Column: EMC
magnetic-field coupling with nearby components. Since magnetic field falls off at 1/r (where r is the distance between the two coupling paths), keeping a good distance or using a shield will prevent strong coupling. On a PCB, choosing a shielded inductor
is always a safe option. If possible, the inductors used for filtering purposes should be placed on the quiet side of a PCB. However, this may not always be possible due to design constraints. In a much larger system, such as an
industrial motor drive, inductors should be placed away from other cabling to avoid magnetic-field coupling.
Inductors for electrification Te past decade has witnessed a leap forward in technology and market expansion of the global electric vehicle industry. New automotive products must comply with the new EMC regulations, such as ECE R10, presenting a new challenge for automotive manufacturers. A typical usage of inductors is in
on-board chargers (OBCs) of an electric vehicle, which must comply with the harmonic requirements on the AC power lines. EMI filters are designed for both the input and output stages of the converter. Considering the voltage and current rating of these parts, the OBC filters are not small, so they oſten account for 20- 40% of their form factor. Generally speaking, an inductor is used
for differential-mode noise suppression, whilst a common-mode choke handles common-mode noise suppression. Common-mode noise often has
high-frequency content – from a few MHz to GHz. Due to its high-frequency characteristics, a small value of parasitic capacitance between the converter and ground can provide a low-impedance path for the RF current to form a loop. And since RF current travels on the surface of the cable, which is connected between the converter and the power
Figure 3: General layout rules for inductors
supply unit, the cable becomes a radiating antenna, a big source of unwanted emissions. Te same principle applies to much
larger systems, such as an industrial motor drive, since the motor cables and
the inverter exhibit parasitic capacitance to the ground structure. Common-mode currents thus flow freely through the parasitic capacitance. As a result, a large loop is formed, leading to both conducted and radiated emissions.
www.electronicsworld.com October 2022 11 Figure 2: Shielding the inductor
Figure 1: Basic model of an inductor
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