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Distributed power architecture allows for more efficient design structures

The concept of distributed power supply circuits where centralised switched-mode power supplies are combined with a large number of local converter modules enables developers to come up with ever more efficient designs. By using DC/DC converters or switching regulators for the on-board generation of the locally required direct current, the structure of individual assemblies can be significantly simplified. Today, "off-the-shelf" modules are available for virtually any application, and prices have dropped significantly so that bespoke solutions are generally no longer a viable option.

The world of electronics has become a highly digitised world. Micro-controllers, software, sensor technology and network systems – including the famous IoT or Internet of Things – are settings new standards as regards the capabilities of electronic systems. The only field where analog technology has not yet been pushed to the side is the area of power supply.

Switched-mode power supplies have always been the domain of a small number of specialist manufacturers. Given their low voltage ratings, the design of DC/DC converters on the other hand was traditionally considered part of the product development process. These converters were therefore normally designed discretely. At a time when young developers are however no longer particularly versed in analog technology and lack specialist knowledge in the areas of ferrite cores, chokes and transistors, the design of power supplies, including tiny DC/DC converters, should be left to the experts. This approach saves time in prototype development and also helps clarify the responsibilities within the development team.

Distributed power architecture facilitates delegation to experts

As the responsibility for specific assemblies is normally delegated to the relevant specialists within the product development project team, it makes sense to leave the design of the power supplies to the experts. With a centralised power supply that covers the power needs of the entire system, the locally required DC voltages can be generated locally within the assemblies. By adopting such an architecture, the individual development teams remain focused on their actual module design tasks and can work more independently. And there is another advantage: if, down the road, a component in a distributed power system needs to be modified for more power or a different voltage, only the voltage converter of this single component needs to be adapted. The centralised supply and other parts in the circuit remain unaffected.

DC/DC converters contain a toroidal transformer insulating the input from the output, so that the various sectors inside an assembly can be easily separated in order to prevent ground loops and to minimise noise. DC/DC converters can also be used to electrically insulate amplifier channels and to keep interface ports or measuring probes apart from the other electronic components inside the device. This is particularly important in medical electronic devices, where the relevant standards and regulations, including UL/EN60601-1, prescribe extra insulation to protect patients.

Why are modular power supply architectures more efficient?

Every power supply consumes some energy to work properly. With high nominal power ratings, this consumption is however relatively insignificant. That is why a 150W power supply has an efficiency of around 90%, while small supplies with ratings of 1W or 2W barely reach the 70% mark. The efficiency of a good DC/DC converter is somewhere between 85 and 92%, depending on the power class and topology. Switching regulators can however achieve efficiencies of up to 96.5%!

Fig. 2: The R1SX 1W DC/DC converter produced in a fully automated plant has an efficiency rating of 78% under full load.

From the point of view of efficiency, it is therefore preferable to equip a system with one large, centralised power supply, and to generate the various DC powers locally through DC/DC converters and switching regulators.

It stands to reason that "off-the-shelf" DC/DC converters that have been tried and tested in thousands of applications have better efficiency ratings than bespoke devices developed and produced under considerable time pressure. Tests in which the new R1SX-0505 1W converter (fig. 2) the size of a fingernail has been compared with a bespoke converter with an equivalent power rating reveal significant differences as regards efficiency. Under full load, the custom-designed converter reaches 70%, which is a commendable result. At half load, the efficiency drops however to 55%, which is 17 percentage points below that of the R1SX. The power loss in the custom-designed device was 409mW and thus more than double that of the R1SX with 195mW. In this case, switching to an "off-the-shelf" module would not only save energy, but also reduce the head load on the PCB.

 

Fig. 3: Comparison tests with a custom-engineered DC/DC converter (red curve) and the first sample modules of the new R1SX from RECOM (blue curve) show that the "off-the-shelf" module is more efficient, especially in the important medium load range. The R1SX will be available from March 2017.

