Converting 120VAC to 9VDC

Discussion in 'The Projects Forum' started by badfishadi, Aug 3, 2009.

  1. badfishadi

    Thread Starter New Member

    Aug 3, 2009
    Hello everyone! I am fairly new to working with electronics so please be gentle if my ideas are completely wrong. I am trying to build something that has several 120VAC components and a few components that I wish to power with 9VDC. One of these is a device that is supposed to run off of a 9V battery (which I would like to replace with wall power) and then a few LEDs and other basic components I need to lower the voltage for. I have been trying to come up with a way to provide a fairly reliable 9V regardless of load.

    These are the options I've been considering (keep in mind that I'd like to keep costs as low as possible):

    1) Use an unregulated transformer that outputs 12V ( and then reduce and stabilize (not sure if these are the right terms) the load using something like this:, but replacing the 7805 with a 7809 (are there any other modifications I need to make?). Cost seems to come out to a little over $15.

    2) Use a switching converter such as However I've been reaching a dead end trying to understand how to wire this, the diagrams in the datasheet are very confusing to a beginner. This unit costs around $15 and I'm not sure of the additional cost I would incur for the other parts necessary.

    3) Purchase a switching power supply: This is the most costly option at $25, but it seems to be premade and the easiest for me to use. Do I need any additional components to make sure that the voltage stays regular? The datasheet says "Use a 0.1uF ceramic cap. and a 10uF Electrolytic cap. on the output to measure Ripple & Noise at 20MHz BW". Is this necessary to reduce ripple & noise, or merely to measure it?

    Sorry if anything I've asked seems really ignorant, I've been searching the web to find something to read that would clarify my questions, but all google seems to give me is different vendors and overly technical (for me) explanations such as the ones in the datasheets. I'd appreciate any help you could give me to point me in the right direction. Thanks!
    Last edited: Aug 3, 2009
  2. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
  3. badfishadi

    Thread Starter New Member

    Aug 3, 2009
    Thanks for the suggestion, but I need 120V to come in from the wall for the other components that require it. So I'd ideally need something exactly like that made for internal use (which I'm hoping is what the 3rd option I listed was, I can't tell if it requires any additional components). I suppose I could take it apart and mount it inside the case, but I was hoping for something already made for internal use, although the pricepoint is appealing.
  4. Arm_n_Legs

    Active Member

    Mar 7, 2007
  5. badfishadi

    Thread Starter New Member

    Aug 3, 2009
    Thank you so much for all of your suggestions. The rohm module you posted is very similar to my option 2 isn't it? I'm afraid I'm lost when it comes to connecting it to my circuit in a safe way. Could you explain it? What I would ideally want is something ready-made like the wall smps blueroom posted, designed to be put inside a case (is this what my option 3 is? or does this need additional wiring?). Or maybe using option 1 with a transformer (does anyone have any feedback on this?) thanks!

    The article you posted seems promising, I'm going to read it and see if it makes any sense to me

    EDIT: Also, if someone could actually give me feedback on the options I've posted it would be great. If you are all suggesting something else, I guess they aren't great options, but I'd at least like to know why.
    Last edited: Aug 4, 2009