RPi Powered USB Hubs

A number of low-cost powered USB hubs are known to have caused problems. Members of the Raspberry Pi forums have reported low power or no power at all in some cases. The following is a list of specific Powered USB Hubs which appear to be fault-free. Please note that these do not take into account powering the Raspberry Pi from the hub, in addition to its peripherals. If you use a powered hub and the Raspberry Pi PSU together consider powering them from the same power bar with switch, so you can turn them on simultaneously., especially if the HUB tries to feed the Raspberry Pi through their interconnect cable, due to the 100 mA limiting fuse in the Raspberry Pi, the Raspberry Pi will be partially powered which may cause problems (unwanted writes to the SD card).

Raspberry Pi Specific Hubs
Recently, two new hubs have been designed and manufactured specifically for the Raspberry Pi. Guaranteed to provide no back power to the unit. These are
 * 1) Raspberry Pi 7 Port USB Hub from The Pi Hut
 * 2) Pimoroni PiHub 4 port USB hub and 3 A power supply. One of the 4 USB ports supplies the Raspberry Pi with dedicated full 1 A power over a standard USB A to micro B cable. (Order cable separately.) See Raspberry Pi foundation September 9, 2013 news: PiHub - a robust powered hub, made especially for your Raspberry Pi.

Working USB Hubs
'*' Power Ratings may not be completely accurate, use as rough guideline rather than fact.


 * Acme
 * USB 2.0 hub 4 port (ACME) Based on NEC μPD720114 USB2.0 Hub Controller USB ID 0409:005a  NOTE! It is bus-powered hub, but it is very cheap and small and works after a small modding: on USB-hub board you have 4 holes: V, D+, D- and GND. Connect GND, D+ and D- to the Raspberry Pi, and additionally connect GND and +5 V from power supply to the same holes on USB-hub GND and V. Now there is common contacts: GND, D+ and D- between Raspberry Pi and hub needed to work, and additional power for USB devices, connected to the hub. Tested on my Raspberry Pi.


 * Anker
 * 7 Port USB 3.0 Hub, model AAH221 . Input is a USB 3.0 type A.  This hub uses an external 12V switching type power supply.   It does not function as a bus powered hub.  The hub does not backpower the Raspberry Pi, and appears to have complete isolation on the 5V lines between the input port and output ports.   The 7th port is a BC 1.2 spec port.  The manual status up to 2 A can be supplied on the charge port, when no other devices are connected.
 * With the hub powered and no devices connected, I measured the following voltages on the charge port: 5.19 V @ 0 A, 4.84 V @ 1A, 4.84 V @ 1.5 A, 4.75 V @ 2 A.   With power applied and no devices connected, I measure the following voltages on the ports : P0 (input) 0V, P1 5.24 V, P2 5.24 V, P3-P6 5.19 V, P7 5.19V
 * Power supply voltage is 12.3V with no load, 12.0 V with 1.5A load on the charge port.
 * Has been powering a Model 2 fine, have not yest tested heavily with USB devices.
 * Digitus
 * 7-port USB2.0 Powered Hub. Model DA-70226.
 * Eminent
 * EM1102 4 Port USB 2.0 Hub with 1 A power adapter. It's able to power the Raspberry Pi, external HDD and other peripherals.
 * EM1107 7 Port USB 2.0 Hub with 2 A power adapter. It's able to power the Raspberry Pi, external HDD and other peripherals.
 * Gembird
 * Gembird UHS 242 4-port USB 2.0 Hub (5V DC, 1A). NB: This is a 4-port switching hub that enables the "sharing" of up to four USB devices between two computers. Whilst it may be powered externally, it does take power from both connected computers. If one of them is, say, a netbook or laptop, that may provide sufficient extra power to enable the use of USB devices that the Pi alone cannot handle.
 * Genesys Logic (sold at Fry's)
 * Genesys Logic 4-Port USB 2.0 Hub (ID 05e3:0608) (Other brands include Gigaware, Hama and Belkin, same ID shows up in lsusb) - works, but increases packet loss problems
 * Genesys Logic 4-Port USB 2.0 Hub (ID 05e3:0606) (Other brands include i-Rocks, same ID shows up in lsusb)
 * Hama
 * Hama 4-way USB 2.0 Hub
 * Hama 7-way USB 2.0 Hub (identified as two "05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB" but Pi boots OK only with 1.2A power, not with 1A..)
 * HP
 * HP ZR2240w 21.5" Monitor with built in 2-Port USB Hub (B)


 * Laser
 * "7 port USB hub with AC adapter Version 2.0". 5 V 1 A (found at Harvey Norman Australia for $24.95 and Australia Post Shops for $9.95).  You can power the Raspberry Pi by connecting both the main USB connector to the Raspberry Pi USB port, and from a spare USB port back to the power micro USB socket.  If you don't do both, boot-loops are likely to occur.
 * Due to this hub back-feeding power, Model B rev 2 boards will occasionally crash with this hub connected (every 24 hours for one user). Model B rev 1 appear to be stable.
 * Logik
 * LP4HUB10 4-Port USB Hub. Throws errors when used with Fedora remix 14
 * Logik L4THUB10 4 Port powered hub works fine under Raspbian/Wheezy/model B. Captive USB cable, 2 A power supply, convenient single top mounted USB socket. Unlike my last hub, will power Wi-Fi!
 * LogiLink
 * UA0085 USB 2.0 Hub, 4-Port with PSU 5 V, 2 A
 * UA0090 USB 2.0 Hub, 4-Port with PSU 5 V, 2 A
 * UA0091 USB 3.0 Hub, 4-Port with PSU 5 V, 4 A. Connected with USB2.0 cable. 1 A per port, able to support USB HDD drives and other power hungry devices. Tested with kernel 3.1.9-cutdown, Wheezy.
 * UA0096 USB 2.0 Hub, 10-Port with PSU 5 V, 3.5 A (Not suitable for powering Raspberry Pi because it doesn't work unless there is working USB input present even with PSU plugged in.)
 * UA0160 USB 2.0 Hub, 4-Port with PSU 5 V, 2 A. Able to power the Raspberry Pi, keyboard, mouse and LogiLink UA0144 USB Ethernet adapter. (More testing to come.) Was not able to record audio properly via a Soundblaster Play! device. Tends to draw power from the Pi.
 * Macally
 * Hi-Speed 7-Port USB 2.0 Powered Micro HUB, AC Powered. Includes a 2000 mA wall-wart (US style)
 * Manhattan
 * (#160612) Hi-Speed USB 2.0 Micro HUB, AC Powered (identifies as ID 05e3:0608 Genesys Logic) Includes a 1000 mA w ll-wart (US style)
 * (#161718) MondoHub 28 Port USB 3.0 & USB 2.0 HUB (24 USB 2 ports @500 mA each) + (4 USB 3.0 Ports @900 mA each) Power Switches on each port, AC Powered and Includes a 5 V 4 A wall-wart (US style)
 * Newlink
 * NLUSB2-224P 4 port USB 2.0 Mini hub with PSU 5 V 1 A
 * NLUSB2-222P 4 port USB 2.0 Hub with 5 V 2 A PSU (Available From | ModMyPi)
 * Nilox
 * Nilox USB 2.0 4port HUB model HUB4USB2AC with PSU 5 V 1.0 A
 * Plugable
 * USB2-HUB4BC 4 Port USB 2.0 Hub with BC 1.1 Fast Charging. 5 V 2.5 A power supply. Powering Raspberry Pi via microUSB from a hub port. USB Audio peripheral tested and working.
 * USB2-HUB10S 10 Port USB 2.0 Hub 2.5 A power supply. Powering Raspberry Pi via microUSB from a hub port.
 * USB2-HUB-AG7 7 Port USB 2.0 Hub with 5 V 3 A power supply. There are US and UK power supply versions and it can be ordered in US and (for the UK version) many countries in Europe. There is a video showing this hub powering both the Raspberry Pi several peripherals at once. Confirmed to work with Element14 WiPi Wi-Fi dongle and Seagate external hard drive (simultaneously)
