If your USB device ever suffers from noise caused by a ground loop or if you want to protect your PC against external voltages, then you need a USB isolator. Elektor’s USB Isolator, published in our 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.
The project itself is a spin-off from an earlier design for a portable oscilloscope for Android. During the development of that project, we encountered problems with ground loop noise when a charger or PC was connected. But where would the best point to introduce electrical isolation be, in the digital USB connection or in the analogue section? After some serious analysing, we came to the conclusion that it was better to isolate the USB bus rather than the analogue part. A popular chip from Analog Devices, the ADuM3160, was chosen to provide the isolation of the data lines. It supports both Low and Full speed USB connections. A flyback converter based on an LT3575 was used to isolate the power supply.
Elektor’s USB Isolator at a glance:
• 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
Since several components are very tricky to solder due to their size, and some are also not easily obtainable, Elektor has made a fully populated board available, including the case. All you need to do is to make a few holes for the connectors and slide switches in the two side panels of the case.
The populated and tested board is available from the Elektor Webshop for just £62.30 / €69.95. Elektor Magazine Members take advantage of no less than 10% discount.