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Miniature power supplies for smart homes & smart offices

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The necessary data is collected in real-time by sensors and transmitted to where it is required. These sensors naturally need to be powered from a reliable source. While compact power supplies are the obvious solution, these modules must be chosen carefully, taking into account the special requirements of smart home applications.

Up to a few years ago, only tech-savvy people were able to run a smart home, and the installation of the necessary equipment into existing buildings was a costly affair, involving extensive rewiring and modifications to the existing building structure. Nowadays smart homes can be bought "off the shelf". The entrance of multinational suppliers of IoT (Internet of Things) equipment has revolutionised the market. Today, consumers can choose from a sheer unlimited range of smart devices and solutions designed for easy installation and operation, and prices have come down considerably.

Applications and supply

To provide people with the comfort they seek, smart home devices need to exchange data in real time. The data is thereby collected by numerous sensors that run 24/7 and obviously need to be powered continuously from a reliable source (figure 1). There are a number of options available to do this, depending on the actual application: battery supply, energy harvesting, DC bus supply or direct connection to the power grid. All these options have advantages as well as disadvantages, which cannot be discussed here in detail.

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Fig. 1: Smart homes feature a large number of applications and sensors that need to be reliably powered. Where compact power supplies are used for this, they must meet various, highly specific requirements.

Many smart home applications are battery-powered, as this offers maximum flexibility and does away with the need for a power mains connection. All batteries, however, have a limited service life and need to be replaced at some stage. Given the large number of devices in a home, replacing these batteries in time can become a time-consuming task. Energy harvesting is a promising alternative, but the technology is still in its infancy, and it will likely take some time until practical, reliable and also affordable energy harvesting solutions will be available in the market.

In industrial applications, DIN rail power supplies with a stable 24 V output are the established standard. However, such DC bus systems are not yet a standard feature in office blocks or residential buildings, and their installation is generally very costly.

Much more affordable are compact modules designed to power sensors and other devices. Similar to batteries, they are installed close to the applications, and are powered by the mains.

Requirements for power supplies in smart home applications

Power supplies for installation in smart homes must meet a number of highly specific requirements. Apart from being affordable, they must be extremely compact, as it would otherwise be impossible to integrate them into the devices. In addition, they must withstand frequently changing load conditions, as applications regularly switch between active and idle mode. Given that smart home devices are often in standby mode, their standby power consumption must be as small as possible. Last but not least, they should be fully certified for use in industrial, commercial and home systems, as this greatly facilitates the certification of the end user device.

Compact and well protected

Modern sensors and wireless modules are extremely compact in size – and so are modern power supplies. Only a few years ago, the average size of a 5 W power supply was 2" x 1" (50.8mm x 25.4mm). Today, it has shrunk to 1" x 1" (25.4mm x 25.4mm) (figure 2). Modern power supplies can therefore be easily integrated into extra compact smart home devices. This extraordinarily high power density has been achieved by resorting to primary side regulation (PSR).

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Fig. 2: Smart home applications need compact power supplies that can be easily integrated into sensors and control devices. The picture shows the difference in size between a power supply launched a few years ago and the latest generation of modules available from RECOM. Both units provide 5 W.

Compact power supplies must of course be as safe and reliable as their predecessors. That is why they should come with proper protection against short circuits and overvoltage and also conform to the EMC standards for residential areas. To keep costs low, some manufacturers have excluded integrated EMC filters in their designs. As a result, these filters now need to be incorporated into the actual devices themselves, making them not only bigger but also more expensive.

Fluctuating load conditions are a daily occurrence

Power supplies for smart home applications are exposed to frequently changing load conditions. A GSM module for instance needs up to 2A when sending an SMS or communicating with the base station. When idle, the current consumption is reduced to as little as 1.5mA. This means that the power supply must be able to handle sudden load changes without causing extreme voltage peaks. In this context, the transient behaviour is also an important issue. Most AC/DC data sheets only specify the control mode at load changes from 50% to 75%, which is obviously of little relevance for smart home applications, where changes in the 0 to 25% range are the ones that count. Ideally, the settling time should be 500µs or less.

Typical sensor applications are run in intermittent mode so that they are in energy saving or sleep mode most of the time. For PCB-mounted and integrated power supplies, the European ErP (Energy Related Products) Directives prescribes a standby consumption of less than 500mW. Considering the increasing popularity of smart homes and IoT applications and the huge number of power supplies that will soon be required to power these, this standby consumption is still far too high. Preferably, power supplies should come with a standby consumption of less than half the 500mW limit. Low standby power consumption is however not the only issue. Many IoT and smart home applications are run within an extremely low load range or frequently switch from zero to a low load. Even if the data sheet specifies an excellent zero load consumption, the picture might be very different when there is a low load. This is due to the fact that the controller automatically switches to pulse mode the moment there is a zero load in order to save energy. When even the tiniest load is applied, it switches back to normal operating mode.

Power supplies for smart homes

In conclusion, it is obvious that smart home technology of the future will pose new challenges when it comes to power supplies. Developers therefore need to carefully scrutinise the data sheets of converters they consider for their designs. Otherwise, they might find out too late that the chosen modules do not meet their expectations.

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Fig. 3: RECOM recently launched a new range of compact AC/DC power supplies designed specifically for smart homes and IoT applications.

 

 

 

RECOM offers a broad range of 1-10 W AC/DC power suppliers tailor-made for the specific requirements of smart home and IoT applications. The new RAC-G series has been specifically developed for the efficient and long-term supply of technical building components. Thanks to their high efficiency and low standby loss, they are ideal for energy-saving systems. Apart from internationally recognised safety certificates (EN 60950 and EN 62368), these modules are also certified according to EN 60335 for use in residential buildings.

 

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