 * Pluscom
 * Pluscom 7 Port USB 2.0 Hub Model U7PH-3A with 3 A PSU. USB ID 1a40:0101. Powering Raspberry Pi via microUSB from a hub port. Internally two 4 Port switches linked. Leaks power back up USB data cable to Raspberry Pi, but it is not really a problem when powering Raspberry Pi at the same time.
 * Satechi
 * ST-UH12P 12 port powered hub with 2 Control Switches. Also works while powering the Raspberry Pi.
 * Staples (Business Depot) (Bureau EN GROS)
 * Staples 4-port hub Item 607477-CA
 * StarTech.com
 * StarTech.com 7-port Compact USB 2.0 Hub (ST7202USB). Comes with 5 V 2 A supply. Shows in lsusb as two Genesys Logic, Inc. USB-2.0 4-Port HUBs (05e3:0608). Back powers Raspberry Pi (just, voltage across TP1 & TP2 is a little low when powered from this hub).
 * SumVision
 * Sumvision Slim 4 Port High Speed USB 2.0 HUB with PSU 5 V 1.0 A (from | 7dayshop)
 * Sitecom
 * CN-032 4 Port USB 2.0 Pocket Hub. Works for powering the Raspberry Pi, an USB WLAN Adapter, wireless Kbd+Mouse. Using an 2500 mA Voltcraft
 * CN-060 4 Port USB 2.0 Hub powered with AC Adapter (1 A). Powering Raspberry Pi via microUSB from a hub port.
 * CN-061 7 Port USB 2.0 Hub powered with AC Adapter. There is a voltage problem on the left half of the hub (4 ports) that do not deliver enough current to feed a wifi dongle (tested with an RTL8191S); you should not use these ports for anything important (keyboard keys will stick, self-powered USB hard disk will reset continuously). The remaining 3 ports on the right half are instead working as expected.
 * Sweex
 * US014 4 Port USB 2.0 Hub
 * Targus
 * ACH81xx 7-port powered hub. 5 V 3 A power supply, with 2 high power ports. (possible conflicting behaviour with USB keyboard / Wi-Fi Dongles)
 * ACH63EU 4-port. Using a 5 V 2 A power supply, which isn't supplied with the hub, it is able to power the Raspberry Pi as well.
 * ACH67EU 4-port. Without an external power supply it can run at least keyboard, mouse and USB dongle.
 * The Pi Hut
 * 7 Port USB Hub (from The Pi Hut)
 * Trendnet
 * TU2-700 7 Port Powered USB 2.0 Hub with AC Adapter (5 V 2 A)
 * Tripp-Lite
 * U222-007-R 7 Port Powered USB 2.0 Hub with AC Adapter (5 V 2.5 A) Powering Raspberry Pi from the hub works.
 * Ultron
 * UHN-710 7-port powered hub with PSU 5 V, 3 A. USB ID 1a40:0201.
 * VANTEC
 * 4 Port USB 2.0 Powered Hub Model: UGT-MH304. 5 V 2 A AC/DC adapter. Go 2.0 Mini hub.
 * Z-TEK
 * Z-TEK 7-port powered hub with PSU 5 V, 4 A. USB ID 1a40:0201.
 * "Unknown"
 * 10(7-4) port hub idVendor=1a40, idProduct=0201 / idVendor=1a40, idProduct=0101 works

