| 摘要 |
A USB(Universal Serial Bus) device is provided to reduce the volume of a USB device adaptor as well as a manufacturing cost by receiving electric power from a USB host, or supplying the electric power to the USB device adaptor. A PSU(Power Supply Unit)(310) generates the electric power. An internal circuit(320) performs a function and transceives data with the USB host or device adaptor through the USB cable. The first switch(SW1) switches between one USB cable terminal connected to one terminal and the PSU connected to another terminal by the first control signal. The second switch(SW2) switches between one USB cable terminal connected to one terminal and the internal circuit connected to another terminal by the second control signal. A controller generates the first and second signals. If the USB device is directly connected to the USB host through the USB cable, the first switch is opened and the second switch is closed when the USB device receives the electric power from the USB host through the USB cable.
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