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Thread: teensy 3 and external power

  1. #1
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    teensy 3 and external power

    hi!

    here is a description how to setup teensy2 to work with external power:
    http://www.pjrc.com/teensy/external_power.html

    i am interested in option #3..
    but where do i have to put the diodes on the teensy3 and where has the catode to face?

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Are you going to use a 3.3 volt power supply, or a 5V power supply? It matters with Teensy3.

  3. #3
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    Quote Originally Posted by PaulStoffregen View Post
    Are you going to use a 3.3 volt power supply, or a 5V power supply? It matters with Teensy3.
    i want to use 5V power supply

  4. #4
    Senior Member PaulStoffregen's Avatar
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    The simplest way is to just cut the pads apart on the bottom side, as shown on back side the reference card. Then you can connect 5V to VIN. The USB will be unable to power the board.

    If you want the diodes to allow either, then solder a diode between those cut-apart pads, or between the VUSB and VIN pads. The cathode (side with the stripe) connects to VIN. Use a diode between your power supply and Teensy3, also with the cathode connected to VIN. With the 2 diodes, the Teensy3 will get power from either source, but neither can feed current back into the other.

  5. #5
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    Paul ,
    There are two pads on the backside ..Do you cut them both on the Teensy3 ?.......and ...If I power up with a 5v external can i still load the sketches via USB...and...will i pick up 5v output now on the 3v pins

    Tks Mike

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by Maxx1 View Post
    There are two pads on the backside ..Do you cut them both on the Teensy3 ?


    .......and ...If I power up with a 5v external can i still load the sketches via USB
    Yes.

    ...and...will i pick up 5v output now on the 3v pins
    No. The outputs will still be 3V. If you check the Teensy3 schematic, this change just disconnects the 5V from USB and powers the board from your 5V at VIN. Everything else runs exactly the same way.

  7. #7
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    Fair enough Paul. You see I am trying to get the 5volts out of the teensy3 since i have been successful lighting up the DOg163 LCD. If, on the other hand, I can only get 3.3volts out then I may have the same problem. That is the reason I posted here.

  8. #8
    Senior Member PaulStoffregen's Avatar
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    I've got that dogm163 message open in another window... one a few (more involved issues) I intend to look into later today. First, I need to dig out the test board where I used one of those displays and see what I did with it.

  9. #9
    For my understanding, according to this link: http://www.pjrc.com/teensy/pinout.html is it possible to feed 5V directly through Vin even if the two pads are not cut.
    Or should one cut the both pads in every case?

  10. #10
    Senior Member PaulStoffregen's Avatar
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    It you don't cut the pads apart, then VIN and VUSB are still connected together. If you ever connect external 5 volts and a USB cable at the same time, the USB could attempt to feed current into your 5V power supply, or the power supply could attempt to drive current back into your computer. Neither of those is a good thing. Which direction the current flows depends on which has higher voltage. The current does go through the 500 mA PTC "fuse" (which is really only a resistor that increases in value when it gets hot from too much current), so that does help limit the opportunity for damage. But still, it's not good to allow 2 power sources to attempt to drive each other. That's why Teensy3 has those pads, so you can cut them apart for these types of situations.

  11. #11
    Incidentally, Paul, if the power supply were to be a regulated 3.3v input, would you wire the same way (with cut pads and diodes) but supply input power to the 3.3v pin on the Teensy 3.0?

  12. #12
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    I am working on a battery powered data logging application. I will be using a lion battery as power source, which will be charged over the usb connector. Basically this is nothing special and this kind of setup has been discussed here in several posts. I just might have a suggestion for an improvement to your superb board: for application which require to be powered by an external source over vin, but also in case of a usb connection by vusb, you could move the solder jumper between the two anodes of the allready installed diode. Now several setup are possible:
    1 - jumper closed (not cut through) is just the same as now
    2 - with the jumper open the board can either be powered by usb or vin.
    Now this is not so new, but has the benefit, you wouldn't have to add extra diodes externally which add extra voltage drop (which may make single lion cell applications harder ). The allready placed diode should be able to handle the power disipation on just one diode, probably you would have a slight increase in voltage drop, but this would be much lower than having 2 diodes in series. Basically it would be no change in the BOM, but only a layout job.
    Another suggestion would be placing a voltage divider from vusb to an digital pi, so one could detect if usb is plugged in. In my use case, this would help me have the board run in low poer modes while gathering data away from the usb host, and switching to full performance when retrieving data with a usb connection.

  13. #13
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    Paul
    Can you please send the part number this PTC called D1 on your schematic?
    Thank you for your great help and support

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