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9.0 VS, Power Supply

Supply Voltage: 4.75 - 5.25 volts (5V ±5% Regulated)

Supply Current:  300 mA Max

Normal Power Connector: USB-B Receptacle

Typical Power Supply:  Any USB-Style Supply

VS Voltage:  Equal to Supply Voltage

VS Max Current:  200 mA (500 mA - Supply Current)


VS Terminals

The supply voltage (described in next section) goes through some protection circuitry and then is presented on the VS terminals.  The VS terminals are designed as outputs for the supply voltage.  The supply voltage is nominally 5 volts and typically provided through the USB connector.

All VS terminals are the same.

The VS connections are outputs, not inputs. Do not connect a power source to VS in normal situations.

The max total current that can be drawn from VS is 500mA - DeviceSupplyCurrent, so if the T7 needs 300mA to run, that leaves 200mA available from the VS terminals. 

The voltage on VS can be noisy and can change unexpectedly. Circuits that are sensitive to changing or noisy supply voltage, such as bridge circuits, should not be supplied from VS.


Measuring Current Draw

One way to measure how much current the T7 is drawing is by measuring the voltage across R15.  R15 is a 0.1 ohm resistor, so if you measure 0.025 volts, that means the current through the resistor is 250 mA.  R15 is a large resistor located on the top of the PCB just behind the green LED.  To measure the voltage across R15 connect the positive lead of your meter to the test point "Vhost" and connect the negative lead of your meter to the test point "Vs".

R15 is in series with the 5 volt supply from the USB connector.  If powering from J5 (see "Alternate Power Supply" in the OEM section) use R21 instead.  The "Vs" test point is also the negative for R21, but there is no positive test point so you just have to touch the upstream side of R21.

Note that the "Vs" test point is actually the Vsupply bus described under "J5 - Alternate Power Supply" in the OEM section, and technically not exactly the same as the "VS" bus documented in this section.


Power Supply

Power supply for the T7 is typically provided through the USB connector.  For a different board-level connection option see "Alternate Power Supply" in the OEM section.  Typical power supply sources include:

  • USB host or hub.
  • Wall-wart power supply with USB connection (included with normal retail units ... not OEM).
  • Power-over-Ethernet splitter (e.g. TP-Link TL-POE10R with Tensility 10-00240 with Tensility 10-00648).
  • Car charger with USB ports (e.g. Anker 71AN2452C-WA).
  • Rechargeable battery with USB ports (e.g. Anker Astro E5 79AN15K-BA perhaps with Belkin F3U133-06INCH).
  • Battery with car charger (e.g. Anker 79AN15K-BA with 71AN2452C-02WA).
  • Battery with solar panel (e.g. Anker 79AN15K-BA with 71ANSCP-B145A).
  • Pigtail a cable with a USB-B connector to get at the red & black wires, and make some sort of custom cable for your 5V power supply.

The supply range for specified operation is 4.75 to 5.25 volts, which is the same as the USB specification for voltage provided to a device.  Nonetheless, we have seen some USB host ports providing a lower voltage.  If your USB host port has this problem, add a USB hub with a strong power supply.

See information about Power over Ethernet (PoE) see the PoE App Note.

See related data in the General section of Specifications.

Normal retail units (not OEM) include a 5V, 2A wall-wart style power supply:

CompatibilityMakeMfr. Model No.
North America VA-PSU-US1 JX-B0520B-1-B
Europe VA-PSU-EU1 JX-B0520A-1-B
United Kingdom VA-PSU-UK1 JX-B0520C-1-B
Australia - JX-B0520D-1-B
China - JX-B0520H-1-B

Note that the JX-B0520 supply is rated for 0 to 40 deg C operation.


Some VS Terminals Not Working?

We sometimes get a report that some VS terminals on a device are not working, but this is rarely (never) a real problem.  If the device has LED activity or you can talk to the device, the VS terminals almost certainly do have a reasonable voltage on them.  The problem is sometimes using a bad DMM (low battery?), but the most common problem is touching DMM leads to the screw heads of loose terminals.  The screw head is often a valid contact point when the screw terminal is fully clamped down, but the only guaranteed valid connection is to clamp a conductor securely inside the screw terminals.