to the environment in our homes or the health of our bodies. The sensors are usually envisioned as ultra-low-power devices capable of operating for a lifetime from a small coin cell or from a solar panel or other miniaturized energy-harvesting subsystem. As such, these devices can be conceived to deliver great operational benefits while imposing minimal environmental impact in terms of their own energy demand.

In a few years, it is estimated that there will be over a trillion connected sensors acting as the eyes, ears and fingertips of the IoT. However, they are unlikely to be connected directly to the Internet. A Wi-Fi or Ethernet connection is simply too expensive and power-hungry to integrate in small, battery- or self-powered IoT endpoints.

In many industrial or domestic sensor-networking applications, connection to the Internet will typically be made through a hub or IoT gateway that provides the bridge between the sensors and the Internet. In this way, the gateway implements non-IP interfaces to the sensors using standards such as Bluetooth Smart or a two-wire connection, and also hosts an Ethernet port or Wi-Fi interface to connect to the Internet. The gateway is capable of transferring data from the sensors to a centralized manager such as a Cloud service, and vice versa, via the Internet. Basic processing of the sensor data will also typically be performed locally in the gateway before the results are passed to the Cloud. Figure 1 outlines the basic functions of an IoT gateway.

Image of IoT gateway is needed

Figure 1: An IoT gateway is needed to connect low-power, non-IP sensors to the Internet.

According to predictions, as many as 50 billion devices such as IoT gateways could be connected to the Internet over the next four to five years. The power needed to manage the diverse gateway functionality, including the multiple sensor interfaces, Internet connection and embedded processing, means the device will need to be plugged into a mains power source, or otherwise recharged frequently. With so many of these devices expected to be added to the Internet in the near future, there could be a significant rise in energy demand, either for offline power or recharging.

Efficiency Standards for Power Supplies

Massive growth in the number of electrical devices connected to the grid is nothing new. The effects have been a major concern of scientists at least since the beginning of today’s consumer electronics age. From the 1970s, when a typical household owned a television and maybe a washing machine, the average number of electronic products per household has risen to twenty-four in the US according to the Consumer Electronics Association. These include multiple televisions, as well as PCs, tablets, smartphones, printers, game consoles and other appliances, which may contain an internal power supply or may run from an adapter or external power supply (EPS). By the 1990s over one billion EPSs were thought to be in use in the US alone.

Image of no-load power draw from external power supplies

Figure 2: In the early 90’s, studies estimated that no-load power draw from external power supplies would account for 30% of the total energy consumed in the US within 20 years if action was not taken.

Knowing that users tend to leave their appliances plugged in even when switched off or disconnected, concern about the “phantom power” or “no-load” power wasted by households began to grow. A 1998 study by Alan Meier of the Lawrence Berkeley National Laboratory (LBNL) in California 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. Subsequently, of course, energy prices have risen and concern has grown over the environmental damage caused by excessive energy consumption.

To combat these problems, the California Energy Commission introduced the world’s first energy-efficiency legislation for external power supplies in 2004. Gradually the majority of world markets, including the entire USA, Canada, Europe, and Australia, followed suit. Ultimately, these various laws became harmonized in the International Energy Efficiency Marking Protocol for external power supplies. This has now evolved through several generations, each imposing successively more 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 Level IV specification of this protocol, and must be labelled with a Roman numeral IV on the nameplate. The EU currently imposes the stricter Level V specification.

The US Department of Energy (DoE) announced in 2014 that all external power supplies manufactured after February 10, 2016 and marketed in the US must meet the higher Level VI efficiency specification. Historical patterns suggest the EU and other authorities will raise their own requirements to Level VI soon after, although none have yet announced their finalized standards.

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. It is important for Original Equipment Manufacturers (OEMs) globally to keep up to date with the latest regulations.

Power Design Choices

Internal power supplies are not subject to the International Efficiency Marking Protocol. Designing-in an internal supply in preference to an EPS may therefore eliminate any need to comply. However, other regulations may apply, such as the ENERGY STAR® rating systems or EU eco-design directive 2009/125/EC for energy-related products (ErP). Moreover, bringing up a custom power supply in-house, or integrating a third-party module, may be outside the designer’s range of experience. An internal supply can also add weight and bulk to the product, thereby requiring a larger enclosure.

An off-the-shelf EPS can provide a fast and easy solution that can be shown to comply with the applicable regulations. CUI began introducing Level VI products to its EPS range in late 2014, to address the coming 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 Specifications

The Level VI protocol is significantly more complex than its predecessors. Five categories are defined. These are:

  • Single-Voltage External AC/DC Power Supplies (basic voltage)
  • Single-Voltage External AC/AC Power Supplies (basic voltage)
  • Single-Voltage External AC/DC Power Supplies (low voltage)
  • Single-Voltage External AC/AC Power Supplies (low voltage)
  • Multiple-Voltage External Power Supplies up to 49 W

Note: low-voltage power supplies have output voltage less than 6 V and output current greater than 550 mA. Basic voltage refers to a power supply that is not a low-voltage power supply. In addition, Level VI introduces the first legislation covering single-voltage power supplies over 250 W.

Compared to the Level V specification for standby power, Level VI reduces the allowable maximum power from 0.3 W (for standard-voltage EPS up to 49 W) to just 0.1 W for single-voltage AC/DC power supplies rated from 1 W - 49 W. The new average efficiency requirements are similarly demanding. Figure 2 illustrates the increase in average efficiency for Level VI basic-voltage AC/DC power supply compared to similar Level III, Level IV and Level V specifications.

Graph of Level VI specification imposes average efficiency thresholds

Figure 3: The Level VI specification imposes average efficiency thresholds higher than those for Levels III to V.

Meeting Level VI by Design

Designing an EPS to meet the new higher standards is a tough challenge. 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. Re-optimized capacitor and resistor values in the secondary feedback circuit 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.

The secondary-side circuitry in low-voltage/high-current Level VI power supplies has been changed from simple diode rectification to synchronous rectification using MOSFETs and an additional control IC. In addition, larger resistance values and changes to other components, such as increased wire gauges, help 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 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.

Conclusion

The IoT promises numerous and wide-ranging benefits to industry, the environment, ecology and quality of life. On the other hand, the massive number of deployments anticipated could introduce significant numbers of new network hubs and gateways that must be powered from the AC line. New external power supplies that meet the latest Level VI marking protocol, which will be mandatory in the US from February 2016, can help to offset the increase in power demand by raising average efficiency and reducing no-load power consumption.

For more information on CUI’s Level VI portfolio at Digi-Key, visit the Level VI Power page.

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