Power Supply Design
Efficiency Challenge 2004, Best in Class C2, Open Category.
Round dots mark the winning entries in each class. The
magenta trendline is a fit to the data of the "open-class" winners.
The Hong Kong Polytechnic University entry won the "Grand Champion"
award for beating the 54% minimum efficiency for class A (up to
2.5 W) by a huge margin. The Dartmouth entry also stands out as
being well above the trendline.
Our Design Approach
- Efficient Magnetics.
In most power supplies, the magnetic components—transformers and
inductors—are responsible for the largest fraction of the loss.
Our approach was to accurately model all the losses in the main
high-frequency transformer, and to optimize the design to minimize
losses. The transformer uses litz wire to achieve very low winding
losses. Litz wire requires careful design—it can make losses
worse if it's not used carefully. We used the LitzOpt program,
available for free download or use online on our software page.
LitzOpt provides the user with a wide range of design options with
different cost/loss tradeoffs. To enter in the “open
class” competition, we of course selected a high-cost, low-loss
design, but the software also provides other options with slightly
higher loss at much lower cost.
- Conventional Topology.
The circuit is a flyback converter—a standard circuit. Using a
single conversion step helps minimize losses.
- Attention to Details.
Every section of a power supply—indeed virtually every
component—dissipates some power. Thus, it can be important to
consider efficiency in every design decision. Although our design
included many careful choices, and some innovations such as a
low-power synchronous rectifier control circuit on the input, time
constraints prevented us from implementing all the improvements that
are possible using only well-known techniques. Thus, we believe that
substantially higher efficiency is feasible.
Design team members:
- Jennifer D. Pollock, Project Leader, PhD Candidate
- Xi Nan, PhD Candidate
- Magdalena Dale, MS Student
- Satish Prabhakaran, PhD Candidate
- Charles R. Sullivan, Associate Professor
For comments or questions e-mail: Charles.R.Sullivan@dartmouth.edu.
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