Switching power supplies, as devices, can sometimes produce noise. But why do switching power supplies generate audible noise, and how can it be addressed?
Why do switching power supplies produce audio noise?
The audible audio noise of a switching power supply is inseparable from the transmission of sound waves, and therefore its noise transmission is also inseparable from vibration. In electronic circuits, component vibrations fall into two main categories: one is the vibration or collision of internal materials caused by changes in the voltage or current flowing through a single component, generating sound waves; the other is the vibration or collision caused between unit circuits or multiple components. For example, vibration circuits or components with loosely connected structures. Here's a question: if components such as transformers, inductors, ceramic capacitors, and MLCC capacitors were connected like transistors, would there still be noise? Theoretically, if the components were seamless, and the alternating energy of the vibration circuit itself could not cause collisions, the switching power supply would have no audible audio sound.
In practical circuits, if a vibrating circuit or alternating signal can cause vibrations within a component, then sound waves will be generated. If these sound waves are within the range of human judgment and have a sufficiently large amplitude, then we can hear them. In practical applications, transformers, inductors, ceramic capacitors, and polyester film capacitors vibrate due to alternating current or voltage, ultimately resulting in audible audio noise in the switching power supply.
II. How should we deal with audio noise?
1. Increase the tight bonding of different components and structures of components. For example, oil immersion, glue application, vacuuming, etc. of transformers and inductors are all ways to effectively bond different materials.
2. To reduce the disturbance caused by alternating current or prevent disturbances that can be heard by the human ear, IC designers should try to avoid controlling the IC to operate in the frequency range that the human ear is sensitive to. User engineers should do a good job of debugging and stabilizing the feedback loop to prevent the occurrence of positive feedback loops in the audio range.
3. Considering the current frequencies of switching power supplies, 45K, 65K, 100K, and 200K are unlikely to prevent sounds audible to the human ear. This is a carrier wave issue; the low-frequency waveform is transmitted through a high-frequency carrier wave, forming another low-frequency waveform, ultimately leading to audio noise. Adjusting appropriate feedback parameters can prevent the transmission of low-frequency carrier waves.
