大多數時候，我們的交流介面卡和電源往往是安靜的，但它意味著什麼，當一個人發出嗚嗚聲？你應該擔心嗎？今天的超級使用者問答帖子回答了一位憂心忡忡的讀者的問題。

今天的問答環節是由SuperUser提供的，SuperUser是Stack Exchange的一個分支，是一個由社群驅動的問答網站分組。

照片由巴特埃弗森（Flickr）提供。

問題

超級使用者讀者Rishat Muhametshin想知道為什麼他的一些交流介面卡和電源會發出嗚嗚聲：

I have many different AC adapters and power supplies for a variety of devices, ranging from **all 5V/1A USB chargers to laptop power adapters and desktop PSUs. However, I often hear a whining noise from some of these power supplies. This happens most often when they are not connected to a device or otherwise in use, and stop making noise when I connect a device that is not fully charged.

Why do some AC adapters and power supplies make this whining noise? Why do some not make this noise? Is there anything that I can do to suppress it?

為什麼一些交流介面卡和電源會發出嗚嗚聲？

答案

超級使用者DragonLord和Daniel R Hicks為我們提供了答案。首先，龍王：

Most power conversion devices contains coils, such as transformers or inductors. These components use electromagneti** to convert AC main power to low-voltage DC power. The varying magnetic fields generated by these components can cause them to physically vibrate at high frequency, resulting in a high-pitched noise.

Most modern AC adapters are switched-mode power supplies. The internal switching frequency of an SMPS is typically low when unloaded and increases with a load (up to a certain point depending on the design). The no-load frequency is often low enough to be within the human hearing range.

In addition, in low or no-load situati*** the PWM (Pulse Width Modulation) used to regulate voltage at the inverter stage will be at a low duty cycle and create a “spikey” output profile which is more prone to causing vibration in coils, and the transformer itself will tend to vibrate as well. Together, these can lead to audible noise especially in cheaper units which fail to suppress this noise.

Under a load, a properly functioning SMPS should operate at a frequency well above the human hearing range, typically 50 KHz or higher (although some older designs operate at 33 kHz). However, the same noise can occur under a load with a poorly designed or defective power supply as the coils may vibrate under electrical stress at a sub-harmonic frequency.

This is why you sometimes see a “glue” of sorts on coils inside electronic devices. The glue helps reduce the vibration and noise the coils generate during normal operation. Of course, this means that a user can apply glue onto coils using a glue gun to suppress coil whine—and yes, people have done this successfully with PC motherboards, graphics cards, and power supplies. However, you generally cannot do this easily on **all wall chargers of the sort you mentioned without risking damage to the charger or exposure to potentially dangerous voltages.

In conclusion, a whining noise is not necessarily a sign of trouble in cheaper wall chargers when they are unloaded. However, a computer PSU or laptop charger that generates coil noise, especially when under a load, may be defective and you may want to c***ider replacing it.

More information on coil noise can be found in this Wikipedia article.

接著是Daniel R Hicks的回答：

A coil of copper wire without any “core” metal plates can be made to whine. As the magnetic field increases and decreases (generally about a thousand times a second), the force of the field causes the dimensi*** of the coil to change slightly, and this vibration leads to a whining sound. Even the wires on a printed circuit board can whine (slightly) under the right circumstances.

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