Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 6 of 6

Thread: Teensy 3.2 Power Regulator

  1. #1

    Teensy 3.2 Power Regulator

    Hi everyone,

    a have two quick questions regarding Teensy 3.2's current draw and voltage regulation.
    In my project I am using a 78L05 power regulator (TO-92 package) to regulate 12V to 5V (plus two capacitors), connected to Teensy's VIN. Everything is working, but the regulator is getting quite hot So I was wondering:

    1) How much current is Teensy 3.2 typically drawing? I found multiple info ranging from 45 mA to 250 mA (btw: is there a way I could measure that myself?)
    2) The 78L05 is rated for 0,1 A. I am going from 12V to 5V. Do you think it is safe to use it together with Teensy 3.2?

    I searched the forum and couldn't find a definitive answer *hope it's okay I started a new thread.
    Thanks in advance!

  2. #2
    Senior Member
    Join Date
    Jul 2020
    Posts
    1,368
    The problem is the 78L05 can't dissipate much heat as its a tiny TO92 package, normally
    good for 0.25W or so.
    There are clip-on heatsinks for TO92, which could improve things, but if you are dropping
    all the way from 12V to 5V a switching regulator might be more reasonable - any linear
    regulator is only going to be 41% efficient for that voltage range, switching regulators are
    typically 80 to 90% efficient.

  3. #3
    Quote Originally Posted by MarkT View Post
    The problem is the 78L05 can't dissipate much heat as its a tiny TO92 package, normally
    good for 0.25W or so.
    There are clip-on heatsinks for TO92, which could improve things, but if you are dropping
    all the way from 12V to 5V a switching regulator might be more reasonable - any linear
    regulator is only going to be 41% efficient for that voltage range, switching regulators are
    typically 80 to 90% efficient.
    Thanks for your answer Mark!
    I was calculating like this, maybe I made an error?

    (12V - 5V) * 0.05 A = 0.35 W
    Junction-to-ambient (via datasheet) = 200C/W
    Maximum junction temperature (via datasheet) = 125C
    So
    0.35W * 200C/W = 70C, which would leave 125C - 70C = 55C headroom.


    I am assuming a current draw of the Teensy 3.2 of ca. 50 mA. But as mentioned, I am unsure about that value, too.

  4. #4
    Senior Member
    Join Date
    Jul 2020
    Posts
    1,368
    0.35W * 200C/W + 25C = 95C. Temperature rise above ambient. Ideally keep components below 50C for a long reliable life and
    avoid burning yourself too(!)
    If you start pulling current from the Teensy pins the current will increase too, so you might get to the point the regulator
    shuts down to protect itself. Personally I'd consider buck conversion down to 5V, or to 6V followed by a low-dropout
    linear regulator if sensitive circuitry is likely to be involved. But a single linear regulator is nice and simple, and reliable if
    not pushed too hard.

  5. #5
    Thanks again, Mark!
    It makes sense. It seems I need another solution.
    In your earlier post you mentioned a switching regulator. Could you point me in the right direction for the correct component?

  6. #6
    Junior Member
    Join Date
    May 2021
    Location
    Canada
    Posts
    9
    Quote Originally Posted by uleria View Post
    Thanks again, Mark!
    It makes sense. It seems I need another solution.
    In your earlier post you mentioned a switching regulator. Could you point me in the right direction for the correct component?
    If you can allow the extra footprint space (TO-220/SIP-3), there are several off-the-shelf DC-DC "7805 replacement" converters from CUI, RECOM, Traco and several other vendors. Most of them will support at least 500mA with up to 90% efficiency, and you can always install them upright since they won't be needing a heatsink anyway.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •