Methods for eliminating inductor acoustic noise, monolithic molded inductors

2023-04-24 10:29

Methods for Eliminating Inductor Whine 1pim Integrated Molded Inductors and Wound Chip Inductors Causes of Inductor Whine At its core, sound is a type of noise caused by vibration.

Methods for Eliminating Inductor Buzzing

1pim integrated molded inductor, wire-wound chip inductor

Causes of Inductor Whine

The essence of sound is noise, caused by vibrations.

PIM integrated molded inductor, T-core process ferrite magnetic core

1. When an inductor is operating, current flows through the coil. Because the currents in adjacent turns are in the same direction, the resulting magnetic fields repel each other, causing the coil to shift. Once the current ceases, the coil returns to its original position, but this sudden movement can induce vibrations and oscillations, leading to a whining or buzzing noise.

2. Instability in the load causes overlapping frequency bands during the switching power supply’s self-regulation, resulting in howling.

3 At low frequencies, inductors generally store energy and also exhibit high-frequency filtering characteristics.

However, at high frequencies, its impedance characteristics become quite pronounced. In particular, once the operating frequency exceeds the resonant frequency, the inductance initially increases; but after reaching a certain frequency, it suddenly drops sharply, leading to oscillation or whining noise.

2. Elimination of Inductor Buzzing

2.1 Changing the Switching Power Supply Frequency

If you hear inductor whine, try adjusting the switching frequency by setting it above the audible range (20 Hz to 20 kHz) to reduce noise. Alternatively, you can lower the load current or replace the DC‑DC converter with one that has a slightly higher power rating to address excessive load current.

2.2 Inductors on the Fixed Circuit Board

If the inductor coil is not securely fixed, it can also cause inductor whine. You can apply liquid clear varnish or RTV silicone sealant to the inductor coil.

2.3 Use of Ferrite Cores

When magnetic energy is stored in the air gap of an inductor coil, vibrations occur, generating noise.

Consider switching to a ferrite core. Ferrite cores are primarily composed of three metallic elements—iron (Fe), manganese (Mn), and zinc (Zn)—and are commonly referred to as manganese–zinc ferrites. Toroidal ferrite cores, lacking an air gap and featuring a uniform cross-sectional area, exhibit exceptionally high magnetic performance.

Reliability Testing of Inductance Values for Monolithic Inductors

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