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From a quick price-check on ebay,

  • Passive (bus-powered) USB Hubs - ~ $2-$5
  • Powered (externally) USB Hubs - ~ $15-$20

My use-case is to expand the no. of USB ports on a ARM-based SBC, and to embed the hub in the same enclosure, so I was wondering, if it is possible to just add a regulated (7805 based) wall-wart power adapter, to supply extra current to the devices.

  • Is there some per-port and up-stream protection circuit required ?
  • Does it make a difference if the host-port is USB1.0 / USB1.1 / USB2.0 (from the point of view of converting the hub to a powered one) ?
  • Are there some gotcha's with this approach, which I might be missing ?

BTW, if someone is aware of an existing "embeddable" USB hub circuit schematic, which isn't more expensive (BOM-wise) than the ebay consumer devices, would appreciate a pointer.

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    \$\begingroup\$ If you do this, isolate the regulator from USB +5v. Do NOT connect the two together. The USB hub inside the computer may draw power from your 7805 and will cause a problem. \$\endgroup\$
    – Bryan Boettcher
    Sep 13, 2012 at 21:35
  • \$\begingroup\$ Good point @insta. \$\endgroup\$
    – bdutta74
    Sep 14, 2012 at 6:44
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    \$\begingroup\$ TI has several very reasonably priced USB hub controllers (e.g, TUSB2046B, TUSB2077A), with implementation schematics in the datasheet. \$\endgroup\$
    – user39382
    May 23, 2014 at 6:19

2 Answers 2

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The (externally) powered USB hub I have just connects the power supply to the appropriate pins of the USB connectors. Power from the PC is connected trough a diode, so the hub can be powered by the PC or the power supply.

USB specification says that devices should negotiate for the power with the hub or PC, but in practice, just connecting the 5V to the required pins works just as well, especially if the power supply is powerful enough for all devices. Some USB devices (battery chargers, lamps, fans etc) do not negotiate for the power, just connect the power pins to whatever is needed.

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  • \$\begingroup\$ Thanks @Pentium100. That sounds like a rather simple and practical approach. I am looking at pitfalls of that approach as well, to make an informed decision. If specs have provision for negotiating power source, I assume there to be a good reason for same. In the end, I might as well, land up taking the simple approach. \$\endgroup\$
    – bdutta74
    Feb 2, 2012 at 4:38
  • \$\begingroup\$ Found some useful info on the Wikipedia page on USB hub in the Power section. \$\endgroup\$
    – bdutta74
    Feb 2, 2012 at 4:41
  • \$\begingroup\$ @icarus74 check out the USB 2.0 power specification at: usb.org/developers/docs to get more info. \$\endgroup\$
    – colemik
    May 27, 2012 at 22:13
  • \$\begingroup\$ If anybody else is doing this a simple way to do this is to buy a 99 cent USB extension cable off of eBay and just snip the 5V line and solder the + and - of the wall wart to the adapter accordingly and plug the hub into one end and the other into the computer. The real reason I posted is to point out you may want to add some capacitors to clean up the power supply; electronics like that are touchy. electronics.stackexchange.com/questions/8405/… \$\endgroup\$
    – Anonymous Penguin
    Mar 11, 2013 at 19:22
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I just converted an el-cheapo USB hub to Powered USB Hub, using the Diode method someone posted earlier. I also added a LED so I am sure Hub is working fine. Just tested it using 5v Nokia Charger as power supply, and by connecting USB Mouse+ android + chill pad (thermal master) + a USB Pen Drive, all together never worked earlier on this HUB, they worked like a charm once I connected the tiny nokia charger which gives 5V regulated output.

I might do more experiments later by attaching a LM 7805 based supply to it to see if it can run a laserJet too.

snaps the cheap HUB inside of hub components used added parts Up and running, the D.I.Y. USB, External powered HUB

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