IEEE Power Electronics Magazine - September 2015 - 62

White Hot

(continued from p. 64)

loss. While the use of paralleled converters to minimize loss is well known,
keep in mind the extraordinary powerconversion density of these commercial power supplies. It is may be possible to vary the switching frequency of
the high-speed totem pole to minimize
losses when the input current is small.
The same technique can be used
for the dc-dc converter stage of the
power supply. Even with the LLC converter, even if there are no switching
losses, it is a resonant converter, and
there are circulating currents. Paralleling two LLC converter circuits and
only using one at light load can help
reduce losses. For a converter under
PWM control, reducing the switching
frequency at light load reduces losses
and helps keep efficiency high. And
for all kinds of converters, very light
load efficiency is achieved through
"pulse-skipping" techniques that actually shut off the converter for relatively long periods of time, turning

on only long enough to supply a bit of
charge to the output capacitors.
The key to the high power-conversion density is high efficiency and
lower power loss. This allows a design
with small heat sinks (or none at all).
Low power loss also means that very
little empty space is needed for cooling air to flow.
Not long ago, I would have scoffed
if you told me that inexpensive server
power supplies would have efficiencies
of 95% and power-conversion densities
of 40 W/in³. Now that is routine. I have
to wonder, how much better can commercial power supplies be? Can losses
be further reduced by 20-30% to improve the efficiency by another 1%? Can
a server power supply reach 100 W/in³?
Can the cost really be any lower? Given
the improvements of recent years, I
would not bet against it. Write to me at
bob.white@ieee.org and let me know
what you think about how much better
power supplies will be in a few years.

About the Author
Robert V. White (bob.white@ieee.
org) has over 30 years of industry
experience as a power electronics
engineer. He has worked in product
design, systems and applications engineering, and technology development.
He has been an active volunteer with
the IEEE Power Electronics Society,
serving several years on the Administrative Committee, two terms as technical vice president, and as a Chapter
chair. He earned a B.S.E.E. degree
from the Massachusetts Institute of
Technology, and an M.S.E.E. degree
from Worcester Polytechnic Institute;
he is currently pursuing a Ph.D.
degree in power electronics at the
University of Colorado-Boulder. Presently, he is the chief engineer of
Embedded Power Labs, a power electronics consulting company. He is a
Fellow of the IEEE.

Motor Drive Analyzer
Complete Motor Drive System Debug and
Validation in One Instrument

Visit teledynelecroy.com or call 1-800-553-2769
62

IEEE POWER ELECTRONICS MAGAZINE

 September 2015

http://www.teledynelecroy.com

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - September 2015