Analysis on the cause of abnormal sound of switching power transformer

The noise of the transformer is mainly due to the transformer's excitation component contains low-frequency oscillation, which makes the magnetic molecules of the magnetic core move under this low-frequency magnetic field and generate mechanical vibration, thus causing the vibration of the surrounding air. Since the audible frequency of the human ear is about 20Hz to 20kHz, if the vibration of the air is within this range, it will eventually be heard by the human ear.
There are four main reasons for the noise of the switching power transformer: the transformer's process, the transformer's loop, the transformer's core and the load of the Switching Power Supply.

1. The core of the transformer
When the transformer core is saturated, the current in the coil increases, and the transformer heats up and generates self-excited vibration.
2. Load of switching Power Supply
2.1 the transformer is working in a seriously overloaded state and may be burnt down at any time -- this is the reason why many power sources "scream" before being burnt down.
2.2 under the condition of no load or light load, the switching power supply will oscillate at some working points, which is manifested by the noise of the transformer and the instability of the output.
Happen this kind of phenomenon is due to the light/light load, the switch instantaneous opening is too big, too much time to output energy and voltage overshoot is big, need a long time to return to normal voltage, so switch to stop work for a period of time, this switch is working in the intermittent work mode, the transformer in low frequency (regular intermittent full cutoff period or the frequency of the dramatic change duty ratio) of vibration.
3. Process of transformer
3.1 if the package is not tightly wound, it may also cause noise;
3.2 there is an air gap in the magnetic core assembly, which causes air vibration and makes a sound at high frequency (if the transformer is completely immersed in vacuum, it generally does not make sound);
3.3. The paint immersion drying is not in place, resulting in the magnetic core is not firm, causing mechanical vibration and sound;
3.4 the length of air gap is not suitable, resulting in the transformer's working state is unstable and makes a noise.
4. Circuit problem of transformer
The problem of the transformer's loop is that the transformer's loop oscillates and causes the transformer to scream.
4.1 quality problems of components in the loop, such as insufficient capacity of the input filter capacitor, poor quality of the output rectifier quick recovery diode, poor quality of the power MOS tube, poor quality of the high voltage capacity of the RCD recost-absorption loop or poor quality of the diode, these problems may lead to vibration and cause noise;
4.2 improper wiring of the circuit board, resulting in interference and vibration, resulting in a sound;
4.3 improper setting of feedback loop parameters leads to unstable loop, resulting in vibration and noise

Best Regards,

Una Yang