Boot time to paste up to listen to a little, shut down without being able to hear. Before not pay attention, yesterday only to find such a thing, this normal?
If the sound is not particularly ringing, it is normal.
The laptop's power adapter is a switching power supply. Switching power supply of high-frequency transformers in the work, due to the role of high frequency, will produce mechanical waves, because the normal work of the normal switching frequency is much higher than the human ear hearing range, it is difficult to hear, and when the load is very light, The frequency of the switch will fall within the hearing range of the human ear.
Power adapter for the host power supply and battery charging, 220V AC voltage can be reduced to the voltage suitable for notebook computers, in the process of converting the current due to electromagnetic phenomena emitted by the electromagnetic sound, and will send a certain amount of heat, Can not worry. If the electromagnetic sound of the power adapter suddenly becomes larger and the abnormal heat condition occurs, the power adapter should be unplugged immediately and the machine should be checked with the power adapter after turning off the machine.
Notebook power adapter generally use the switch circuit, the output 12V DC power supply.
1, as the notebook DC / DC converter circuit power supply, in the switch circuit, the most prone to "creak" sound is the switch transformer coil (ringing), or high-voltage filter capacitor (fire);
2, it may be the power adapter has been thrown, may make high-voltage filter capacitor loose or desoldering, which issued a "creak" sound;
3, it is possible to switch the coil of the transformer shock, issued a sound.