Problem USB Hubs
Please check known workarounds here before adding to the list


 * Addon
 * 7-Port Powered Hub - labelled ADDUH070P - Gives constant Eth0 errors on boot.
 * Belkin
 * 7-Port Powered Mobile Hub - device labelled F4U018, packaging labelled F5U701. lsusb reveals it to be two Genesys Logic 4-port hubs based on the GL850G chipset (vendor: 0x05e3 product: 0x0608) ganged together. Yields a lot of "handle_hc_chhltd_intr_dma:: XactErr without NYET/NAK/ACK" errors and device resets in /var/log/messages. Low speed devices such as keyboards work OK, Wi-Fi/mass storage is unreliable or broken. -- No error messages with the latest kernel, but it is still unstable with mass storage devices. Also, leaks current back to the Raspberry Pi (can be fixed by overtaping GND and +5 V pinouts)
 * F4U022 7-Port powered USB hub (powered 5 V, 2.6 A), same as F4U018
 * 7-Port Powered Hub - device labled F5U237 Rev.3 - ID 050d:0237 Wired Ethernet fails to connect; gives "DWC OTG HCD URB enqueue failed adding QTD. Error status -4008" Result is same as DUB-H7 below.
 * F5U404 Hi-Speed USB 2.0 4-Port Mobile Hub. Faulty/bad design; Leaks current back up the cable to the Raspberry Pi.
 * F5U307 Hi-Speed USB 2.0 7-Port Hub (Powered, able to apply power to Raspberry Pi via micro USB from this hub at same time) It work's sometimes. (Works always without powering the Raspberry Pi, haven't tried that)


 * Dell
 * Dell U2410 Monitor Built-in 4 Port Hub - Shows up as a pair with 0424:2514 and 0424:2640. Standard Microsystems Corp. USB 2.0 Hub. When connecting some devices it kills the Ethernet with "smsc95xx 1-1.1:1.0: eth0: Failed to read register index 0x0000011X" errors. It did work for a keyboard and webcam. Bluetooth that works connected directly to the Raspberry Pi triggers the error.


 * DELTACO
 * 7-Port USB Hub UH-713 Rev 3. This one consists also of two 05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUBs connected together. The power supply is rated at 5 V 2 A. It kills Ethernet when X11 is started.


 * Digitus
 * 4-Port USB Hub, no special designator. Chip inside is a GL850G, lsusb identification is 05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB. The hub comes with a 5V 2A PSU that is quite capable of powering the Raspberry Pi and additional peripherals. I did not test whether the hub feeds power into the uplink USB port. The problem with this hub is that USB sticks connected to it reliably disconnect after a short time of writing to them (via cat /dev/zero > /dev/ ). Sometimes they reconnect with a different device, sometimes they do not. The only error messages in the logs are plain vanilla USB device disconnects. While this may look like a power-issue, measurements with a digital oscilloscope found absolutely no problem. Another observation I have made is that sometimes (not always), the data-transfer rates to the USB sticks slow down to about 500kB/s. I suspect this is a problem with the USB driver that does not manage to work around some brokeness in the hub chip. The hub has no current-limiter at all and plugging in some peripherals will hard crash your Raspberry Pi, something I do not observe with better hubs.


 * Dynex
 * 7-Port USB Hub - Does not work in Debian 19-04 image.
 * DX-HB7PT 7-Port USB Hub - As per the Gear Head below, it's 2 daisy-chained Genesys Logic 05e3:0608 devices. Appears to result in significant slow downs when the USB is under load, such as running the root file system from a USB drive.


 * Dynamode
 * 7-Port USB 2.0 Hub (Silver and black). Feeds power back up the interconnect to the Raspberry Pi causing the power LED to light on the Raspberry Pi if the hub is powered on, but the Raspberry Pi is not. The Raspberry Pi also fails to boot when powered off this hub, with or without the interconnect plugged in. Stops the network from working when connected to the Raspberry Pi after booting the Raspberry Pi - cannot ssh to the Raspberry Pi. Best avoided. :-( Shows up in lsusb as a pair of ID 05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB which is interesting. - Confirmed. This hub also appears unable to power an external USB drive using a y-cable as it gives the error -71 message in dmesg (when providing external power to the Raspberry Pi).
 * 4-Port High-Speed USB 2.0 Hub (USB-H40-A2.0), came with with a 1 A power supply. Leaks power to the Raspberry Pi through the uplink. Doesn't work with Raspberry Pi, unless the Raspberry Pi is powered by a second power source. This hub is completely generic and I've seen it being sold under different brand names as well. Therefore, a picture is included for easy identification.


