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Inductors work by storing energy in a magnetic field. As long as the field is changing, the resistance of the inductor will remain high (inductive reactance). My question is: If a strong magnet is placed on the inductor in a switching regulator, why doesnt the external field of the magnet interfere with it's operation? Surely when the inductors field collapses due to current being switched off, the permanent magnet's field will remain, preventing the inductor from generating a back-emf? This is not the case, I tried it and a magnet has no effect.

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  • $\begingroup$ "Surely when the inductors field collapses due to current being switched off, the permanent magnet's field will remain, preventing the inductor from generating a back-emf?" - I do not understand how you came to this conclusion. $\endgroup$ – Alfred Centauri Nov 17 '16 at 21:02
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External magnet close to the inductor will only have effect when it is moving OR inductor core is close to saturation. With the presence of external magnetic field inductor core could saturate sooner (or later - depending on polarity and strength). If the inductor has no core (i.e. air core) it will be indeed extremely challenging to see the effect.

This principle is used in early magnetometers (fluxgate magnetometers).

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    $\begingroup$ Well stated: +1; 1) Clearly, the static magnetic field of a permanent magnet has no current-inducing effect on an inductor unless it is moving, and therefore changing the magnetic field in the inductor. 2) Changing the point on the hysteresis loop of an iron-core magnet, which is non-linear, will have an effect on the inductor's current vs. time curve because of change the saturation of the core. Great answer! $\endgroup$ – Thomas Lee Abshier ND Apr 30 '19 at 17:48

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