Front-end AC-DC power components help engineers meet key metrics

24 June 2015

Power system engineers are required to meet a range of system requirements that are typically efficiency, density or flexibility.

A new AC-DC front end allows engineers to use the Power Component Design Methodology to meet the demands of their application. 

Although Moore’s law means that the electronics industry frequently sees dramatic improvements in performance and functionality, most of these are incremental improvements: a better way of doing the same things. The latest embedded RISC processors, for example, would be familiar to engineers 30 years ago, even if the performance would be astounding. Power system design, however, is different: the approach to developing power systems has changed radically as engineers take advantage of different power architectures. These changes have been driven by the introduction of new technology, which both changes the requirements of the load and enables new power components to be developed.

Initially power systems used a Centralised Power Architecture (CPA): an approach where a single power supply generates all the voltage rails that a system requires. Whilst simple in concept, CPA systems cannot efficiently deliver the high current, low voltage power that semiconductors such as processors and FPGAs began to demand due to the I2R losses in the long cabling.

In the early 1980s, Vicor introduced the Brick, an easy-to-use power building block that could be placed nearer the load. Engineers quickly migrated to a Distributed Power Architecture (DPA), where power was distributed at a higher voltage and then converted close to the load, reducing the impact of losses in the power rails.

Whilst distributed power was a dramatic step forward, the rapid development of semiconductor technology mean that power system developers were being asked to provide an increasing number of rails at different voltages, requiring several Bricks to be used, which took up valuable real estate. Furthermore, modern loads often required fast response to changes in current demand, something that the DPA was sometimes unable to deliver.

Engineers evolved the DPA into an Intermediate Bus Architecture (IBA). In this approach a semi-regulated bus, which is typically 48 V, is used to distribute power to Intermediate Bus Converters (IBCs) that provide regulation, transformation and isolation. The IBCs provide a lower voltage to Point-of-Load converters (PoLs), which are smaller devices that can be located very close to the load. 

Today power engineers need to meet three conflicting demands: increase power system efficiency, reduce the space required by the power system and ensure that designs are flexible and can be changed quickly to adapt to changes in the requirements of the loads. To achieve this they are adopting a new approach termed Power Component Design Methodology by Vicor, a technique that uses smaller building blocks called power components.

Power components separate the functionality required in a typical power chain into small, flexible building blocks. For example a Bus Converter Module (BCM) provides isolation and transformation, a Pre-Regulator Module (PRM) provides just regulation and a DC-DC Converter Module (DCM) integrates isolation, transformation and light regulation into a single component. 

High-performance power components must blend the right level of integration, functionality and output power. With the power density often constrained by the ability to remove heat from the component, packaging is a critical determinant of overall performance. The package must remove heat from the internal electronics, be easy to mount so that heat can be removed from the package itself and it must be a robust and rugged design that can withstand the environments in which the component will be used.

Each power component has been optimised for efficiency and power density, and the approach is inherently flexible – a change in requirements, for example the current or voltage to a particular load, can often be accommodated by simply changing one of the components.

In the past there have been a limited number of front-end power components, particularly AC-DC converters that offer flexibility, performance and ease-of-use. VIA PFMs address this need, allowing complete AC to Point-of-Load systems to be designed using Power Component Design Methodology.

The VIA PFM family offers a universal AC input (85 – 264 Vac with frequencies of 47 to 63 Hz) and provide either a 24 V (PFA175x240x400Axx) or 48 V (PFA175x480x400Axx) isolated, regulated output at 400 W. Unlike some other AC-DC converters, VIA PFMs maintain maximum output power over the entire AC input voltage range.

In addition to providing isolation, voltage transformation and regulation, these power components also include features to make architecting power chains easier. Active PFC (Power Factor Correction); EMI filtering; transient surge & inrush protection; as well as voltage, current and temperature protection are all integrated, simplifying the challenge of meeting regulatory standards and ensuring that systems built using the component are robust and reliable. VIA components also integrated directly with other Vicor power components, including PoL regulators and DC-DC converters.

As a power component, the VIA PFM is not a complete AC-DC power supply, but engineers only need to add a rectifier, fuse, MOV (metal-oxide varistor) and hold-up capacitors to build a complete AC to 48 V or 24 V supply.

The VIA PFMs are one of the first power components to be built using Vicor’s VIA packaging technology, which was developed specifically for high-performance front-end power components. Its highly-efficient double-sided thermal housing removes heat from the top and bottom of the components within the VIA package, but requires heat sinking on only one side, optimizing the removal of heat while simplifying the thermal design. The compact form-factor allows VIA devices to be mounted on their side in 1U cases, while the chassis-mount version allows the system chassis to be part of the thermal design. In industrial applications it is even possible to mount the VIA components behind DIN rails, meaning that they effectively require no additional space within the system.

The first products built using VIA packaging technology are the AC-DC VIA PFMs and a VIA BCM, an HVDC (high voltage DC) front-end. This platform, however, can be applied to Vicor’s current and future power-conversion topologies. 

VIA PFM enables users of Power Component Design Methodology to create power chains from AC to PoL. Engineers can now use this building block approach to create flexible, efficient and dense high-performance power systems quickly and easily. With an online suite of power system design tools, PowerBench, which allows engineers to move quickly from a specification for inputs and outputs to analysing the performance of a power chain using the Vicor Whiteboard, even designers who are not power specialists can use the methodology to create power chains for complex and demanding applications.

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