Switching power supplies often hum due to a phenomenon related to the magnetic components and high switching frequencies used in these power supplies. Here are the main reasons why switching power supplies can hum:
1. magnetostriction:
Magnetostriction is an effect in which magnetic materials (e.g. iron cores in transformers or coils) expand and contract slightly when a magnetic field is applied. High-frequency magnetic fields are generated in switching power supplies, which can cause this mechanical deformation. When the material vibrates at the frequency of the switching power supply, it generates sound waves in the audible range, which is perceived as a buzzing sound.
2. switching frequencies:
Switching power supplies normally operate at very high switching frequencies, typically in the range of 20 kHz up to several 100 kHz. These frequencies are often above the human hearing range (20 Hz to 20 kHz).
3. load-dependent effects:
In many cases, the switching frequency of the power supply changes depending on the applied load. Under certain load conditions, the power supply can operate in an audible frequency range or generate oscillations that cause a humming noise. Particularly at low loads, switching power supplies can sometimes emit a kind of “squeaking” or “whistling” sound.
In summary, switching power supplies buzz due to vibrations of magnetic components (such as coils and transformers) and mechanical vibrations caused by the high switching frequencies.
This effect is perceived differently from person to person and is not a defect of the product.