Accurately measuring efficiency of ultralow-IQ devices

While almost every power-supply engineer intimately knows and understands the lab setup for measuring efficiency, there are many important nuances that must be considered when measuring the efficiency of a device with ultralow quiescent current (IQ). For a device that consumes less than 1 µA, the circuit's currents are very small and difficult to measure. These measurements may equate to calculated light-load efficiencies that are far lower than what is shown in the datasheet graphs and lower than what would be seen in the real application.
This article reviews the basics of measuring efficiency, discusses common mistakes in measuring the light-load efficiency of ultralow-IQ devices, and demonstrates how to overcome them in order to get accurate efficiency measurements.
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