Challenges and solutions in measuring computer power supply efficiency for 80 PLUS® certification

This paper discusses the techniques, challenges, and results of measuring computer power supply (CPS) efficiency, power factor (PF), and input harmonic currents for the 80 PLUS® program since its beginning in 2002. To date, over 750 power supplies have been tested with many certified for the 80 PLUS® program. In spite of the large number of power supplies tested and years of testing, there is uncertainty within the computer power supply industry about the correct method for measuring efficiency, power factor, and harmonics. Moreover, in order to improve efficiency at light loading, manufacturers are adopting a duty-cycle control approach to power factor correction that raises even more questions on the proper measurement techniques. This paper presents detailed results of years of computer power supply testing, provides a detailed technical analysis on measurement accuracy with background on why specific measurement techniques were adopted, and looks to the future on upcoming technical difficulties and offers solutions for overcoming these difficulties.