2.3 - Vext (Screw Terminals and Power Jack) [UE9 Datasheet]

There are two connections for an external power supply (Vext): a two-pole screw terminal or a 2.1 mm center-positive power jack. These connections are electrically the same, so generally only one is used at a time. The nominal power supply voltage for the UE9 is 5 volts. Power can be provided from the USB connection (Vusb) or an external power supply (Vext). The UE9 has an internal semiconductor switch that automatically selects between Vusb and Vext. Both power sources can be connected at the same time, and either can be connected/disconnected at any time. As long as one supply remains valid, the UE9 will operate normally. If both Vusb and Vext are connected and valid, the internal switch will select Vext. The UE9 power supply requirement is nominally 5 volts at <200 mA (see Appendix A). This is generally provided by a wall-wart or wall-transformer type of supply. A supply capable of 500 mA is recommended. The power jack connector is 2.1 × 5.5 mm, center positive. A linear (regulated) or switching supply is acceptable. Switching supplies are generally noisier than linears, but the UE9 is not particularly sensitive to power supply noise, and most users will not notice any difference. One option is the CUI EMSA050120K-P5P-SZ available from Digikey, for which you will also need a clip: EMS-AU (Australia), EMS-CC (China), EMS-EU (Europe), EMS-UK (United Kingdom), or EMS-US (United States). A newer option is the CUI SMI6-5-K-P5, where K means no clip but you can also order with different clips (uses the same EMS clips mentioned previously). Another interesting option is a power-over-Ethernet (POE) adapter. The UE9 does not support POE itself, but there are POE adapters that split out the data and power in such a manner that is acceptable for the UE9. These adapters consist of an injector and splitter, and a single Ethernet cable carries data and power between the two. LabJack Corporation has done testing with the WAPPOE unit from Linksys, which is an off-the-shelf POE adapter with the proper connections for a UE9.