 * D-Link
 * 7-Port USB Hub DUB-H7 Rev. C (Crashes USB stack/complete Kernel, including Ethernet, when plugging / using some peripherals). (See note above, it works with some distros and/or with latest firmware). Revision B is working perfect. The version C is completely unuseable with PI. When connected while booting the kernel hangs during boot. When connecting later it seems works. Can be used for powering PI only when it is not connected to the PI as USB root node. When this is done the ports do not provide any power. I assume this is caused by the reset logik that turns of power when an usb reset is given. When the HUB is connected to a PC while powering the PI the PI has also a power loss.


 * E-Solution
 * 4-Port 2 A Supply (Does not detect at all during boot or after boot- no messages) [IC = Alcor Micro Corp (AU6254)]


 * Fosmon
 * 7-Port USB 2.0 Hub with 1 A Power Supply (Causes interference with other USB devices and sends enough power to light up the Raspberry Pi with it's Micro USB cable unplugged).


 * Gear Head
 * UH7250MAC 7-port powered hub. Internally, two daisy-chained Genesys Logic 05e3:0608 devices. Causes Ethernet instability when used under very specific circumstances, in X11.
 * UH5200T 4-port powered hub. As of 2012-08-16 Wheezy, if any USB 1.x device (a keyboard, for example) is plugged into this hub, Ethernet stops, and USB interrupts for other devices get dropped (keys repeating forever), etc. Occurs even if power is not attached (not a power leakage problem).  Appears working after a bootloader and/or firmware update on 9/12.  Also, turned out to be somewhat more specific to the combination of two particular low-speed devices.
 * UH5500ESP GearHead 4 Port Hub with Energy Saving Power Switch (5 V, 1 A)- External power and input 5v lines are connected together before the power switch, resulting in back feeding. There is no diode. To make it compatible, remove the board, cut the trace between the diode pads (D1) and install a 1a surface mount diode. As an alternate you can just cut the trace and it will require external power. The ic will still be powered from the bus because there is a second trace from the 5v input. Front of PCB Back of PCB Location to cut trace


 * Hama
 * 4-Port USB 2.0 "bus hub", model 78496 (?). Only works for low power devices (card readers?), but it does not work for power hungry devices (HDD and WLAN). It doesn't boot when hub connected to Raspberry Pi. The funniest thing is that Raspberry Pi powers on when I plug in this hub to normal size USB port (not that small dedicated port). idVendor=05e3, idProduct=0608


 * Kensington
 * 7-Port Dome Hub model no 1500129 (Possible problems with malfunctioning keyboard, kills mouse when GUI started).


 * iBall
 * Piano 423 4-Port USB hub. Listed in lsusb as Genesys Logic. Fails to deliver enough power to connected devices even when using AC power supply.


 * ISY
 * Active 7-Port USB Hub model IHU 3000. Connecting Pi as specified below will cause the hub to lose 4 of its 7 ports, seen on 2 new items both from Media Markt. At first it works, showing as 2 times "Genesys Logic, Inc. USB-2.0 4-Port HUB". After a few reboots, one of the two disappeared.


 * Inland
 * 4-Port USB 2.0 Cable Hub model no 480426 (Some devices work, some don't, cheap unshielded untwisted wire design)
 * 7 Port 2.0 Hub UPC 837654142967 Unable to provide power with stock AC adapter, poorly soldered, eventually fried.


 * Logik
 * LP7HUB11 7-Port USB Hub. (Ethernet failed, slow response, in LXDE. Happened whether or not the hub's independent power supply was connected to the hub.)


 * LogiLink
 * 7-Port powered USB-Hub with switch UA0124. Does not work even with a x86 Linux box. Does work with Windows and comes with a beefy 3,5 A power supply that works with a Belkin 7-port mobile USB-Hub to power a cluster of 4 Raspberries.
 * LogiLink USB 3.0 Hub 4-Port with 2A Power Supply. 2109:2811. Detectes and crashes during boot. mmc0: Timeout waiting for hardware interrupt, mmcblk0: error -110 sending status command, cannot find and mount root, kernel panic.


 * nGear
 * nGear G-H508 Mini 4 Port USB2.0 Hub. Does not work when more than 1 device is plugged in even with power supply.


