On Measuring Power Efficiency in DC-DC Converters at Light Load Currents

This paper tackles the problematic issue of measuring the efficiency at DC-DC converters operating in PFM mode, which are used for light loads such as sensor nodes. Such converters present a pulsed input current, which hinders a correct estimation of the average input power. For estimating it, two instruments were used (a power analyzer and a current waveform analyzer) as well as two methods respectively based on the following calculations: 1) exact from the voltage and current samples and 2) approximate from the average values of voltage and current. Tests were performed on a commercial boost converter (TPS61020). With both instruments, the first method provided correct values for the efficiency whereas the second, which is the most commonly used, underestimated the efficiency by a 3 % and 1.5 % for load currents of 10 mA and 70 mA, respectively. Just adding an input capacitor of 100 µF solved that problem. The use of this capacitor was also beneficial for the first method when using the power analyzer since it reduced the instrument uncertainty.