Energy Generation and Conversion for Portable Electronic Systems

  • Naehyuck Chang


Portable computing and communication devices such as cellular phones, PDAs, MP3 players, and laptop computers are now being used as essential devices in our daily life. The operational lifetime of these devices is determined by the capacity of the energy source, usually a battery. The capacity of a battery is proportional to its volume and weight; however, portability places very stringent constraints on its size, weight, and form factor. Unfortunately, improvements in the energy density of batteries have lagged far behind the increasing energy demand of many portable microelectronic systems. This widening gap between the capabilities of batteries (energy source) and the demands of the processor and peripherals (energy consumers) is one of the primary challenges in the design of portable systems. Obviously, this gap can be reduced by either improving the energy efficiency of the consumer (performance per watt) or by increasing the energy density of the producer.

The ultimate goal of low-power design is holistic optimization of the system-wide power consumption. Most of the low-power research literature deals with minimization of power consumption of the energy consumers, e.g., microprocessors, memory devices, buses, and peripheral devices, as the primary issue in low-power design. However, efficient power conversion and delivery is equally important for the energy efficiency of the whole system.

Currently, there exists a large body of literature on improving the efficiency of the energy consumers, that is, processors and peripherals. For processors, the basic techniques involve dynamic voltage and frequency scaling (DVFS); for subsystems such as disk drives and other peripherals, the methods involve various forms of speed control, and are generally referred to as dynamic power management. Nevertheless, power consumption still continues to plague the industry because of the continuing increase in leakage current, and dynamic power consumption is also growing as computational demand continues to increase.

Due to discrepancies in device technologies, I/O interface, nondigital elements, and so on, each device requires different supply voltages. Some analog devices require very low ripple power supplies. Consequently, many different types of voltage regulators are used in a system. DC–DC converters and linear regulators cannot exhibit an acceptable conversion efficiency at all times, so enhancement of power conversion efficiency is crucial in leveraging the efficiency of the entire system.

In general, 20% to 30% power reduction of a target component is not easily achievable. In addition, even a dominant power-consuming component occupies around 10% of the whole system power consumption. As a result, a 30% power savings from a component achieves 3% extended battery life of the target system. However, power generation and conversion efficiency directly impacts the power of the whole system. Recovering 10% of the power conversion and generation provides an actual 10% battery life extension.

This chapter introduces power conversion subsystems and their efficiency characteristics followed by system-level solution to leverage the power conversion efficiency. The subtopics include:
  • Power sources and energy storage devices

  • DC–DC conversion and efficiency

  • Applications of power source-aware power consumption


Sensor Node Supply Voltage Power Conversion Efficiency Pulse Width Modulation Switching Regulator 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  1. 1.Seoul National UniversitySeoulRepublic of Korea

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