Influence of DC Bias on the Electrical Characteristics of SMD Inductors

Abstract

As the dc bias flows through a ferrite chip surface mount device (SMD) inductor, it tends to premagnetize the core and reduce its inductance and impedance. It is observed that this drop is especially emphasized when the dc current exceeds the safety limit given by the manufacturer. Therefore, it is necessary to investigate and predict the degree of electrical characteristics degradation as well as the dependence of the core losses on core temperature. In this paper, a measurement technique for the investigation of the influence of dc bias on the electrical characteristics of SMD inductors (i.e., inductance, resistance, Q factor, and real and imaginary part of impedance) for printed circuit board applications is presented. Analysis is based on the model of the SMD inductor, which can be presented as a two-port equivalent circuit with intrinsic and extrinsic parameters. For calculation of the parameters of the SMD inductor, extracted from measured S-parameters using vector network analyzer, the in-house software tool IndCalc was used.

International Journal of Electronics and Telecommunications

“…However, there are several research papers and application notes demonstrating measurements of capacitor impedance, parameters of inductors and complex magnetic permeability of magnetic core materials by using VNAs [3] - [7]. Despite the fact that a technique that can be used with VNAs to measure parameters of DC biased inductors was proposed in [7], effectiveness of the technique for DC biased inductors impedance measurements was not sufficiently shown because accuracy of the technique over wide frequency range was not analyzed. Moreover the technique proposed in [7] relied on the use of a VNA with special softwarea test fixture simulator.…”

“…Despite the fact that a technique that can be used with VNAs to measure parameters of DC biased inductors was proposed in [7], effectiveness of the technique for DC biased inductors impedance measurements was not sufficiently shown because accuracy of the technique over wide frequency range was not analyzed. Moreover the technique proposed in [7] relied on the use of a VNA with special softwarea test fixture simulator. The main original contribution of this paper is analysis of applicability of a typical VNA (without test fixture simulator or other dedicated software) for measuring impedance and inductance of DC-biased inductors.…”