Bitzie USB DAC/USB Headphone Amp: a USB bus-powered USB DAC
"USB DAC for Samsung Galaxy S3 Android Jellybean...
7.5hrs continuous playing!"
Like any other USB peripheral, a USB DAC can be:
. a bus-powered device:
The USB DAC draws power from a USB host (PC or USB-host enabled Android device).
The maximum power a USB DAC can draw is 500 mA according to the USB specification.
. a self-powered device:
The USB DAC draws power from its own battery.
More and more USB DAC manufacturers target the big smartphone (i.e. portable device with small battery) market by providing self-powered USB DAC like FiiO with the E18 or Chord with the Hugo:
Hugo has a built-in battery-charging circuit, with a full charge reached in approximately two hours. Hugo takes no power over its USB input (as this is severely limited with many partnering products) and only takes signal data, therefore, it is fully compatible with all iPhone, iPad and Android devices."