What is the reason for inductance whistling?

The frequency of the sound that can be heard by the human ear is between 20Hz and 200Hz. If an inductance howls, it can be confirmed that the switching excitation current frequency at both ends of the inductance is around 20Hz to 20KHZ.

One of the reasons for inductance howling is that the inductance is not fixed, resulting in cavity noise. When the current passes through the inductor, the magnetic field generated by the inductor coil will cause the coil position to move. When the current disappears, the position will be restored. If the inductance coil is not fixed and there is a switch excitation current frequency between 20Hz-200Hz, the inductance coil may vibrate and compress the surrounding air due to cyclic position changes, which can easily form audible cavity noise, namely inductance whistling.

Sometimes the switching frequency is not between 20HZ-20KHZ, and there may also be inductance whistling. The reason is that the load is unstable, and a more common one is the power inductor howling in DC-DC circuits.

The reason for the power inductance of DC-DC circuit whistling is that the load current is too large. At this time, the power inductance has been saturated, the inductance value becomes smaller, and the charge and discharge current speed of the inductance rapidly increases. The internal current limiting protection circuit will immediately adjust the duty cycle of the DAC internal switch, or immediately stop the switch operation until the detection current is within the standard range, and then resume the normal working switch, while the stop and resume Switching frequency is exactly between 20Hz and 200Hz, So there is an inductance howling.

Another reason for the howling of the inductor is the occurrence of magnetostriction in the magnetic core, and the frequency range of the current ripple that drives the magnetostriction of the inductor core is precisely around 20HZ-20KHZ.

How to solve the problem of inductance whistling?
How can we solve the cause of the above inductance whistling? Here are four solutions to teach you:
Method 1: After immersing the inductor in the adhesive, use a vacuum box to empty the bubbles inside the adhesive to fix the coil and solve the problem of inductance howling caused by the unstable inductance (PS: it is better to use epoxy resin hard sealing material for immersing the adhesive)
Method 2: Reducing the load current can solve the problem of inductance whistling. 3
Method 3: Starting from the switch duty cycle, stabilizing the DC-DC switch duty cycle can fundamentally solve the problem of inductance whistling
Method 4: Replace the howling inductor with a higher saturated power inductor or a slightly higher power DC-DC chip