CUI’s VP of Marketing, Jeff Schnabel, addresses the truth behind the peak efficiency figures that are used in the advertising of power supplies, and recommends that engineers consider the entire efficiency curve when evaluating performance.
Published by Power Systems Design, the article begins, “It is a well-known fact that engineers do not appreciate being advertised to. In my experience, they tend to prize function over style and want accurate information without attempts to massage the data. This is why the all-mighty datasheet continues to be the primary-source of technical information engineers turn to when evaluating components for their design."
"But here, as in advertising, figures are sometimes cherry-picked to shed the best possible light on a particular component. This practice is done throughout the electronics industry and, in our industry - power supplies – this comes in the form of efficiency figures, typically quoted as the highest point along the efficiency curve of a particular device."
"When peak efficiency is used as a determining factor to select a power supply for a particular application, the design engineer must dig deeper to understand the test conditions used to derive this number; line, load, temperature, and airflow can all affect the stated efficiency. For example, an ac-dc power supply’s efficiency quoted at 230 Vac line voltage may actually operate at levels 6~10% lower if run at 120 Vac. As another example, when a power supply is tested for efficiency immediately at start-up, the number will appear higher than when measured after the unit has reached thermal equilibrium, which in reality is much closer to real world conditions."