Connect with us

Linear Power Supply Help!!!!

Discussion in 'Power Electronics' started by ChanceAcidRapper, Apr 7, 2016.

Scroll to continue with content
  1. ChanceAcidRapper

    ChanceAcidRapper

    4
    0
    Apr 7, 2016
    Hello all,

    I am currently in the midst of building a power supply for a school project, but I am stumped. The requirements- +12v -12v +5v +Var and -Var (7812, 7912, 7805, 317, and 337). Now when it comes to setting up each individual regulator, I got it; however, I cannot for the life of me figure out how to run all lines together on one PCB. I am slightly confused on what I can run off the main lines of the bridge rectifier to each individual regulator, on what lines I can share capacitors to lower parts count but maintain minimal noise, and so on and so forth. If anyone can shoot me some pointers it would be much appreciated! As I stated, I understand how to run each individual regulator (or pairs,) but cannot figure out how to run all 5 together on the same board!

    Thanks you for any and all help!
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,355
    2,255
    Nov 17, 2011
    The essence of your project is:
    A power source (transformer, rectifier) with at least 1 positive and 1 negative raw output voltage. 5 separate regulators (3 pos, 2 neg.). They all need to share a common ground (0V).

    The detailed setup depends mainly on the power source:
    • which output voltages and configurations are available from the transformer (e.g. do you have separate windings for the 5V output or are you going to take the 5V from the 12V rail)?
    • what current requirements do you have for the several outputs?
     
  3. ChanceAcidRapper

    ChanceAcidRapper

    4
    0
    Apr 7, 2016
    Thank you for the quick reply! Yes, a 115V transformer with a bridge rectifier with a positive and negative feed. They do need to share a ground. I do not have current requirements for the project. The test goes for unloaded and loaded for each output (both 12s, both Var, and the 5) along with ripple in mV (unaware of what the test load will be). I am still completely stumped.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,355
    2,255
    Nov 17, 2011
    This is how you do it:
    upload_2016-4-7_8-32-42.png

    The variable regulator(s) are set up the same way.

    Note that the 5V regulators will dissipate a lot of power as the voltage drop across the 7805/7905 is ~10V (power ~ 10V*Iout)!
     
    Arouse1973 and davenn like this.
  5. ChanceAcidRapper

    ChanceAcidRapper

    4
    0
    Apr 7, 2016
    So essentially, I can tap off of the +15 for my +5, and since I do not need the 7905, I can come off of my rectifier lines with my 317 and 337 as well?
     
  6. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    You can as Harald showed you but the 7805 will disipate a lot of heat.
    You should use the 317 and 337 in the same way as the others,
    it has nothing to do with the use of the 7905.
     
  7. ChanceAcidRapper

    ChanceAcidRapper

    4
    0
    Apr 7, 2016
    As in, use the 317 and 337 as the 7812 and 7912 is used? Off of the bridge rectifier?
     
  8. dorke

    dorke

    2,342
    665
    Jun 20, 2015
    Yes,
    more accurately put: off the unregulated voltages.
     
  9. Herschel Peeler

    Herschel Peeler

    401
    65
    Feb 21, 2016
    How much current do you need? The transformer and rectifier must be able to deliver these needs. LM317 and 337 can be added to the previous schematic easily.
    Fused? Circuit breaker? Electronic fuse? Something is suggested especially for a classroom.
    A single supply that does it all or various smaller supplies? The problem with one big one is if it dies all exercises are off. A lot of small cheap ones might be better.
    What do the exercises actually call for? Low voltages at a fraction of an amp? "Wall warts" are pretty cheap.
    For my use I have collected a bunch of adapters. I add a voltage regulator with current limiting.
    Designs available if you are interested in this approach.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-