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Thread: Teensy usb powered + External power at same time?

  1. #1
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    Teensy usb powered + External power at same time?

    Hello,

    So I've been reading some things on here and I don't quite understand some of it.
    Is it possible to have my teensy powered from a regulated 5V source (VIN), and then I plug on a usb cable to update it?
    Is it possible to do this OK without cutting the trace?


    I've done this with arduino nanos and got away with it, what's the issue with teensy?

    Teensy 3.6

  2. #2
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    if your external source voltage backfires to your PC port, it may or may not work, however, if the voltage of the external psu is higher you can blow out the PC usb port. Secondly some arduinos switch to the external power instead of USB if the power if both are applied, they have a circuit for that, not sure on the nanos, however, the VIN on teensies is tied to both external and USB, thats why a trace is there to be cut or not.

    you can also use a data-only usb cable as well instead of cutting the trace, this will allow you to reprogram teensy while plugged into the external source without cutting the trace. But realistically, you’d want to remember that later on in future you don’t use wrong usb cables or forget you didnt cut the trace, etc.

  3. #3
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    And is there a diode between the USB and the VIN?

  4. #4
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    https://www.pjrc.com/teensy/external_power.html

    option #3 is of interest to you

  5. #5
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    THanks. Wonder where this is on the 3.6.
    Tomorrow I search or if anything i come back here.

  6. #6
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by donperryjm View Post
    THanks. Wonder where this is on the 3.6.
    Tomorrow I search or if anything i come back here.
    On Teensy 3.x and LC the VIN<>VUSB cuttable trace is shown on the card - the same on them - but different than that web link to the Teensy 2.

  7. #7
    Senior Member+ MichaelMeissner's Avatar
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    Quote Originally Posted by donperryjm View Post
    THanks. Wonder where this is on the 3.6.
    Tomorrow I search or if anything i come back here.
    On all Teensy LC/3.0/3.1/3.2/3.5/3.6's, it is in the same place (and different from the Teensy 2 as defragster notes):

  8. #8
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    OK. I saw that circuit, and I'm still thinking of an easier way,

    So backfeeding is a concern, OK i hear that.
    Will it still be a problem if i put a diode after my regulator to drop the voltage to 4.3V, would that still backfeed into the usb 5v power?

  9. #9
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    Simulating this in multisim looks promising. What am i missing here?
    Last edited by donperryjm; 02-28-2019 at 02:38 AM.

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