Need some advice for my PSU project.

Discussion in 'The Projects Forum' started by FrancescoC, May 10, 2015.

  1. FrancescoC

    Thread Starter Member

    Nov 22, 2014
    i am designing a PSU to use for my projects.
    When it is finished should be able to supply 0V-25V dc and 0A to 3A.

    My design consists of a mains transformer, abridge rectifier, a tracking preregulator and a final regulator.
    There will be current limiting facility and the current and voltage are controlled by a PIC microcontroller.

    I am uploading a file for the analogue section of the design and would be nice if you could look at it and make any comment you think is appropriate.


  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    its over the top, too much stuff, and i cant see it working,plenty of simple designs using Lm317 regulator and transistor assistance current regulator on the internet.
  3. FrancescoC

    Thread Starter Member

    Nov 22, 2014
    Hi Dodgydave,
    Can you please explain why do you think it will not work?
    I have simulated the circuit with LTSPICE and seem to perform as expected!


  4. crutschow


    Mar 14, 2008
    It may work but it seems overly complicated for your needs.
    What type of preregulator do you want to use, linear or switching?
  5. doozer

    New Member

    May 11, 2015
    Depends what you need it for but it's probably cheaper to buy a second-hand TTi PL series supply which has the same feature-set than build that. Also, watch out for strong part dependencies on Linear Tech components - make test gear parts fungible if you can. I haven't reviewed the design however - just had a glance so I can't comment on the engineering.
  6. FrancescoC

    Thread Starter Member

    Nov 22, 2014
    Hi guys,
    Thank you for your replay.
    Yes I could buy one...but. It is much more fun to make one by yourself.

    It may looks overcomplicated, but in order to achieve the result i want it is necessary to have some complication.
    Please read this brief explanation why I am doing it this way. If you see a better way to get the same result I would be very grateful.

    So you have the usual bridge rectifier and smoothing capacitor(s).
    Then I have a charging resistor (to reduce the inrush current) and a bypass relay.
    Then there is a second relay to turn ON/OFF the output.
    Then there is an LM317 with bypass transistors to give me a 'stress-free' 3 Amp output. The LM317 act as a preregulator that is 3V above the final regulators.

    The idea is to get a good regulation and low power dissipation from the output regulators. With a low differential IN/OUT voltage they will deliver the max current and keep cool
    The voltage and current are set by Op-amps connnected to them.
    The Op amps are controlled by a PIC Microcontroller, using a pair of DACs.
    There is also current sensing circuitry between the preregulator and the final regulators.

    As it stands the circuit should be able to deliver 0V-25V at 2.5A.

    Please comment and ask any questions.