Method of sensing connection of usb device in power save mode and image forming apparatus for performing the same

A method of sensing connection of a universal serial bus (USB) device when an image forming apparatus is in a power save mode, the method comprising:

• turning off a USB host controller of the image forming apparatus when the image forming apparatus enters the power save mode;
• outputting a wake-up signal to a main controller of the image forming apparatus when a USB device is connected to a USB port of the image forming apparatus and a voltage change occurs on a voltage bus (VBUS) line that supplies power to the USB port;
• receiving the wake-up signal by the main controller;
• and
• turning on the USB host controller by the main controller.

An image forming apparatus comprising:

• a main controller;
• an external device interface;
• a power supply to supply power to the external device interface through a power supply line;
• a voltage change detector to output a wake-up signal to the main controller if a voltage change occurs on the power supply line;
• wherein the main controller turns off one or more components of the image forming apparatus when the image forming apparatus enters a power save mode, and the main controller turns on one or more components of the image forming apparatus when the wake-up signal is received from the voltage change detection unit.