 * Soniq
 * 4-Port 5 V supply. Model number CUH100. (B). Appears to draw power away from the Raspberry Pi, even when the Raspberry Pi has an isolated power line. Netgear WNA1100 Wi-Fi Adapter (which is known to work in other setups is recognized, but it is unresponsive).


 * Targus
 * ACH115EU 7-port powered hub. 5 V 3 A power supply. Arduino communicates with Raspberry Pi when connected directly to Raspberry Pi's USB port, but it hangs as soon as if connected via ACH115. Also sometimes smsc95xx eth0 Failed to read register index 0x00000114 etc. errors in syslog when used.


 * TCM
 * Model 234298 s/n T634007737 powered hub. 4 ports plus card reader. 1 A power supply. Model B, Wheezy Raspbian works OK with keyboard/mouse, but there are problems with Wi-Fi no connects. (insufficient power?)


 * Trust
 * 10-port USB 2.0 Hub (powered). Prevents Ethernet from being recognised.
 * SliZe 7 port USB 2.0 Hub (powered) - Item number 17080 (Barcode 8 713439 170801). Prevents Ethernet from being recognised. Keyboard sends multiple characters.


 * Unbranded / Multiple Brands
 * 7-port silver/black hub. Also sold elsewhere under brands such as 'EX-Pro', 'Trixes' and 'Xentra' -- This is probably due to an inadequate power supply. -- I replaced the terrible power supply with a very good one, kept getting "DEBUG: handle_hc_chhltd_intr_dma:: XactErr without NYET/NAK/ACK" in dmesg, with no devices plugged in to the hub (with or without the power supply in). Measurements by TrevorGowen (talk) of the power loading behaviour of an example of this type of hub and its supplied PSU are logged at CPM-Spectre-Pi...PoweredUSBHubs, together with similar measurements of other devices.
 * Generic 7-port black hub with Genesys Logic GL850A chipset
 * Cerulian 10 Port USB 2.0 Top Loading Hub with 2 A supply (kills mouse and network port)
 * USB 2.0 4 PORT INT/EXT DUAL HUB BAY -- Genesys Chipset -- idVendor=05e3, idProduct=0607 -- low speed devices worked, but there are strange USB failures when X session started. High speed devices such as hard drives had failures.

USB Hub Power Hookup


A powered USB hub is required to attach high power USB devices to the Raspberry Pi. In this case it may be desirable to power the Raspberry Pi from the USB hub instead of in the usual manner from a separate power supply. This power hookup requires two USB cables between Hub and Raspberry Pi, which are both shown on the power hookup schematic. The cable on the left side supplies power and that on the right is a standard USB cable that would be required to connect the Raspberry Pi to any USB hub or other USB device.

The schematic also shows two important features of the USB hub internal power wiring that are required to correctly power the Raspberry Pi. First, the hub coaxial power input directly connects to the USB A output ports. This allows the Raspberry Pi to skip the usual process of asking the hub to switch it from a 100 mA low power to a 500 mA high power device and to exceed even this high power limit so that it can meet its typical power requirements of 700 mA or more. Second, the hub diode prevents back-powering, that is, current cannot flow in the reverse direction from the hub coaxial power connector back out to the micro B input port and into the Raspberry Pi.

USB hub power circuitry tests
This section describes two tests that will verify that a USB hub has the correct power circuitry.

Equipment
In addition to the USB hub, Raspberry Pi, and high and low power load resistors, these tests require a digital voltmeter and 3 patch cords, one of each which terminates on one end with a coaxial power plug, a USB A plug, and a mini B plug. It's possible to power all tests from a coaxial jack connected to the hub power adaptor coaxial plug, but it will be more convenient to use a standard bench power supply with voltage readout and adjustable current limit.

