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Power adapter load problem analysis
time2006/05/22
- The power adapter will oscillate at some working points under no-load or light-load conditions, which is manifested by the whistling of the power adapter transformer and the instability of the output.
Power adapter transformer process problem
1. The dipping paint is not in place, causing the magnetic core to be weak and causing mechanical vibration to make a sound;
2. The length of the air gap is not suitable, causing the working state of the power adapter transformer to be unstable and making a sound;
3. The winding of the wire package may also cause a sound;
4. The magnetic core combination has an air gap, causing air vibration and sound when high frequency (the power adapter transformer is fully immersed in vacuum, and the epoxy resin in the middle column, the epoxy resin between the skeleton and the core) - refer to the following frame The location that comes out will generally not sound).
Power adapter transformer loop problem
The loop problem of the power adapter transformer means that the loop of the transformer oscillates and causes the transformer to whistle.
1.Improper wiring of the board, causing interference to cause oscillation, resulting in noise;
2. Improper setting of the feedback loop parameters causes the loop to be unstable to cause oscillation and sound;
3. The quality of the components in the loop, such as the insufficient capacity of the input filter capacitor, the quality of the output rectification fast recovery diode is not good, the quality of the power MOS tube is not good, the high voltage capacitance of the RCD recoil absorption loop or the quality of the diode is not good, etc. It can cause shocks and cause noise.
Transformer core problem
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.
Power adapter load problem
1. The power adapter will oscillate at some working points under no-load or light-load conditions, which is manifested by the whistling of the power adapter 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 power adapter transformer to vibrate at a lower frequency (a regular intermittent full cut-off period or a frequency at which the duty cycle changes drastically).
2. The power adapter transformer works in a severe overload condition and there is always the possibility of burning - this is the origin of many "screams" before the power supply burns out.