abt op-amp

Discussion in 'General Electronics Chat' started by fari, Nov 14, 2005.

  1. fari

    Thread Starter New Member

    Nov 14, 2005
    i have a very basic question about op-amp.as we know that the input current is
    ideally zero due to infinite input impedence.then how all the circuitry works if input
    current is zero.
  2. pebe

    AAC Fanatic!

    Oct 11, 2004
    Those op-amps that have a very high input impedance use FETs. They are controlled by a voltage - not a current.

    Have a look at the tutorials on this site where op-amps and FETs are explained very well.

  3. hgmjr

    Retired Moderator

    Jan 28, 2005
    Your thought process is sound. "Zero current" is certainly a condition that would appear to be somewhat non-productive.

    It is a good idea for you to carefully review the material you will find at the link that Pebe has directed you to. There you will discover that "zero input current" and "infinite impedance" are assumptions made for the purpose of simplifying the calculations associated with opamps such as gain and frequency response.

    Modern opamp technology including the fet-input opamps to which pebe referred has progressed significantly from the early days. The new devices come very close to achieving these two conditions. For that reason, the new opamps behave more predicably than the earlier generation devices.

    If you plan to do any analog design you will do well to become familiar with opamps for they play an important role in analog circuits of all types.