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 varying magnetic fields generated by these components can cause them to physically vibrate at high frequency, resulting in a high-pitched noise. These components use electromagnetism to convert AC main power to low-voltage DC power. 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. However, I often hear a whining noise from some of these power supplies.
Laptop Makes High Pitched Noise By jachohewcimb1981 Follow | Public
