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Analysis Of The Cause Of Abnormal Noise Caused By Switching Power Supply Transformer

The whistling sound of the transformer is mainly due to the low frequency oscillation in the excitation component of the transformer, so that the magnetic molecules of the magnetic core move under this low frequency magnetic field, causing mechanical vibration, thereby causing vibration of the surrounding air. Since the audible frequency of the human ear is about 20 Hz to 20 kHz, if the vibration of this air is within this range, it is finally transmitted to the human ear and is heard.

There are four main reasons for the whistling of the switching power supply transformer: the process problem of the transformer, the loop problem of the transformer, the core problem of the transformer and the load problem of the switching power supply.

Switching power supply

1, the core problem of the transformer

When the transformer core is saturated, the current in the coil increases, the transformer generates heat and generates self-excited oscillation, and the oscillation of the coil causes vibration of the surrounding air to make a sound.

2, the switching power supply load problem

2.1, the transformer works in a serious overload state, there is always the possibility of burning - this is the origin of many "screams" before the power supply burned.

2.2. Switching power supply Under the condition of no load or light load, oscillation will occur at some working points, which is manifested by the whistling of the transformer and the instability of the output.

This phenomenon occurs because the instantaneous turn-on time of the switch is too large due to the no-load/light load, resulting in too much output energy, and the voltage overshoot is also large. It takes a long time to recover to the normal voltage, so the switch needs to stop working. For a period of time, the switch operates in an intermittent mode of operation, causing the transformer to vibrate at a lower frequency (a regular intermittent full cut-off period or a frequency at which the duty cycle changes drastically).

3, the process of the transformer

3.1, the line package is not tightly wounded may also cause noise;

3.2, the core combination has an air gap, causing air vibration and sound when high frequency (the transformer will not sound if it is fully immersed in vacuum);

3.3, the dipping paint is not in place, causing the magnetic core to be weak and causing mechanical vibration to make a sound;

3.4. The length of the air gap is not suitable, which causes the working state of the transformer to be unstable and makes a sound.

4, the loop problem of the transformer

The loop problem of the transformer means that the loop of the transformer oscillates and causes the transformer to whistle.

4.1. Quality problems of components in the loop, such as insufficient capacity of the input filter capacitor, poor quality of the output rectification fast recovery diode, poor quality of the power MOS tube, poor quality of the high voltage capacitor or diode of the RCD recoil absorption loop, etc. These problems can cause shocks and cause noises;

4.2, the circuit board is improperly wired, causing interference to cause oscillation, resulting in noise;

4.3 The feedback loop parameters are set incorrectly, causing the loop to be unstable and causing oscillations to make a sound.