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problem with common ground

akhilesh sati
Intellectual 950 points

Other Parts Discussed in Thread: TLC071

i am using op-amp TLV071 and operating it with a battery of 3V. in order to see the output of the op-amp on the oscilloscope, the GND terminal of the oscilloscope is connected with the GND terminal of the 3v battery. My confusion is that, the GND is a reference voltage for any circuit and the GND of the oscilloscope is derived from 220V/50Hz,rms voltage.

1. so is it necessary that the GND of the oscilloscope and the GND of the Battery will be at the same potential.

2.In circuit many time we connect the GND of two different power sources for making their GND common & then measure all the voltages with respect to this GND. At that point of time how one ensures that all the power supplies have same GND voltage.

regards

akhilesh sati

  • 0
    Guru 21975 points

    Akhilesh,

    It certainly common to connect the ground of the battery to the oscilloscope ground. But this is not necessary. There might be some other circuit node at which you could connect the oscilloscope. It should, however, be a low impedance node. Connecting the oscilloscope ground to any node will generally add significant capacitance at this node to earth ground. Thus a high impedance node might be loaded with undesirable capacitance.

    I assume that you must mean that you are using TLC071 as TLV071 is not a valid part number.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Intellectual 950 points

    thanks sir for your response.

    but what will happen if two nodes (which are individually at different potential) will be connected for making a common ground.

    In practice the physical ground is earth, whch is having almost zero potential and rest of the grounds are of our choice e.g. while designing 5V dual power supply using two batteries,  the 5V is considered as ground. so in circuit designing how do we distinguish between different grounds.

  • 0 in reply to akhilesh sati
    Guru 21975 points

    Akhilesh,

    Sorry, but I'm not sure I understand your dilemma or question. If two node are connected, they assume the same potential. A node can be defined as ground (or common) in a circuit, yet be a different potential than earth ground. Connecting an oscilloscope ground lead to this same node will likely pull this node to earth ground potential.

    Regards, Bruce.

  • 0 in reply to Bruce Trump
    Intellectual 950 points

    Sir in the circuit that I have made above if i will connect one gnd to another gnd than i will end up with a lot of current flowing from one GND to another GND. because one GND is at 5v above than the another GND. then how to take care of such GND in circuits while interfacing two different modules supplied by two different power supplies

    regards

    akhilesh

  • 0 in reply to akhilesh sati
    Guru 21975 points

    Akhilesh,

    I don't see any problem in connecting these two ground unless the power supplies are interconnected in a way that you have not explained. The two grounds will assume the same potential when they are connected.

    Regards, Bruce