Eli5 Why chargers make high pitched noise when battery is full?
In: 25
Your charger is an ac to dc switch mode power supply. High voltage ac is converted to dc and the conversion circuit uses a high frequency signal with a small transformer and transistors. These are usually switched at just barely a high enough frequency that it should almost be out of hearing range.
That high pitch sound is not 60 hz as others have suggested. 60 hz is a hum, not a squeal.
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