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Thread: Teensy 3.2 external power confusion

  1. #1

    Teensy 3.2 external power confusion

    I've read several threads that almost answer this but not quite... Probably a dumb question, but this is my first time building a project with a Teensy using 3.3v pins...

    I am concerned that the 250mA limit on the 3.3v pin from the Teensy might get exceeded at some point if all the LEDs in my project are on at once , so I would like to give the Teensy more external power. In other projects this was simple: attach a 5v power supply to Vin, cut the pads to the USB power

    I had planned to do the same here, but the limit on the voltage regulator means it won't actually help I assume?

    I'm probably being stupid, but how do you get more current available without going through the voltage regulator which limits it to 250mA?

    pretty sure i'm missing something elementary here, so please be gentle pointing it out!

    (actually: I just made a bunch of current draw measurements on my components and actually I think I might be fine with 250mA, but I'd really like to know the answer to this for the future...)

  2. #2
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    Not the expert on this … but one way is to get 5V on VIN from a trusted supply and then with that and common GND - the LED's would be fed from the same 5V stepped down or whatever as need to feed things not able to be powered from the Teensy.

    I got a PCB with 32x32 RGB matrix that was set up that way using a 2A supply the Teensy got what it needed and with common GND was able to talk to the rest of the board that powered the LED's.

    The 250 mA is not a hard limit as the regulator can do 'some more' as long as it can run cool enough and there is a poly fuse that will show itself when needed ideally allowing it to force a time out notice.

  3. #3
    Senior Member
    Join Date
    Oct 2015
    Roma (IT, EU)
    Quote Originally Posted by the_duckchild View Post
    I'm probably being stupid, but how do you get more current available without going through the voltage regulator which limits it to 250mA?
    You may just add your own regulator of choice (like a MP1584, just to name one), and use it to power both the Teensy via Vin (cutting VUSB pad) and the LEDs.
    In other words, don't feed the LEDs from the 3.3V pin of the Teensy, but directly from the (external) regulator.

    Attach the regulator to the DC source. Set the regulator to 3.3V out.
    Start two rails from this 3.3V output.
    One goes to Teensy Vin (disregard specs which say it needs 3.6V min: works fine at 3.3), the other goes to LEDs.
    3.3V pin on Teensy is left unused.
    A MP1584 can source 1.5A without issues. 2.5A with heatsink.

  4. #4
    thank you both, I knew it was easier than I was making it in my head!
    That makes absolute sense, I was having a total mental block - also knowing the Teensy will run at 3.3v definitely makes it simpler!

    I think USB should actually provide enough power this time, but it was frustrating not being able to see the answer, and this will definitely come in handy in the future!

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