120V AC to 12V DC power supply questions

Discussion in 'The Projects Forum' started by slisgrinder, May 13, 2009.

  1. slisgrinder

    Thread Starter Active Member

    Dec 7, 2008
    Hey guys,

    I am trying to come up with a way of getting 120V AC to 12V DC and here is what I came up with:

    I would need a step down transformer which has 1 winding for every 10 windings according to my physics formula from a year ago. Then the 12V AC would have to go through a full wave bridge rectifier from AC to DC and add a capacitor between the "+" and "GND" leads of the DC output. Also assuming that I did the calculations correct, if I step down 120V to 12V my amperes should be (assuming household amperes at 20A) 200A ?!?!?. Is that correct? And do I need to worry about it?

    This power supply is being used to power a Microcontroller which takes in 12V DC (I am using a 7805 voltage regulator to step it down to a usable 5V) which controls high power LEDs which live off the 12V DC that was just created.

    So am I correct or is there another way to do this?
  2. bertus


    Apr 5, 2008

    Theoraticaly you are correct, practicaly not.
    A transformer has more turns per volt around the body.
    Here is a page from the EDUCYPEDIA with several links on transformaers.

    Here is also a page with several links to powersupply schematics:

    One of the links on this page leads to this page from Boll Bowden:

    PackratKing and cpqfe29 like this.
  3. slisgrinder

    Thread Starter Active Member

    Dec 7, 2008
    Thanks for the links, after some more research, I guess what I am trying to go for is a regulated power supply as it remains a constant voltage while supplying as much current that is consumed and is able to output within its safe limits. Now onto making a schematic so that I can get some more help if needed. Thanks Bertus...