Buck Boost: no proper ground reference

Discussion in 'General Electronics Chat' started by anhnha, Jan 1, 2016.

  1. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Here are two buck boost converter topologies with no proper ground reference.
    Please explain what is the problem with it?
    http://i.imgur.com/7mosAbt.png

    [​IMG]
     
  2. crutschow

    Expert

    Mar 14, 2008
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    I see nothing wrong with it except a ground reference is not shown, but that has no effect on the circuit operation.
    I would not say it is "Improperly Referenced...", just that it has no ground reference.
     
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  3. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    I think it is meant to say that there is no common ground between input and output. When switch is ON both input and output shares the common ground. However, as switch is OFF no common ground exists.
    The author says that these topologies are unacceptable. That is what I am confused.
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    The only problem with this topologies is the lack of a command reference point between output and input.
     
  5. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Yes, I see. However, what is the problem caused by no common ground? How does it affect the circuit operation?
     
  6. Jony130

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    This circuit will work only if you have a floating input source. So, now instead of 3-terminal circuit, you have 4-terminal device.
     
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  7. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Actually when analyzing the operation of these topologies I don't see any problem with them.
    Could you give an example where it doesn't work?
     
  8. Jony130

    AAC Fanatic!

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    But this circuit will work.
     
  9. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    So what is the problem caused by no common ground? I see that there is no common ground in these topologies but don't understand why it is source of problems.
     
  10. Jony130

    AAC Fanatic!

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    Now we have a 4-terminal device instead of the usual 3-terminal, input source cannot have any low impedance connection between Vin and Vout.
    Have you seen any single- supply circuit without common ground between Vin and Vout?
     
  11. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Could you explain about low impedance connection? What is it?
    I don't remember but maybe those above are the first ones.
     
  12. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    First, let's take a moment to savor the Buckeye's victory over Noter Doter...

    OK, back to you... The *potential* problem exists only within the context of the application. If the overall system requires that the regulator input and output reference potentials be identical, that's a problem. If no such requirement exists, then no problem exists either. There is no such thing as one grand universal power supply circuit/system/solution. Supplies always exist in the context of their source and load. To proclaim that one supply technique is good and another is bad without any context or qualifiers is anti-instructional, arbitrary and sloppy.

    And another thing - "proper" ground reference - ??? Let me counter that stupid proclamation with this: Whoever wrote that does not understand what a circuit ground is, "proper" or otherwise. Again, no context = no brains.

    ak
     
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