High-Frequency DC-DC Converters: The Writing Is On the Wall
Jan 23, 2007 12:10 PM
By Alan Elbanhawy, Power Semiconductor Industry Veteran
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For starters, if we really want to reap the full benefits of the high frequency approach, ceramic capacitors used in the output filter must be chosen to handle larger ripple currents for a given value and package at a lower effective series resistance for reduced output-ripple voltage. A variety of small-outline, low-profile, surface-mounted inductors are currently available for designs in the megahertz range and in the right inductance range of 30 nH to 100 nH. But some further reduction in size is still needed for currents in the neighborhood of 5 A to 10 A and even beyond to address the developing needs for the not-so-distant future.
This brings us to the switching power MOSFETs needed in these applications with their two ingredients, namely package and silicon technology. High frequency-power packages have matured in the last few years, and several packages are already available and can be used once this trend comes to fruition, becoming common practice.
Power-switching devices like MOSFETs that are used in these applications must offer low enough switching and conduction losses to achieve total power efficiencies of 85% to 95% at full current. At the same time, the control scheme must be designed to offer similar efficiencies across almost the entire range of load current to maximize the battery life. The demands on the power train create opportunities for the engineering community to develop the present topologies and/or invent new topologies and smarter gate drivers to deliver the performance levels needed.
In my opinion, the best approach would be “complete power modules” that are comprised of the controller, gate driver and switching devices where all the interfaces have been optimized to deliver the highest possible performance for a given application. Few such modules are available today from a small number of suppliers. Nevertheless, these modules open the door for further development to improve dc-dc converter performance in the portable and handheld market.
