If your USB device ever suffers from noise caused by an earth loop or if you want to protect your PC against external voltages then you need a USB isolator. The circuit described in Elektor's October 2012 edition offers an optimal electrical isolation of both the data lines as well as the supply lines between the PC and the USB device.
• Electrically isolated data and power supply lines
• Configurable data rate of 1.5 Mbit/s or 12 Mbit/s
• Power for the device side can be taken from an extra USB host connection or an external AC power adapter (5 V/min. 0.5 A)
• Transformer isolation = 1500 VAC for 1 min
• ADuM3160 isolation = 565 Vpeak for 50 years
• Maximum output current Iout = 500 mA @ 5 V