GROUND for two different voltages

Discussion in 'The Projects Forum' started by KansaiRobot, Feb 16, 2010.

  1. KansaiRobot

    Thread Starter Active Member

    Jan 15, 2010
    318
    5
    Hello

    I have always been told that if we are using a circuit with two different voltages (say 5V and 12V) we should as much as possible separate the grounds.

    What happens if instead of two power sources we use only one (say 12V) and some circuit involving a regulator to generate the other (5V) (something like a DC-DC)

    say:

    Code ( (Unknown Language)):
    1.  
    2.  
    3.  
    4. 12V--------------------------[78L05]-----------------------5V
    5.             |      |             |          |             |
    6.            ==      ==            |          ==          == (capacitors)
    7.             |      |             |          |             |
    8. GND---------------------------------------------------------------
    9.  
    10.  
    Is it ok now to use just ONE GROUND connection for both 5V and 12V circuits???

    Thanks in Advance

    Kansai
     
  2. 7Arrows

    New Member

    Feb 14, 2010
    11
    0
    I don’t know if it’s ok for what you’re doing but it’s done all the time duel voltage systems like this one.
    7Arrows
     
  3. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Grounds of separate power systems are often kept separated for a whole lot of other reasons but most are connected together in a lot of designs.

    One cannot simply use a generalization to cover all situations.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,685
    900
    It is OK to use one ground with the voltage regulator circuit as you have shown. In fact, I don't think it will work if the 12V source and regulator are referenced to separate grounds.

    John
     
  5. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Also remember that a schematic often is a simplified drawing. Then it comes to building the hardware the connections in the schematic do not have to replicated 100% as drawn in the schematic. If you build your voltage regulator on breadboard or PCB you will probably select a star ground topology
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    If you are using a mixing high power devices and logic, it is a good idea to run the respective grounds separate from each other to the respective devices, i.e. one ground to the high power circuits and another to the logic devices. Both would be tied together at the actual power supply. Reasoning for this it to keep the high power devices from imparting unwanted voltages into the ground line of the logic devices.
     
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