Power supply question

Discussion in 'The Projects Forum' started by Talguy, Sep 1, 2009.

  1. Talguy

    Thread Starter Member

    Aug 17, 2009
    I'm working on building a power supply for my first project. My question is I need three voltage outputs 3.3, 5 and 12 volts to power my pic and peripherials, so long story short can I use a voltage regulator to get 12v and voltage dividers off the 12v to get the two other outputs

  2. SgtWookie


    Jul 17, 2007
    Short answer is: no.
    You'll get very poor regulation for 5v and 3.3v.
    Consider converting an ATX form factor computer PS; it already has those voltages available with plenty of current.
    MPJA has them for under $10: http://www.mpja.com/prodinfo.asp?number=17986+PS
    Google "ATX bench supply" for conversion ideas.
  3. Electronworks

    New Member

    Sep 1, 2009
    This might help you:

    It depends on the current of each rail, but I would use a 7812 for the 12V rail and a 7805 for the 5V and any old 3V reg for the 3.3V.

    Make sure your heat is less than 0.5W to keep everything from cooking. heat can be worked out from: (Input voltage - output voltage) x load current

    Bill Naylor Electronic kits for Education and Fun
    Last edited by a moderator: Sep 1, 2009
  4. jj_alukkas

    Distinguished Member

    Jan 8, 2009
    If you need light output per source like below 100mA, you can use a voltage divider with zenners from a 12v, but that is not feasible with minimum efficiency and hot divider resistors.

    Better and standard way would be to use 7805 and 7812 and get the 3.3 with a voltage divider with zenner. If current is below 100mA, you can even use the 'L' series in a small TO-92 plastic case.