Current entering opamp via output pin! i'm not getting how its possible. help?

Question

in opamp clamping ckt, cap charges via a diode, current going into(wow! how?) opamp thru its o/p pin. where(how) does the path get completed for cap to charge to the input voltage?

if current enters opamp thru its o/p pin, where does it come out from?

hlp, its eatin my head!

Answer 1

Yes, the cap does charge thru the output pin of the op-amp.  Op-amps are capable of both sourcing and sinking current.  In this case, the current "comes out" from the Vee negative supply to the op-amp.

Answer 2

A link to a picture of the schematic would be a good start...

Answer 3

Operational amplifiers are an attempt to come as close as possible to an ideal amplifier. An ideal amplifier would ahve the following characteristics:

  1.  Infinite voltage gain

   2. Infinite input impedance

   3. Zero output impedance

   4. Infinite bandwidth

   5. Zero input offset voltage (i.e., exactly zero out if zero in).

In real life, they depart from this ideal:

    * The input current isn't exactly zero.

    * The input offset current isn't exactly zero either.

    * The input impedance isn't infinite.

    * There is a limited common mode voltage range.

    * The output impedance isn't zero.

    * There are voltage gain limitations including phase shifts.

    * There is a finite input offset voltage.

    * There is a finite slew rate.

    * There is some temperature dependence.

Once you apply feedback (to control gain):

I. The output attempts to do whatever is necessary to make the voltage difference between the inputs zero.



II. The inputs draw no current.

Note I <......