Power
Bet on the FET for performance and efficiency
As Nexperia receives a 5* engineer rating for the second edition of its popular FET Application Handbook, Chris Boyce, the company’s product group director, considers the growing importance of these semiconductors and the power engineers who know how to use them
M
odern society faces an unprecedented energy challenge. On the one hand we must meet the demands of a growing population
and the inexorable rise in the number of applications requiring electricity. On the other, there are the imperatives of avoiding a climate emergency by driving down greenhouse gas emissions and reducing reliance on fossil fuels. Power design engineers have a critical role to play in addressing these challenges by finding ways to increase product performance and functionality while constraining power budgets. And one of the ways they can do this is to optimize efficiency through the judicious selection and deployment of the right FET technology.
Power management rises up the design agenda
Today there are almost no applications where power efficiency is not near or at the top of the design agenda. In the case of IoT devices, for example, careful management of power budget can allow some element of data processing to be built into remote nodes. In mobile and consumer products where user experience is all, efficiency means extended time between charge or battery replacement. A similar issue impacts designers of electric vehicles as they seek solutions that eliminate range anxiety, a primary barrier to purchase. Not to mention the fact that the plethora of electronics for safety, comfort and infotainment and the shift to autonomous, connected vehicles necessitates more electronic components than ever before. For data centers, the cost and environmental benefits resulting from the smallest of reductions in energy use across millions of computers makes efficiency a key goal in server design. And with output in kilowatts for motor drives now common, effective use of power has
36 November 2022
become the cornerstone of efficient and accurate factory automation motion control. Minimizing energy use also plays a part in the latest communications developments. The 5G roll-out, in particular, will generate major demand for infrastructure based on high-density, ultra-efficient, ultra-reliable communications equipment.
With efficient power management at the top of the design agenda, the importance of the power engineer is elevated. What’s more, other engineers who have not previously had a power brief are finding they must now broaden their knowledge of power design. This, in turn, demands a comprehensive understanding of components that switch, convert and manage power. Which makes knowing how to evaluate, compare, select and deploy FET technologies an essential skill.
Design challenges
The first hurdle is narrowing down the search to those devices most likely to meet application requirements and comparing them on an ‘apples-to-apples’ basis. With an estimated 20,000 different FETs currently on the market, this is not as easy as it may
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seem. A second complication is that the conditions for which specifications are stated on datasheets vary significantly between suppliers. Being able to interpret datasheets from different manufacturers in the context of a given application’s requirement, therefore, is a critical skill for the engineer tasked with product selection.
Once a shortlist is identified, a detailed
assessment of the effects of factors such as switching, conduction and avalanche losses will be needed. In addition, EMC design considerations demand techniques to reduce switching noise, especially in high-speed applications.
Designing for safety and reliability is important and, in many cases, - in particular those where space is limited - effective heat management is a challenge to consider early on. As well as an understanding of thermal behaviour and packaging implications this also requires some assessment of the impact of the PCB on heat dissipation. Sometimes simulations using RC thermal models, for example, offer a quick and inexpensive way to infer the thermal performance of power MOSFETs using an electrical analogy. When it comes to applications that require small-signal MOSFETs, leakage current will be an important consideration. This is especially true for mobile electronics such as smartphones, tablets, wearables or portable medical equipment where off-state current leakage will influence standby time. Finally, there are other factors to take into account for engineers who are familiar with
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