Power System DesignSponsored by: CELESTICA CORP.

April 12, 2004

Select The Optimal Power Capacitors For The Load

With system voltages dropping, load currents rising, and clock rates increasing, effective power management is now crucial to system performance. Consider, for example, the integration of dc-dc converters that mount on pc boards along with their associated system circuits. Converter manufacturers cannot know every application beforehand, so they design converter circuits for typical loads. To optimize an application, the designer must add capacitors between the converter and the specific load (Fig. 1).

Optimizing the converter-load interface requires knowledge of both the converter and its load. Critical converter characteristics include its bandwidth, output current slew rate, and output impedance. These parameters determine its ability to respond to rapid load changes. Important load characteristics include the system clock rate, the type of load changes to expect, and the allowable voltage deviation due to load transients. Also, system layout affects power delivery because the pc-board's parasitic resistance and inductance result from the power and ground planes located between the converter and its load.

One solution to this system problem is placing capacitors across the load that act as reservoirs to supply charge during a step load, and absorb charge during a step unload until the converter can respond. The optimum solution is to determine the capacitor configuration that provides the required performance at the lowest cost and the smallest physical size.

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About the Author

Sam Davis 2

Sam Davis was the editor-in-chief of Power Electronics Technology magazine and website that is now part of Electronic Design. He has 18 years experience in electronic engineering design and management, six years in public relations and 25 years as a trade press editor. He holds a BSEE from Case-Western Reserve University, and did graduate work at the same school and UCLA. Sam was the editor for PCIM, the predecessor to Power Electronics Technology, from 1984 to 2004. His engineering experience includes circuit and system design for Litton Systems, Bunker-Ramo, Rocketdyne, and Clevite Corporation. Design tasks included analog circuits, display systems, power supplies, underwater ordnance systems, and test systems. He also served as a program manager for a Litton Systems Navy program.

Sam is the author of Computer Data Displays, a book published by Prentice-Hall in the U.S. and Japan in 1969. He also authored the book Managing Electric Vehicle Power. He is also a recipient of the Jesse Neal Award for trade press editorial excellence, and has one patent for naval ship construction that simplifies electronic system integration.

You can also check out additional articles on his other author page.