5V Isolated Supply

Discussion in 'The Projects Forum' started by blah2222, Nov 20, 2013.

  1. blah2222

    Thread Starter Distinguished Member

    May 3, 2010
    Hi all,

    Working on a project that detects EMG data from the forearm and ultimately it will be battery powered. For the meantime I don't really want to run through a wack of batteries as it is quite costly.

    Safety is the utmost concern as I will be connecting this to my arm. The commercial isolation transformers online seem to be pretty pricey, wondering if there is a more economical approach to design a system that I can use for prototyping.

    It will need to be a 5V supply for some low power op amps/instrumentation amp.

  2. wayneh


    Sep 9, 2010
    The current draw of these is normally very low, so a battery seems like a very viable option. A 4-pack of AAs could likely be used directly without any regulation circuitry.
  3. #12


    Nov 30, 2010
    This doesn't seem like a problem to me. Try a wall wart. Most of us have a box full. Don't you? If not, go to the local flea market and buy a box full of orphaned wall warts for $1 each.
  4. JohnInTX


    Jun 26, 2012
    Check out DC-DC converters, too. This page from Mouser has bunches of them. There is a standard for medical isolation. Offhand, I can't remember what it is but you might want to investigate that as well.

    Have fun.
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    Strictly speaking, what you need is a medical approved power supply. But well as long as you do not connect this equipment to any real patients. Just use any 5 volt power supply. You are working far away from heart. So the hazard real low in your case
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Just get some rechargeable batteries and swap them as needed. You can get four packs of AA NI-MH really cheap at Fry's. They are good for about 2500 mA-hr.
  7. blah2222

    Thread Starter Distinguished Member

    May 3, 2010
    Thank you for the recommendations all.

    Think I might just go with the wall-wart.

  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    You can do your own evaluation of the safety isolation of a wall wart power supply. There is an AAMI standard for testing that includes the test device, techniques, and safety standards: http://courses.engr.illinois.edu/ece445/documents/Safe_Current_Limits.pdf
    The leakage load I've used is in the attached schematic. All you will need to do is attach one lead to an earth ground, and touch the other to your power supply's output leads, one at a time (while it's plugged into the wall). For you patient-connected device, you want a measured reading of less that 50mVAC (50uA).

    Last edited: Nov 21, 2013