A method of powering an audio
output device of a computer
system, by determining whether a passive or active audio
output device is connected to an audio output jack of the computer
system and, based on this determination, providing an appropriate
power level to the audio output jack. For example, if the determination is made that a passive audio
output device is connected to the audio output jack, then a 3-
watt power
signal is applied to the audio output jack, but if the determination is made that an active audio output device is connected to the audio output jack, then a ΒΌ-
watt power
signal is applied to the audio output jack. The type of audio output device present may be determined by sensing an impedance at the audio output jack. This sensing may be performed by comparing a load
voltage associated with the impedance to a reference
voltage. The output of a switch device (
multiplexer) having a first input from an AC97 audio codec and
headphone amplifier and a second input from a passive speaker
amplifier is selectively controlled by the sensing circuit.