Efficiency goes beyond electric efficiency rating

When speaking of efficiency, engineers often do not just have electrical efficiency in mind. As the designs of modules become ever more complex, small footprints on the PCB often prove a huge advantage. Today, power density has therefore become an important efficiency factor. Modular converters can normally be packed much more densely than devices of a discrete design, so that "off-the shelf" modules generally take up only half the space on the circuit board. This is of significant advantage, as space tends to be a scarce commodity on PCBs.

Experience shows that the design of the power supplies is generally left until very end of a project. By opting for a modular design with a distributed power architecture, this task can be tackled at a much earlier stage, i.e. the moment the centralised power supply has been defined. Even more time and money can be saved by opting for fully assembled and certified converters, as they make it more likely that the end product passes the EMC tests and the certification procedure at the first attempt. To help customers achieve this, RECOM now offers a special service of preliminary prototype testing at its own EMC lab – and at a very competitive price.

Considering the above, it becomes apparent that a decentralised power architecture is generally the better solution. But what about the costs? Are purchased DC/DC converters and switching regulators not more expensive? When comparing the production costs of internally produced devices and the prices of purchased modules, discretely designed converters tend to be cheaper. A different picture emerges however when the development, testing and certification costs are taken into account. In the not unusual scenario where an internally produced module fails the EMC test or is not approved and certified upon first submission, the initial costs savings might quickly vanish into thin air. The financial loss is even greater, if a redesign leads to a delayed market launch, while competitors are scooping up market shares. Project managers are thus well advised to evaluate carefully whether they want to take the risk associated with in-house development.

Last but not least, good resource management dictates that the number of components and suppliers should be kept to a minimum – which is of course always the case with purchased modules. After all, parts such as toroidal transformers, ferrite cores, cokes and transistors are highly specialised components that are not easily found in the internal parts lists.

Comprehensive product range

Today, developers can choose from a huge range of keenly priced standard power supplies, DC/DC converters and switching regulators. RECOM offers a number of devices that stand out from the competition as they come with advanced features and properties.

The new RAC150-G switched-mode power supply (right) for instance pushes power density to the limit of what is actually physically possible. Measuring 4x2 inches, it is available as an open-frame module or encased in a metal housing. With external cooling, it provides 150W within a temperature range of -20°C to +70°C. The module is available with 12V, 24V or 48V output.

When it comes to DC/DC converters, RECOM impressed the industry with its REM1 series of isolated unregulated DC/DC converters designed for use in electronics for the medical sector (top right). These modules will be available in a SIP7 housing with reinforced insulation up to 4.2kVAC/minute and a 2MOPP/250VAC patient protection rating.

The RxxP22005D series of converters (bottom left) has been specially developed for the supply of SiC MOSFET drivers. They come with isolation up to 6.4KVDC and provide +20 and -5VDC voltage required for the fast and safe switching of SiC MOSFETs.

The R1SX 1W converter described above will shortly get a bigger brother, namely the RTC2. This regulated open-frame module (top centre) is a 2W converter available for inputs of 4.5 to 9V or 18 to 36V and an output of 5V.

The new R420-1.8/PL (124-4230) is a very special device that harvests unused current (<3.5mA) from standardised 4-20mA loops to provide output voltages of between 1.8 and 5V. This unique module powers micro-controllers, HART modems and intelligent sensors directly from the loop.

There are also some interesting additions to our popular range of switching regulators. The new R-78B series (163-394) provides output voltage of 3.3V, 5V, 12V and 15V and currents up to 2A – up to 30W power from a SIP3 housing! Thanks to its high efficiency of up to 96.5%, there is virtually no heat loss, and thus no need for cooling.

All above products come with a 3-year warranty and most of them already comply with the new UL/EN62368-1 standard to come into force in summer 2019

Connector Geek is Dave in real life. After three decades in the industry, Dave still likes talking about connectors almost as much as being a Dad to his two kids. He still loves Lego too. And guitars.
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