Characterization of inductors in partial saturation for SMPS applications

Giuseppe Lullo, Gianpaolo Vitale

Risultato della ricerca: Conference contribution

Abstract

The exploitation of partially saturated inductors in Switching Mode Power Supply (SMPS) isa key strategy for reducing the size of SMPS and increasing their power density [1]. Howeveran accurate characterization and modellization of each inductor is needed for a correct designand control of the SMPS [2]. Most of inductors’ datasheets only indicate the nominalinductance at low current. Anyway, when the inductor is subjected to a higher current, thevalue of the inductance is lessened. Moreover, inductance meters often actuate theirmeasurements at no or moderate DC bias. In this work we describe the realization of anautomated test bench (Fig. 1) for characterizing an inductor under variable current levels,moving its operating point form the linear region to the partial saturation region [3].The core of the measurement setup is a simple buck converter, used for applying a squarewave voltage to the inductor under test (Fig. 1). The current flowing through the inductor ismeasured by a Hall-effect current transducer. In order to measure the inductance at differentvalues of the DC bias current, a constant current sink is placed after the LC filter as a variableload. The measurement is carried out by exploiting the inductor constitutive equationVL = L dIL/dt , rewritten as: L = VL / (dIL/dt). For small current variations, the value of L canbe considered constant and depending only on the average current. The DC bias current, thefrequency and duty-cycle of the switching element can be controlled by a virtual instrumentdeveloped in LabVIEW, which also takes care of data acquisition and post elaboration(Fig.2).Several inductors have been tested using the described setup. Figure 3 shows a typical plot ofthe inductance L versus the inductor current IL . The inductor under test has a rated value of470 μH. The partial saturation of the inductor is quite evident. Reproducibility tests have beenperformed on the system, by comparing the results of several measurements on the sameinductor. Standard deviation bars, indicated in the plot, show the acceptable precision of themethod, the results being well within 1%. The absolute accuracy has not been tested due tothe lack of calibrated reference inductors, however the inductance values measured at lowcurrents are in good agreement with nominal values.
Lingua originaleEnglish
Titolo della pubblicazione ospiteBook of Abstract of the 49th Annual Meeting of the Associazione Società Italiana di Elettronica (SIE2017)
Pagine154-155
Numero di pagine2
Stato di pubblicazionePublished - 2017

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