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Thread: Powering teensy 3.5 from external power

  1. #1

    Powering teensy 3.5 from external power

    hi, i have a little question about powering the teensy from an external power supply . Is about cutting the track between vin and vbus, if i'm not gonna program the board while is connected to the external power, do i have to cut this track ?

  2. #2
    Senior Member+ defragster's Avatar
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    No cutting the trace is not needed: If you can remove external power for USB programming, then powering it without a USB connection with external power will not be a problem.

    Once you cut the VUSB trace it cannot be programmed without external power being applied - or the trace re-soldered. I did it to 1 each of 4 Teensy types - all have female headers - so I just added one single header pin in the VUSB hole and with a jumper wire to 5V and that VUSB pin I can go back to normal power and program with USB - or pull the wire and use external power.

  3. #3
    There are fancy ICs that allow automatic power source switching, but a simple jumper is the best. During the development I run both Teensy and my board from the USB power 90% of the time (jumper ON).

  4. #4
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    TPS2113A Power Multiplexer Carrier with USB Micro-B Connector.
    The TPS2113A makes a great addition to any project that needs to be able to transition between two sources like USB and external power
    https://www.pololu.com/product/2596

  5. #5
    The best place for such mux is Teensy itself. Then there is no need to cut the trace host/device. But the pin functions change slightly - Vin to external power input only and Vusb to Vout (mux output). Would be neat. TPS2113A is a bit restrictive on voltage though, fresh 4xAA could be a bit higher than 6V. I use high side switches with 6.5V max to turn on/off parts of the circuit.

  6. #6
    Sorry for bringing up this old post but I don't seem to be able to program my teensy 3.6 when external 5v is applied, my laptop doesn't see it unless I power from the 5v of my laptop, for programming I removed the red wire in my programming cable, I'm using an alienware 17 I'm wondering if it's my laptop

  7. #7
    Quote Originally Posted by Chriss_russell View Post
    Sorry for bringing up this old post but I don't seem to be able to program my teensy 3.6 when external 5v is applied, my laptop doesn't see it unless I power from the 5v of my laptop, for programming I removed the red wire in my programming cable, I'm using an alienware 17 I'm wondering if it's my laptop
    Sounds like your laptop can't give enough milliamps to power your teensy

  8. #8
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by Chriss_russell View Post
    Sorry for bringing up this old post but I don't seem to be able to program my teensy 3.6 when external 5v is applied, my laptop doesn't see it unless I power from the 5v of my laptop, for programming I removed the red wire in my programming cable, I'm using an alienware 17 I'm wondering if it's my laptop
    I saw something like this when it was connected to an RGB Matrix with a T_3.6 - even with the trace Vin<>VUSB cut under external power - the problem went away when I improved the ground path from the display to the external power. The weak GND to the external power was apparently causing the display to abuse the USB return GND path and disturbing the ability to program. Putting another GND to the Matrix external power stopped that. I know it stopped as the return GND through USB was measured at over 1 AMP before I added that - then programming the Teensy started working normally.

  9. #9
    Thnx for the reply @emielcpNL no if I connected and use power of my laptop it powers up fine and programs fine ...the issue is with external voltage

    @defragster I will check for grounding issues...note though I dont use VIN for external power I apply 5v to VUSB and apply ground, I then use a USb cable with power cut to try to program

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