What causes the transformer of the power supply to make a sharp noise?

Principle of transformer whistling

The transformer whistle is mainly due to the transformer's excitation component contains low-frequency oscillation, so that the magnetic molecules of the magnetic core move under this low-frequency magnetic field, resulting in mechanical vibration, which causes the vibration of the surrounding air. Since the audible frequency of the human ear is about 20Hz to 20kHz, if the vibration of this air is in this range, it will eventually reach the human ear and be heard.

The reason why the transformer whistles

There are four main reasons for the noise of the switching power 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, which are analyzed as follows:

1, transformer process problems

01 Dip paint drying is not in place, resulting in weak magnetic core causing mechanical vibration and sound;

02 The length of the air gap is not suitable, resulting in unstable working state of the transformer and sound;

03 wire wrap not tightly wound may also cause noise;

04 The core combination has an air gap, which causes air vibration and sound at high frequency (if the transformer is fully immersed in vacuum, it generally does not sound).

2, transformer loop problem Transformer loop problem

That is, the transformer loop oscillates and causes the transformer to roar.

01 Circuit board wiring is improper, which causes interference to cause oscillation, resulting in sound;

02 Improper setting of feedback loop parameters leads to instability of the loop resulting in oscillation and sound;

The quality problems of components in the 03 loop, such as insufficient input filter capacitance, poor output rectifier fast recovery diode quality, poor power MOS tube quality, high voltage capacitor or diode quality of the RCD backlash absorption circuit, etc., these problems may lead to vibration and cause sound.

3, the transformer core problem

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

4, switching power supply load problem

01 In the case of no-load or light load, the switching power supply will oscillate at some operating points, which is manifested as the transformer screaming and the output instability. This phenomenon occurs because when no load/light load, the instantaneous opening time of the switch is too large, resulting in too much output energy, and then the voltage overshoot is also large, and it takes a long time to restore to the normal voltage, so the switch needs to stop working for a period of time, so that the switch works in intermittent working mode. Vibrate the transformer at lower frequencies (regular intermittent full cutoff periods or frequencies with dramatic changes in duty cycle).

02 transformer working in a serious overload state, there is the possibility of burning at all times - this is the origin of many power supplies before burning "screaming".For more information, please contact us at sales@xfullstar.com