There are more and more users of portable HDD, because of its large capacity and high transfer speed. As we know, the interface of HDD is USB, we need no drive, can directly connect with PC under the operating system Windows Me/2000/XP,and the speed is much faster than softdrive. But usually we find such a condition, PC system show that it find unknow USB device, but it cannot discern portable HDD. What reasons causes such a condition? Reasons : The following are the reasons: 1. insufficient power supply of USB system distributed maximum 500 mA to each usb. In general condition, usb flash disk just needs 100mA, so when we use usb flash disk, usually will not accur such a condition. And most portable HDD are 2.5 inch HDD, and its working electric current is between 500mA~1000mA, if the power is supplied by USB, and there are no other USB in the system, it can work. But if the working voltage is not instable, it will accur such a condition. If the interface is USB2.0, and use battery to provide power, this condition will be more serious. 2. use external USB expansion card If we use USB2.0 HDD and other high capacity storage device, and the laptop doesn’t support USB 2.0, generally speaking, we have to use PCMCIA transfer to USB2.0 expansion card to support the connnect, and nearly all the expansion cards use D720100AGM USB control chipset (NEC company), it provides at least 2-5 USB2.0 interface, this is enough for most users. The power supplied by PCMICA interface is lower than the power supplied by board USB, so it causes insufficient power supply Solutions: According to the experience, such a condition just accured to large capacity USB device, and the solution is very easy, use power compensation cable, or use DC power, if this accessory is provided.
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