as follow
The standard voltage of the USB interface is 5V and the standard current is 500mA. In actual use, according to the influence of various factors such as the computer motherboard and power supply, there may be errors, but the maximum cannot exceed \/-0.2V, that is, 4.8-5.2V.
USB devices have the following advantages:
1. Unified standards. We are common IDE interface hard disk, serial port mouse keyboard, parallel port printer scanner, but with USB, these application peripherals can all use the same standard and personal computer connection, then there is a USB hard disk, USB mouse, USB printer and so on.
2. Multiple devices can be connected. USB often has multiple interfaces on personal computers, can be connected to several devices at the same time, if connected to a USB with four ports, you can be connected; Four USB devices, and so on, can be connected to all the devices in your home at the same time on a personal computer without any problems (note: up to 127 devices can be connected).