High-Frequency DC-DC Converters: The Writing Is On the Wall

Jan 23, 2007 12:10 PM
By Alan Elbanhawy, Power Semiconductor Industry Veteran

In the past few years, the unprecedented demand for handheld electronic appliances and laptop computers with an ever-more impressive list of features and capabilities has meant more demand for processors. This demand directly translates to greater needs for higher current and power at voltages that will soon approach the fractional voltage range from the dc-dc converters in these appliances.

These demands mean that converters must now be more efficient to allow for longer battery life, while fitting into ever-shrinking volumes and pc-board footprints. And, as if this were not a tough enough challenge for power-supply designers, better transient response and tighter load regulation are also required.

To the experts it is clear that high switching-frequency operation — in the 5-MHz to 10-MHz range — is becoming mandatory. This single parameter holds the key to achieving designs that can meet all the demands of the next generation of portable appliances.

Higher switching frequencies will allow engineers to design supplies with considerably wider control-loop bandwidth, which is typically between a fifth and a tenth of the switching frequency. This is important because the wider the loop bandwidth, the fewer output filter capacitors needed, leading to cheaper design and smaller pc-board footprints. At present, a large number of output capacitors is needed in low switching-frequency applications to properly handle the large and fast transient load currents, while staying within transient voltage regulation limits.

As designs move to high switching frequencies, the filter inductor may also shrink, as less filter inductance is needed. This change further reduces the total volume occupied by the output filter and adds the benefit of lower cost.

The transition to 5-MHz to 10-MHz switching frequencies has been slow in coming due to the demands it places on almost all the components used in the design. Also, there is an immediate need for engineers to learn new processes for designing high current and high frequency converters.

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