USB hub follies

Dec 29, 2017 3 Replies
P

We're getting ready to ship a bunch of systems to our fire prevention customer, and to our horror found that the FTDI 230 USBserial chip was getting super hot and shutting down.



After a bit of digging around, it turned out to be a Sabrent HB-U14P USB which was dragging USB- *below ground* by about 400 mV. Works fine with a normal 0-3V swing on the USB.



I bought the thing off Amazon, so it should be legit, but whoever heard of a USB hub with a negative supply internally?



A pity--I've had good luck with Sabrent gear up till now.



Anybody got a fave decent-quality USB hub?



Cheers



Phil Hobbs


Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
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J

The Sabrent HB-U14P is a 13 port USB 2.0 hub. If you really need 13 ports, it's going to be difficult to find a replacement. AliExpress has some possibilities (which I haven't tried):

I've had difficulties with a similar 7 port USB 2.0 hub. The problem turned out to be the junk power supply. Fully loaded with 7 devices, each port consuming about 300 ma, the 5V 1A power supply would not supply the needed 2.1A. When I replaced it with a 5V 2A power supply, the PS protested by going into oscillation. That might be the source of the negative voltage. When I ran it from a 5v 20A bench power supply, it worked, but the hub became rather warm. Note that 300ma per port is well below the 500ma per port allowed by the hub specifications. I can imagine that 13 ports drawing a total of 6.5A at maximum load, would be worse. Anyway, look for power supply overload, fold back, and oscillations.

Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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P

I just tossed it. ;)

We don't actually need that many ports anyway. I'm not sure how an oscillating PSU is going to generate actual negative rail voltages, especially since it has only two wires, but it's an interesting idea.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
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L

a switch or something like that in the supply ground for the output ports?

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