Q&A(FAQ) Why does audible noise occur with pulse load?
1. Cause of the sound
The pulsed load, such as a motor or an indicator, may generate audible noise. In most cases, when the frequency of the pulse load falls within the audio range (a few kHz up to around 20 kHz), sound may be produced. The component primarily responsible for this noise is the choke coil. Vibrations of the coil’s core, caused by the magnetic field generated by the pulse current, are what produce the sound.
The mechanism can be explained as follows: when current flows through a magnetic material, such as the core, the material becomes magnetized. If the current changes, magnetostriction occurs, which is a phenomenon in which the magnetic material expands and contracts. These rapid expansions and contractions cause the surrounding air to vibrate, producing sound. This is a normal property of magnetic materials and does not result in any damage, such as nicks, cracks, or changes in magnetic characteristics. Therefore, the electrical performance of the component is not affected.
2. Solution
Even if audible noise is emitted from the power supply, it does not affect its electrical characteristics.
Furthermore, the noise can be reduced by installing an external LC filter at the output of the power supply.