22.11.2013

Usb power cable nz

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?
In fact, the device is powered from two USB ports, since one port is incapable of supplying sufficient current. 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. The 5V Breadboard Power Supply allows you to easily power your breadboard or any other circuit with a smooth regulated 5V supply.
Protection diodes to protect from incorrect polarity and when both the USB and wall wart are connected at the same time. Simply enter your details below and we will send you an e-mail when “5V Breadboard USB Power Supply - kit” is back in stock! We will not send you any other e-mails or add you to our newsletter, you will only be e-mailed about this product!
Another useful bit to make yourself might be a cable with an inline fuse and a cigarette lighter plug so you can tap into a vehicle supply (note that this may be up to 14.4 V with a running engine). The Vbus supply from USB socket CON1 turns on transistor Q1 which then turns on power Mosfet Q2. The compact size also makes it a perfect candidate for building in to any finished product that requires a regulated 5V power supply.


Although a matching charger is usually supplied in the package, there are also devices that can only be charged via a USB port. At an output current of 1 A and an input voltage of just 7 V, the 7805 already dissipates 2 watts. 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. 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. A newly-acquired Maxtor OneTouch4 Mini drive also failed to power up correctly on my home computer, despite working perfectly on several work computers. This then feeds a 6V DC regulated supply from an external plug pack to regulator REG1 which in turn supplies 5V to USB socket CON2. That is not surprising in the case of USB MP3 players, which have to ‘dock’ in the PC anyway for some time for the purpose of file transferring. The 7805 comes in different flavours most devices can supply 1 A, but there are also more advanced variants that achieve up to 1.5 A. As with most such drives, it is powered directly from the USB port, so it doesn’t require an external plug pack supply. One connector is wired for both power and data while the other connector has just the power supply connections.


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 identify the device and certainly didn’t recognize the drive. Still, the same ‘feature’ can be a serious disadvantage, for example, on ‘computer-free’ holidays. Also assuming that the ambient temperature is 20 °C, the 7805’s internal (chip) temperature will be around 120 °C.
In use, the two connectors are plugged into adjacent USB ports, so that power for the drive is simultaneously sourced from both ports.
Sometimes it makes you wonder how simple the solutions to such problems actually turn out to be.
The input voltage may be a direct voltage of anything between 7 and 24 volts, so for use at home or abroad a simple wall cube with DC output is sufficient. In most cases, 150 °C is the specified maximum, so ample cooling must be provided especially in a car and with relatively high input voltages.



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