USB Power Injector For External Hard Drives


Posted on Feb 7, 2014

A portable USB hard drive is a great way to back up data but what if your USB ports are unable to supply enough juice  to power the drive A modified version of the Silicon Chip Usb Power Injector is the answer. For some time now, the author has used a portable USB hard drive to back up data at work. As with most such drives, it is powered direc


USB Power Injector For External Hard Drives
Click here to download the full size of the above Circuit.

tly from the USB port, so it doesn`t require an external plug pack supply. In fact, the device is powered from two USB ports, since one port is incapable of supplying sufficient current. That`s done using a special USB cable that`s supplied with the drive. It has two connectors fitted to one end, forming what is basically a Y  configuration (see photo). One connector is wired for both power and data while the other connector has just the power supply connections. In use, the two connectors are plugged into adjacent USB ports, so that power for the drive is simultaneously sourced from both ports. An external USB hard drive is usually powered by plugging two connectors at one end of a special USB cable into adjacent USB ports on the computer. This allows power to be sourced from both ports. According to the USB specification, USB ports are rated to supply up to 500mA at 5V DC, so two connected in parallel should be quite capable of powering a portable USB hard drive at least in theory. Unfortunately, in my case, it didn`t quite work out that way. Although the USB drive worked fine with several work computers, it was a no-go  on my home machine. Instead, when it was plugged into the front-panel USB ports, the drive repeatedly emitted a distinctive chirping sound as it unsuccessfully tried to spin up. During this process, Windows XP did recognise that a device had been plugged in but that`s as far as it went it couldn`t...




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