subharpe
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Since very little current flows in or out of the input terminals of the op amp,
we saw that there was essentially no voltage drop across RB which caused the (+)
input terminal to remain at ground potential. Since % is always near 0 as long as
the amplifier remains unsaturated, this means that the (-) input terminal must
also remain very near to ground potential. This is an important concept. Although
the (-) input is not actually grounded, it remains very near ground potential. We
commonly refer to this point in the circuit as virtual ground.
subharpe said:Thank you, but not really helped. I did not ask about the term virtual. I wanted to ask about the term ground. It needs not be grounded always. Isn't it?
Kral said:subharpe,
If you consider the virtual ground as being an AC (dynamic) ground the term makes more sense in that the voltage on the inverting input is independent of the current flowing into the node, since the feedback causes an equal and opposite current to flow out of the node.
Regards,
Kral
a very very small current 0.75µA will flow between the terminals
biff44 said:............
And it is just a rule of thumb. There are plenty of conditions, especially transient ones, where the rule is not true.
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