Causes of Inductor Whispering and Inductor Selection

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Causes of Inductor Whispering and Inductor Selection [Copy link]

The problem of inductor howling is often encountered. Normally, the switching frequency of DC-DC is generally 100KHz~2MHz, which is far beyond the audible range of human ears of 20Hz~20KHz. However, when the load is light or the inductor selection is unreasonable, the DC-DC will be in a "frequency reduction" working mode. At this time, the current fluctuation period flowing through the inductor is not 100KHz~2MHz, but the operating frequency at this time is determined by the load size and the internal circuit of the DC-DC chip. When the current frequency flowing through the inductor is in the range of 20~20KHz, we can hear a harsh "hissing" sound.

Inductor howling is the external manifestation of abnormal inductor operation, and the essential cause of howling is vibration. The causes of vibration can be summarized into three types:

(1) Magnetostrictive effect of magnetic core

(2) The magnetization of magnetic cores causes mutual attraction

(3) Leakage flux causes winding vibration

The three pictures above provide a detailed analysis of the fundamental causes of inductor whistle. I will not repeat them here.

Inductors are one of the commonly used components in high-speed circuit design. According to the role of inductors in circuits, there are three main types of inductors:

(1) Filtering

Inductors and capacitors work together to form LC filters or π-type filters. When designing the filter cutoff frequency, it is necessary to pay attention to the problem of self-resonance in the LC circuit. If the frequency of self-resonance is within the filter frequency range, it may cause the ripple after filtering to increase. In addition, the DC resistance of the inductor will cause a certain voltage drop.

(2) Obstruction of current change

The principle of common mode inductance and differential mode inductance is that when current flows through the coil, the magnetic field formed by the inductance hinders the change of current. Since the same-name ends of the common mode inductance are in the same direction, when current flows through, the magnetic field of the inductance coil is enhanced, showing a huge hindering effect on the common mode current.

(3) Passes direct current and blocks alternating current

The inductor impedance is Z=jwL. When the frequency of the AC component of the current passing through the inductor is higher, the inductor's resistance to the current is stronger, and the impedance to the DC current is smaller.

According to their use in functional circuits, they can also be divided into three categories:

(1) RF inductor

(2) Signal inductance

(3) Power inductance

When choosing an inductor, there are four basic parameters to pay attention to:

(1) Inductance value

(2) DC resistance

(3) Self-resonant frequency

(4) Rated current

Among them, the Q value of the inductor is a very important parameter in the self-resonant frequency. The larger the Q value, the smaller the loss of the inductor. In the rated current, pay attention to the two parameters of the inductor: the saturation current and the temperature rise current.

There are two main types of inductor packaging:

(1) Shielded type

(2) Unshielded type

The enameled wires of unshielded inductors are exposed to the outside, and the coils can usually be observed with the naked eye. There is no magnetic shielding cover; the shielded inductor has a magnetic shielding cover on the outside, which has a good EMI effect and can reduce the electromagnetic interference of the inductor to the outside world. In the power supply design of high-speed circuits, shielded inductors are generally selected, and sensitive signals are placed away from the inductor.

秦天qintian0303

This moaning is really annoying.

damiaa

The fundamental cause of howling is vibration

led2015

The magnetic field will cause the interaction force between the coil and the iron core, forming mechanical vibration. It is generally considered to be an unreasonable design.

lanhua

Some people cannot hear above 10KHz; some people can hear above 25KHz, and can even hear the horizontal frequency of a TV. Therefore, you can tell whether the TV is on or not without watching it.