Temperature Impact on Non-Linear Inductors in Operating Conditions for SMPS

The exploitation of power inductors outside their linear region in switching converters requires a detailed description of the magnetization curve that is often not included in the datasheets; besides, the temperature of the inductor must be taken into account. This paper shows how to characterize the behavior of an inductor when it is operated up to saturation and its temperature rises. In order to characterize the inductor in real operating conditions, a dedicated measurement rig has been developed. It consists of a switching converter that includes the inductor under test and is controlled by a virtual instrument developed in LabVIEW. The characterization system was tested by retrieving the inductance and the magnetization curves vs. current for two commercial inductors at core temperatures up to 105°C. The magnetic core is then characterized by the saturation current versus inductance, obtaining an expression for the whole family of inductor sharing the same core. Finally, we analyzed experimentally the thermal transient of the inductors in operating conditions confirming the fundamental role of temperature in changing the current profiles and the core saturation condition.