Capacitors & Resistors
smarter electronics New capacitor
technologies for
Feature rich ICs may be at the heart of advanced electronics but improvements in other components, such as resistors and capacitors, are just as critical, as Geoff Imlach explains
A
dvanced electronics lie at the heart of numerous solutions to challenges such as the need for sustainable
energy, safer transportation, smarter buildings, energy-efficient lighting, improved industrial processes and convenient digital living. Accompanying advances in large-scale semiconductor integration, delivering high-performance energy-efficient processors and feature-rich standard ICs, improvements in other components such as power semiconductors, resistors and capacitors are also vital to achieve increased functionality, energy efficiency and system miniaturisation.
Today’s capacitors
Capacitors, as a staple of the electronic designer’s trade, are used to manage energy within circuits to achieve goals such as filtering noise, interfacing between voltage levels, storing energy and enhancing power quality. As end users expect more from their equipment, and as electronic technology reaches into more applications including environments where humans cannot go, increasing demands are placed on these components. Designers are asking for smaller, slimmer devices, with lower parasitic effects, longer lifetimes, higher temperature and voltage ratings, greater stability over time and temperature, and improved high- frequency performance, as well as
16 May 2013
increased energy-storage and discharge capabilities for battery-free energy- harvesting applications and fail-safe power-hold-up circuits. These demands are calling for advances in all types of capacitor technologies, including electrolytic, ceramic, tantalum and polymer-film.
High-voltage, high-power Aluminium electrolytic capacitors are commonly used for power conditioning in a variety of industrial, lighting, consumer- electronics and alternative energy applications. LED lighting and solar or wind-energy applications, in particular, are driving the emergence of compact devices rated for high operating voltages such as 450V or 500V. With derating, these capacitors can be used safely at the voltages applied to large LED-lighting arrays containing many emitters in series. With growing demand for electronic CFL- lamp ballasts, as well as LED drivers, surface-mount high-voltage electrolytic capacitors are being introduced offering long lifetimes of up to 10,000 hours, comparable with the long useful lifetimes of CFL and LED emitters. In alternative-energy applications, rugged electrolytic capacitors are needed for DC/AC inverters used to connect the generator to the grid. In wind turbines, large numbers of high-voltage electrolytic capacitors are used to smooth the voltage
Components in Electronics
on the DC link which feeds the inverter. This network is used to convert the raw turbine-driven AC generator output, which has a variable frequency related to the rotor speed, to the correct frequency and voltage for feed-in to the grid. Capacitors for smoothing the DC-link voltage must be able to handle high ripple currents to withstand load variations and achieve a long lifetime to minimise turbine maintenance overheads. As the concept of distributed renewable energy generation becomes more popular, demand is growing for smaller film capacitors suitable for smoothing duties in micro-generation equipment. C4AE radial film DC-Link capacitors, for example (Figure 1), are optimised for such applications, and have low Equivalent Series Resistance (ESR). This not only helps increase energy efficiency but also reduces
By featuring enhanced film properties, the C4AE series is characterised for operation up to 105°C to meet the requirements of applications such as solar generation, charging Electric-Vehicle (EV) batteries, and industrial power supplies. A combination of several innovations is employed to reduce ESR, including high- conductivity electrolytes, optimised internal geometries and enhanced production processes such as vision-guided welding of terminations.
Figure 1: Miniature DC-link capacitors target low-cost micro-generator applications
internal heating so as to allow simpler thermal management in low-cost equipment for consumer applications.
Small and fail-safe MLCCs Multi-Layer Ceramic Chip Capacitors (MLCCs) are used for a wide range of decoupling, filtering, bypassing and smoothing duties. Typically they offer high capacitance within small case sizes, enabling designers to miniaturise circuit boards and enclosure dimensions. Improvements leading to even smaller case sizes, as well as lower cost and better performance allow these devices to be used increasingly in applications normally served by tantalum, aluminium or film capacitors. Recently unveiled the new high-voltage X7R capacitors feature a proprietary lead- frame technology that allows two MLCCs to be stacked vertically in a single 2220- footprint package (Figure 2), thereby doubling the capacitance in relation to PCB area. These KPS series devices are available with rated voltages of 500 VDC and 630 VDC, and also have low ESR and ESL properties for use in applications such as smoothing circuits in switched-mode power supplies, snubbers in lighting ballasts, and high-voltage coupling and DC-blocking duties in inverters.
Advanced package technology helps combat flex cracking which, historically, has been the dominant failure mechanism among MLCCs. The KPS series features
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