Over the last decade, notebook computers have become commonplace household and business gadgets: everyone from business travelers to weekend warriors understands the importance of battery life and the frustration of dealing with drained laptop batteries. Alan Elbanhawy, a power systems industry expert, decided to investigate ways to optimize battery life in notebook computers. At the time, he was working with a major semiconductor manufacturer making Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETs), power switching devices used in synchronous buck dc-dc converters for computers. With computers using in excess of 500 million converters each year, this is one of the most popular topologies in the power industry. To maximize battery life, it is important that these converters are as efficient as possible. Elbanhawy realized the importance of better understanding the power losses inherent in these devices to enable engineers to refine their design process, save energy, and at the same time, help the environment.
Determined to find a solution, Elbanhawy worked with the popular engineering and mathematics software Maple from Maplesoft. Using Maple, he developed three applications dealing in great depth with power loss mechanisms in these converters. Maple, essential technical computing software for engineers and scientists, provides all of the necessary technology, whether an engineer needs to do quick calculations, develop design sheets or produce sophisticated high-fidelity simulation models.
Elbanhawy first derived frequency-dependent power loss equations that were much more accurate than those in the traditional engineer's toolkit, an extremely challenging problem that would have been very difficult without Maple. He determined that the error involved in calculating the conduction losses using the traditional equations could be as large as 200 percent!
Cross conduction refers to the condition where both MOSFETs in the synchronous buck converter are turned on at the same time. This condition can result in extremely high current flow, greater losses and lower power conversion efficiency. However, if the devices are chosen appropriately, cross conduction can be reduced or eliminated. With Maple, Elbanhawy could easily visualize the various ranges at which cross conduction occurs, and developed mathematical formulas allowing designers to test the suitability of various MOSFETs for use in these converters.
Finally, using Maple's powerful mathematics and visualization tools, he explored the effects of the source inductance present in today's most common MOSFET packages, and discovered why measured switching losses have always been higher than those calculated by textbook equations. He determined that to improve converter performance, it is necessary to improve package and printed circuit board layout techniques.
Based on this research, new MOSFET packages have been developed by several manufacturers to address the power loss problems, and these new methods have been incorporated widely in the industry in North America, Europe and Asia Pacific. Engineers now have a much better understanding of the various loss mechanisms, and have incorporated the results as an inherent part of the design process.
Not only did Maple enable this deep, math-intensive research, but by using Maple to create the actual research paper, several advantages were provided. Using Maple, it was easy to include the full derivation of equations in Elbanhawy's papers to help readers understand the thought process behind the research. Maple's strong visualization capabilities are indispensable in understanding the subject matter: Several 2-D and 3-D graphs clearly illustrate the intermediate and final results. Most importantly, because math in a Maple document is live, readers can take a deeper look at the results: They can interact with the document, draw different graphs, view graphs at any angle, and examine the concepts as they apply to their existing or in-development designs.
Elbanhawy says he is excited about Maple's contribution to make his research possible. "I would never have endeavored to do all of this math-intensive work without Maple," he says. "With Maple, I can write the equations and within minutes I have the solution and any verification I need. I can then plot it and investigate the interdependencies of the different device parameters. Without Maple, one mistake along the process and you are back to the drawing board!"