The reason for the whistling of the switching power supply transformer
1. Technical problems of transformers
① The dipping paint is not dried properly, resulting in the weak magnetic core causing mechanical vibration and making noise;
②The length of the air gap is not suitable, which leads to the unstable working state of the transformer and the sound;
③If the wire package is not tightly wound, it may also cause noise;
④ There is an air gap in the magnetic core combination, which will cause the air to vibrate and make a sound at high frequencies (if the transformer is fully immersed in a vacuum, it will generally not make a sound).
2. The loop problem of the transformer
The loop problem of the transformer means that the loop of the transformer oscillates, which causes the transformer to whistle.
① Improper wiring of the circuit board, resulting in interference and oscillation, resulting in noise;
② Improper setting of feedback loop parameters will cause the loop to become unstable, resulting in oscillation and sound;
③Quality problems of components in the loop, such as insufficient input filter capacitor capacity, poor quality of output rectifier fast recovery diode, poor quality of power MOS tube, poor quality of high-voltage capacitor or diode of RCD recoil absorption circuit, etc. Problems may cause vibration and cause noise.
3. Transformer core problem
When the iron core of the transformer is saturated, the current in the coil increases, the transformer heats up and generates self-excited oscillation, and the oscillation of the coil causes the vibration of the surrounding air to make a sound.
4. Load problem of switching power supply
①In the case of no load or light load, the switching power supply will oscillate at some operating points, which is manifested as the howling of the transformer and the instability of the output. This phenomenon occurs because the instantaneous turn-on time of the switch is too large at no load/light load, 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, this switch operates in an intermittent mode of operation, causing the transformer to vibrate at lower frequencies (regular intermittent full-off periods or frequencies with drastic changes in duty cycle).
②The transformer works in a serious overload state, and there is a possibility of burning it at all times. This is the origin of the "screaming" before many power supplies burn out.
