In many designs selection of components are based on the declared parameters rather than the inherent or parasitic qualities, and in some cases these undesirable qualities do not manifest until another change is made.


In a recent case the client experienced problems with a power-line carrier communication system due to saturation of a common-mode inductor.


In this application the inductor was principally used to suppress noise from a switch-mode power supply and was normally connected in a balanced mode.


The design provided a nominal 100 Ohm impedance at communication frequencies however when the load increased the impedance dropped to 10 Ohm thus significantly attenuating the received communication signal.


No details were available from the manufacturer for the inductor used in this mode. FMA were able to characterise and model  the inductor from the magnetic material B/H curve, core size and winding details.

Case Study 1 – Non-Linear Inductor

Ferrey-Moore Associates

Using this component in a complete model it was possible to simulate the system and to predict the attenuation of the received signal and many other parameters useful in dimensioning the system.


This simulation model was able to determine the performance of the system and possible resonance’s due to interactions with other filters under a wide variety of configuration scenarios.


This was supported from results of practical tests where FMA tested the worst case system configuration which compared favourably with the predictions.


FMA were able to further propose modifications to improve the design, which were implemented and the system is successfully operational and communicating over longer distances than before.

Last updated Thursday, 07 January 2016

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