Power


Powering the future with intelligence and efficiency


In March 2018 the Applied Power Electronics Conference (APEC) took place in San Antonio (Texas). APEC is the world’s largest convention dedicated to applied power electronics, and the place where research laboratories, universities, market analysts and companies showcase the latest and often ‘industry first’ technologies that make power supplies more efficient, reliable and safer. Patrick Le Fèvre, Powerbox tells us more


T


his year’s event was definitely the real ‘kick-off’ point for the wide bandgap semiconductors and especially the ones based on Gallium Nitride (GaN). It was also a symbolic milestone for a technology called ‘digital power’ that emerged in 2003 as a promising technology. As it was for digital power 15 years ago, GaN started its journey five years ago, and following a similar path is moving gradually from a ‘technical curiosity’ to a ‘commercial product’. Digital power and GaN are both technologies that have been highly debated and challenged when introduced to the market and it is interesting to link both of them in this way, especially when the outcome of combining the best of the two technologies will result in truly outstanding commercial products.


From skepticism to game changer Ten years ago when GaN pioneers presented the concept of industrialising a disruptive technology aimed at offering a more efficient Gallium Nitride based alternative to super-junction MOSFETs, it attracted a lot of opinions and strong statements: “It will never fly!” As it has been for the digital power, the journey from ‘garage development’ to commercial products has been full of frustration, tears and deceptions, though the perseverance and strong beliefs in the technology have brought it to a successful state. GaN high-electron mobility transistors (HEMT) have very interesting intrinsic behaviour patterns, delivering superior switching performance and able to offer unprecedented levels of performance compared to conventional MOSFETs. In terms of intrinsic performance, having a very low charge gate, zero reverse recovery and flat output capacitance, GaN has everything that power designers dreamt of for decades to improve performance, decrease size and to reach the mythical 99.99 per cent efficiency.


One example of a benefit of GaN transistors is the die size, which is much smaller than conventional MOSFETs (Figure 1). The graph compares the normalised area of a chip versus the voltage rating of the best MOSFETs in blue, with the latest generation of GaN FETs. The separation in the die size ‘Figure Of Merit’ between silicon and GaN FETs is growing rapidly. It


30 June 2018


now sits at 16 times at 200V and four times at 100V – and we may not have reached the limits yet. This opens the door for power designers to create higher integration and products that will literally amaze us with their performance levels. So much so in fact, it looks like we have truly entered a game-changing era!


Step by step to maturity As it is for any new technology, especially when disruptive, moving from research to high volume production is a long process, one that includes new learning for electronic engineers and in the case of GaN, the implementation of zero-voltage switching topologies requiring very specific drivers and new ways to control them. Despite the huge benefits of GaN transistors, for many years the lack of drivers has limited the interest level from industrial designers. However the increased number of semiconductor players investing in GaN in the last two years has made this technology simpler to implement.


Many technical barriers have been


removed. Manufacturing processes have gradually been optimised to increase yield and reduce cost, quality processes specific to this technology have been


implemented, and in November 2017 the JEDEC organisation announced the formation of a new committee to set standards for Wide Bandgap Power Semiconductors (JC-70), which is a sign of readiness for mass implementation.


Figure 1: Comparison of the normalised area of a chip versus the voltage rating of the best MOSFETs, in blue, with the latest generation of GaN FET (Source: Efficient Power Conversion (EPC))


Celebrating 15 years of digital innovation Today, digital power is part of most power engineers’ educational programme and is implemented in a large variety of applications. It is important to remember the origins of digital power, and how from early research work conducted in the mid-70s by Trey Burns, N.R. Miller and others, digital power gradually took its place in the power industry to reach a level of maturity that makes total sense for a designer to consider the technology. In the 70s, at a time when the power industry was slowly considering the migration from linear-power to switching- power, Trey Burns researched and explored the use of the State-Trajectory Control Law in Step-up DC/DC converters and he compared two methods of realisation, one employing a digital processor and the other using analogue computational circuits. After more than 40 years from the days of initial research up to APEC 2018, and 15 years from the first commercial digital DC/DC converter presented in 2003, the technology, originally developed for the ICT


industry, is now widely adopted by almost all segments of the industry. From monitoring and controlling deep sea power systems with the highest level of reliability (Figure 2) to guaranteeing stable voltages to critical medical equipment exposed to the high magnetic radiation of a Magneto Resonant Imagery system (Figure 3), digital power is almost everywhere, and soon to be embedded in equipment installed on the International Space Station. For all the pioneers who have been engaged in this journey, this is an amazing situation and we are now seeing the same level of excitement with the development of Gallium Nitride devices.


5000W per cubic inch and 99.99 per


cent efficiency might sound impossible to reach, but who in the mid-70s would have imagined what we could, and have already achieved today when combining new topologies, digital control, new components such as GaN, and of course, the passion to innovate?


www.prbx.com


Figure 2: PRBX VB410-384 - Subsea power supply with full digital control power management, monitoring and intelligent redundancy (Source: PRBX)


Components in Electronics


Figure 3: PRBX GB350 - Coreless power supply operating in high magnetic field applications (MRI) fully digitally controlled and monitored (Source: PRBX)


www.cieonline.co.uk


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