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explanation required(virtual ground)

Discussion in 'General Electronics Chat' started by konzen, Aug 30, 2007.

  1. konzen

    konzen New Member

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    hi,

    recently in uni i've been dealing alot with op-amps and most of the circuits i am required to build have virtual grounds. while knowing how to create a virtual ground, i do not really understand the concept of a virtual ground. all i know is that it is a point in the circuit where the voltage is held constant and is the substitute of a real ground. my lecturer's explanation is confusing and wikipedia's article is too deep. can u guys help out? i want to know how a virtual ground really works and when do we need one. thx in advance
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Depends really what you're actually talking about?.

    Opamps generally need a split supply (it gives many advantages), and if you only have a single supply you can 'fake' a split supply with two same value resistors across the supply (a potential divider), with a decouling capacitor. This is sometimes known as a 'virtual earth'.

    Or for an opamp adder, this is called in audio circles a 'virtual earth mixer', because the mixng point at the inverting input has no signal on it, so is considered to be 'virtually at earth potential'.
  3. Optikon

    Optikon New Member

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    A virtual ground is a result of an opamp trying to keep its two input terminals at the same potential when used in a feedback circuit.

    Take a look at a standard inverting opamp amplifier configuration.
    We know that (ideally) current does not flow into an opamp input terminal.
    So when the (+) terminal is held at say ground (or some other DC), the opamp will do what it needs to to also make its (-) input at the same potential. If this potential happens to be ground (common in many cases) then input current will flow towards that "ground" potential but not go into the opamp input terminals since they do not sink current. So a ground potential which actually cannot sink current is called a "virtual" ground.
  4. konzen

    konzen New Member

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    i think i'm starting to get a rough idea. so virtual grounds are only truly required when working with op-amps? and also my project this semester involves rotating a dc motor cw and ccw quickly. been reading up on H-bridges but do you guys have any online links where i can refer to? the budget im given does not allow for a motor driver. thanks alot!
  5. mike11298

    mike11298 New Member

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    Virtual ground is usefull for other circuits, too. Not just op-amps. Search google for H-bridge? or have a look here Motor control This came from this forum just a few questions away.
    Last edited: Aug 30, 2007
  6. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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