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Thread: How to external power Teensy 3.6 and switch between USB power and external?

  1. #1

    How to external power Teensy 3.6 and switch between USB power and external?

    From what I understand, I can connect a diode between VUSB and VIN (?) to have the Teensy automatically use the higher voltage (USB power vs external), but I'm planning to use a 5v external power source.

    Is it possible to have a 5v external power source and ALWAYS use that if it's connected but otherwise use the USB power? That would help me during development, but when I move the device into "production" I'd like to power it using external power (but keep USB connected for data).

    Thanks

  2. #2
    Senior Member
    Join Date
    Jun 2013
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    Sure. Cut the trace between the power pads on the bottom of the Teensy, then solder your diode to those pads.

  3. #3
    Senior Member
    Join Date
    Dec 2013
    Posts
    264
    You can try this:
    FPF1320 Power Multiplexer Carrier with USB Micro-B Connector
    https://www.pololu.com/product/2594

  4. #4
    I can confirm potatotron's idea.
    I've been using Schottky diodes with my teensy 3.2 within a power supply, to power the teensy either from the board or from the USB. It works great and you can plug/unplug the cable even with the board on.

    If you want to prefer the USB over the external power you can use two diodes, one with a greater forward voltage than the other, D1 from VUSB to Vin and D2 from 5V to Vin. If the forward voltage of D2 is say 0.5V and D1 is 0.3V that'll cause VUSB to be used unless VUSB is 0.2V less than 5V.

  5. #5
    OK, let me make sure I understand correctly.

    I can use a single 1N5817 diode between VUSB and VIN, and it will always prefer my external power source even if USB and external are both 5v?

    Is this because the diode voltage drop (0.45v in my above link) causes the VUSB to only be ~4.55v so because my external power supple 5v is greater than 4.55v, it will be preferred?

  6. #6
    Ah yes, my apologies, my answer is the wrong way round!
    Only a single diode is needed if you're preferring an external power source applied to Vin

  7. #7
    Thanks very much!

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