원문 게시자: cns ,
The headphone jack on an iPhone 4S does not supply power. It has 3 contacts. It supplies left/right audio and a control signal and has a ground. It does not supply power in the "power supply" sense of the term. One cannot power other equipment from the headphone jack. It does supply a certain amount of power - audio power - measured in milliwatts, I believe. But that cannot be used to power another mp3 player (for instance) with operating power. But the audio signal can and will drive an amplifier that gets it's own operating power from it's own internal power supply.