Quote:
Originally Posted by Al Skierkiewicz
Not exactly, what you are hearing are two different things. The high frequency you hear in a flash charging is the actual oscillator used in the DC-DC converter. It changes frequency because the feedback that causes oscillation is dependent on load current. As the capacitor charges the load current becomes less so the frequency rises.
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As a cool side note:
Ceramic capacitors have a slight piezoelectric effect. They make very good (obnoxious) speakers in these sorts of circuits. They also make electrical noise when you tap on them.