What is the reason for inductance ↑γ← whistling?

The frequency of the s×÷←ound that can be heard ₩§↕∞by the human ear is between 20Hz and ×→ 200Hz. If an inductance howls, i←₹t can be confirmed that tα ∞he switching excitati©₽≠Ωon current frequency at both en₹★∑ds of the inductance ←♦λ→is around 20Hz to 20KHZ.

One of the reasons fo¥‌∏r inductance howling is t♥≤hat the inductance i≤β☆ s not fixed, resulting in cavity noise₽φ♦. When the current passes through♥ ♥€ the inductor, the magnetic field genφ→←erated by the inductor coil wil✔→↕l cause the coil positi¶φ​≈on to move. When the curreβΩ nt disappears, the position will★>∏♣ be restored. If the inductance  ∏®$coil is not fixed and th←§★ere is a switch excitation c✔Ωurrent frequency between βλ 20Hz-200Hz, the inductance coil may vib¶≠₽≤rate and compress the  ↔surrounding air due to cyclic position<→< changes, which can easily form audible®'± cavity noise, namely inductance whist↔¥×ling.

Sometimes the switching frequ€¥£•ency is not between 20HZ-♣★20KHZ, and there may also be induc•← ©tance whistling. The r €₩↑eason is that the load is unstable, ☆₩↓£and a more common one is t"π>he power inductor howlin™πg in DC-DC circuits.

The reason for the power $↕↓™inductance of DC-DC circ♠≠ uit whistling is that the load curreγ¶nt is too large. At thφ¶÷±is time, the power inductance has been ✘♦±saturated, the inductance value becoβ☆∞'mes smaller, and the char↑±ge and discharge cur♥α→$rent speed of the inductance ™≤rapidly increases. The i↓☆≠nternal current limiting¥÷€  protection circuit will imm ‌$✔ediately adjust the ¶≥'©duty cycle of the DAC internal swi'Ωtch, or immediately stop the®≈£ε switch operation until the d≈‍etection current is within the stand€®♠ard range, and then resume the norm ∏al working switch, w₽‌±÷hile the stop and resume♦§ ☆ Switching frequency is exactly betw£≤≈een 20Hz and 200Hz, So the✔↓ &re is an inductance howling.

Another reason for t∑←he howling of the in‍λ≤ductor is the occurrence of ma©<gnetostriction in the magnetic>§π÷ core, and the freque¥♦ncy range of the cur∏××÷rent ripple that drives thεδ→​e magnetostriction of the i→☆₽Ωnductor core is precisely ar‌¥‍ound 20HZ-20KHZ.

How to solve the problem of inductanceπβφε whistling?
How can we solve the cause of ©≤↑×the above inductance w€•∏‌histling? Here are four so‍$§lutions to teach you:
Method 1: After immersing the inducto σr in the adhesive, use a vacuum box toα↕©≤ empty the bubbles inside the adhes→©♦φive to fix the coil a‍₹♥nd solve the problem of induc<™tance howling caused by >☆©↔the unstable inductance (PS ♠β: it is better to use epoxy resinε₩σ♣ hard sealing material for "↓∑immersing the adhesive)
Method 2: Reducing the lo$α>ad current can solve the problem of±γ  inductance whistling. 3
Method 3: Starting from the switc↓δ&φh duty cycle, stabilizing t₩§he DC-DC switch duty cycl₹πe can fundamentally solve the problem<®↕ of inductance whistling
Method 4: Replace the howling δ₽ε inductor with a higher saturated power✘↕ inductor or a slightly higher≠<'± power DC-DC chip