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The cause of inductor whining is when the frequency of the switch current output from the voltage regulator power supply circuit is close to or falls within the audio range, or when the frequency of periodic square wave groups is close to or falls within the audio range. The periodic current passing through the inductor coil generates an alternating magnetic field, causing the coil to vibrate and produce sound. If the periodic pulse group with a frequency close to or within the audio range is discarded, inductor whining may occur. Similarly, if the frequency of the down-converted switch current is close to or falls within the audio range, it can also cause inductor whining.
When the inductor is operating in DC mode, there is a constant switch current of around 1 MHz at both ends of the inductor coil. The variation in this current causes the coil to vibrate and produce a sound of around 1 MHz, which is not audible to humans.
If the whining sound is audible, it can be determined that there is a switch current of around 20 Hz to 20 kHz at both ends of the inductor.
Inductor whining in DC-DC circuits:
A. Excessive load current: Solution: Reduce the load current or replace the DC-DC converter with a slightly higher power rating.
B. Overvoltage protection: Solution: Reduce the load current or replace the DC-DC converter with a slightly higher power rating. To fundamentally solve the instability of the duty cycle, the small signal of the control loop is generally disturbed by noise. The duty cycle of the DC/DC converter needs to be adjusted to be stable. It may also be caused by the expansion and contraction of the magnetic core, in which case the inductor can be potted.
