Transformer circuitary for low power devices

Discussion in 'The Projects Forum' started by abhichotu_abhi, Apr 1, 2010.

  1. abhichotu_abhi

    Thread Starter New Member

    Dec 3, 2009
    I am in the process of designing a circuit that will use a Step-down transformer to convert 220V AC to 110V AC.
    This circuit will power an adapter whose ratings are as follows:
    120V AC, 60Hz, and 2W.

    Now, I want to know that What should be the values os R(primary) and R(secondary), so that i am able to achieve the required output.

    Also, i will be adding a circuit breaker at the ouput Transformer for safety purpose. Should i use it at the input side too???

    Also, What should be used for properly insulating the X-mer from the iron sidewalls of the cabinet in which i will be fitting it.
    Any suggestions on improving the design is welcome.:)
  2. abhichotu_abhi

    Thread Starter New Member

    Dec 3, 2009
    Common friends, I need help!!
  3. ifixit

    Well-Known Member

    Nov 20, 2008
    I'm not sure what you want:confused:. Are you building a transformer? It would be easier and safer to buy one. If you don't need isolation, an auto-transformer would do.

    In case your building...

    • 2 Watts is very low power. No circuit breaker required, maybe a quarter amp fuse would do on the primary side only.
    • Secondary current is only 110/2W=18mA, primary will be approximately 9 to 10 mA.
    • You can use a small gage wire, but keep the primary DC resistance less than 800Ω, and the secondary less than 400Ω.
    • Use a EI core size suitable for 50VA. This is alot more than needed for the power, but proper termination and insulation take up space.
    Good Luck,