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USB POW
- Simple USB power injector -



Completed USB POW icon

     USB POW is a simple power injector I designed for use with USB devices. The USB POW has USB data input and output ports, as well as a DC input jack and a spare USB power output port. It is designed to allow high-power USB devices to work reliably with long USB cables and/or under-powered USB hubs / host controllers.


The Idea  |  Specs  |  Materials  |  Schematics  |  PCB Layout  |  Considerations  |  All Photos  |  License



The Idea:

     The USB standard restricts the current consumption of all USB devices to either 100mA or 500mA depending on the specifics of the USB hub and/or host controller (i.e. computer) that is supplying the power. Ideally, no USB device should ever pull more than 500mA of current from a USB port. In reality this is not always the case.

     There are two main issues that can cause a USB device to attempt to exceed the 100mA or 500mA limit. The first is high "inrush" current during the startup of some USB devices. For example, a USB hard drive trying to spin up can temporarily attempt to pull much more than 500mA from its USB port. The second issue is the connection of high-power USB devices through long USB cables or active USB "repeaters" (really really long USB cables.) In both cases, the large voltage drop that can occur over the length of such USB cables will cause some USB devices to be under-powered and fail to work reliably... or at all.

     Lastly, some USB host controllers are notorious for being "weak" and unable to provide the full power required by the USB standard. Weak host controllers are found in some laptops and peripherals with integrated USB hubs (such as computer monitors, printers, etc..) USB POW is also ideal for allowing high-powered USB devices to work reliably with under-powered host controllers and hubs.


Specifications:

  • Input Power: 5 Volt, 1 Amp maximum
  • Input Connections:
    • USB type B female (Data and power)
    • 2.1mm x 5.5mm female DC power jack
  • Output Connections:
    • USB type A female (Data and Power)
    • USB type A female (Power only)
  • Indicators: LEDs for bus power and external power input
  • Dimensions: 46mm x 40mm x 14mm (L x W x H)

Materials List:

USB POW parts list

     Notes:

  • The power supply, PS1 must provide a well-regulated 5VDC output.
  • Diode D1 can be almost any type, but the use of a Schottky diode is highly recommended.
  • The LEDs can be almost any type, but the value of resistors R1 and R2 may need to be changed
  • Schematic and PCB revision 1.2 assumes the DC input jack polarity is Tip = Negative, Ring = Positive
  • Schematic and PCB revision 1.3 assumes the DC input jack polarity is Tip = Positive, Ring = Negative

Schematics:

     Below are the schematics for USB POW. The latest schematic is revision 1.3. Older schematics are also shown, but only for historical information. They are not guaranteed to work correctly.

     Use the following links to: [ Download Schematic v1.3 ]    [ Download Schematic v1.2 ] as Eagle schematic files.

USB POW 1.3 Schematic      USB POW 1.2 Schematic
USB POW Schematics (newest version is on the left)


PCB Layout:

     The printed circuit board for USB POW is a standard 2-layer board. Board revision 1.3 allows USB POW to be used with DC power supplies whose polarity is tip = positive, ring = negative. Board revision relies on the less common polarity tip = negative, ring = positive for proper operation. Use the following links to:
[ Download PCB v1.3 ]    [ Download PCB v1.2 ] as Eagle board files.

USB POW 1.3 PCB      USB POW 1.3 PCB Silkscreen      USB POW 1.3 PCB Top Layer      USB POW 1.3 PCB Bottom Later     
USB POW PCB layout -- Revision 1.3


USB POW 1.2 PCB      USB POW 1.2 PCB Silkscreen      USB POW 1.2 PCB Top Layer      USB POW 1.2 PCB Bottom Later     
USB POW PCB layout -- Revision 1.2



USB POW - Rev. 1.2 Photos

Photo Gallery USB POW
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Photo Gallery USB POW
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Photo Gallery USB POW
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Photo Gallery USB POW
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Photo Gallery USB POW
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Photo Gallery USB POW
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Photo Gallery USB POW
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Photo Gallery USB POW
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Photo Gallery USB POW
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Licensing Information:

Creative Commons License The USB POW schematics and printed circuit board layouts are licensed by Nick Viera under the Creative Commons Attribution-Share Alike 3.0 United States License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/us/ or send a letter to Creative Commons, 171 Second Street, Suite 300, San Francisco, California, 94105, USA.