Multiple_Floating_DC_Power_Supplies

Discussion in 'General Electronics Chat' started by odm4286, Mar 23, 2014.

  1. odm4286

    Thread Starter Active Member

    Sep 20, 2009
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    Hey everyone, I'm learning so bare with me while I try to put my question into words.

    Is there anything wrong with tying all the negatives of multiple dc power supplies together? So lets say I had a three separate floating(non earth referenced) power supplies, 3vdc, 12vdc, and 24vdc all powering different components in a circuit.

    Would it be safe to make all the negatives of these power supplies common to each other?
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    I do it all the time.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,548
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    +1, In the systems I build I usually reference them to earth ground, however.
    Max.
     
  4. odm4286

    Thread Starter Active Member

    Sep 20, 2009
    155
    5
    Ok thanks guys just to be safe heres an example. Ps1 24vdc to resistive load, resistive load to Collector of npn transistor, ps2 3vdc to base of transistor, emitter to ground, negative of both supplies to ground
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    This sounds like a common open collector arrangement, such as used common level transition method.
    Max.
     
  6. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    It won't work if you don't connect the grounds together.
     
  7. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    ps2 3vdc to base of transistor, it should be in series with a Rb resistor, did you do that?
     
  8. odm4286

    Thread Starter Active Member

    Sep 20, 2009
    155
    5
    That's exactly why i ask. The first time i played with transistors i had that problem so i ended up just using one 24vdc supply and regulators all over the place.

    Good to know i can tie negatives together of different dc supplies to accomplish the same thing.

    Yes sorry i forgot about the current limiting resistor to the base. That was just something i typed quick to get my idea across