Output power test


The output power test has two parts, which are both shown on the output power test schematic. The setups for both parts require a 5 &Omega; load on a hub output port, which simulates a 1 A current drawn by a Raspberry Pi and perhaps some attached peripherals. A 10 W rated load resistor would provide a safe margin over the 5 W power it must dissipate. The setups differ in how the 5 V power is provided to the hub's coaxial power input. The first and simpler setup powers the hub directly from the hub power adaptor and verifies that in its normal operating configuration the hub will provide sufficient power. As shown on the schematic there must be at least 4.75 V across the 5 &Omega; load resistor, which is the minimum voltage required to power the Raspberry Pi.

The second setup also powers the hub through the coaxial input, put provides electrical access to the +5 V and ground conductors of the coaxial power plug. This is most easily accomplished with a bench power supply and coaxial power plug patch cord. A bench power supply will provide digital readout of both voltage and current, for which a 1 A reading guarantees that the required test current is properly flowing through the 5 &Omega; load resistor. Measure the ground leg voltage drop between the barrel patch cord wire of the coaxial power plug and the pin 4 wire of the type A output plug and the +5 V leg drop between the central wire of the coaxial plug and the pin 1 with of the output plug. Under the 1 A test conditions both of these legs should see a voltage drop of the order of 100 mV and their sum should be less than about 250 mV as is indicated on the schematic. Double-check that this sum plus the drop across the 5 &Omega; resistor (measured between pin 1 and 4 patch cord wires of the type A output plug) equals the bench power supply voltage. The comparable 100 mV drops on both ground and +5V legs confirms that the hub internal power wiring directly connects the power supply to the USB output ports.

Input diode test


Patch cord the test circuit as shown on the input diode test schematic. This test simulates the hub in bus-powered mode. The rational for selecting a 50 &Omega; load resistor is that it will draw a nominal 100 mA current, which corresponds to 1 load unit in the USB 2.0 specification and equals the maximum power available to a device on a bus-powered hub. The specification also requires that such low-power devices have a minimum operating voltage of 4.4 V, which means that even with the 0.4 V diode drop the hub will supply sufficient voltage. The diode voltage drop can be measured between the pin 1 patch cord wire of the mini B input plug and the pin 1 wire of the type A output plug or calculated as the difference between voltages measured across pin 1 and 5 wires of the input plug and pin 1 and 4 wires of the output plug. The presence of the 0.4 V drop between hub input and output is strong evidence that the USB hub circuitry includes a diode that prevents back-powering the Raspberry Pi.

A setup very similar to the output power test can check for reverse leakage current and further strengthen the evidence that the hub internal circuitry includes a diode at the position indicated in the test schematic. As shown on the output power test schematic power the hub through its coaxial power input and optionally put the 1 unit power load resistor on an output port. First verify that the voltage across the pin 1 and 5 patch cord wires of the mini B input plug is very nearly 5 V. This is consistent with a high voltmeter impedance limiting both the reverse leakage current and reverse bias voltage to a very small values. Next add a 100 k&Omega; resistor across the pin 1 and 5 wires of the mini B input plug and again measure the voltage. Assuming the voltage is now in the 100 mV range, the voltage drop across the diode is very nearly 5 V and Ohm's law gives the current through the resistor in the 1 &micro;A range. This is the diode leakage current at a 5 V reverse bias. If necessary adjust the mini B input plug load resistance to get a voltage drop across this resistor in the 100 mV range and calculate the leakage current accordingly.

Example: Plugable 7 Port USB Hub USB2-HUB-AG7
The Plugable 7 Port USB Hub model USB2-HUB-AG7 passes both the above power circuitry tests and is suitable for powering the Raspberry Pi. Here are the measurements:


 * 1) Output power test
 * 2) * Adapter power
 * Voltage drop 5 &Omega; load: 4.91 V (982 mA load current)
 * 1) * Power loop voltages (952 mA load current)
 * Supply: 5.00 V
 * +5 V leg: 133 mV
 * 5 &Omega; load: 4.76 V
 * Ground leg: 115 mV
 * 1) Input diode test
 * 2) * Forward bias
 * Diode voltage drop: 0.37 V (93 mA forward current)
 * 1) * Reverse bias
 * Diode leakage current: 1.47 &micro;A (5 V reverse bias and 147 mV drop across 100 k&Omega; reverse bias load)