Equivalent Circuit of Practical Op Amp – The circuit which represents op-amp parameters in terms of physical components, for the analysis purpose is called equivalent circuit of an op-amp. The equivalent circuit of an op-amp is shown in the Fig. (A)
The circuit shows the op-amp parameters like input resistance, output resistance, the open loop voltage gain in terms of circuit components like Rin R0 etc. The op-amp amplifies the difference between the two input
The output voltage is directly proportional to the difference voltage Vd.
It is to be noted that the op-amp amplifies difference voltage and not the individual input voltages. Thus the output polarity gets decided by the polarity of the difference voltage Vd .
The voltage source AOL, Vd is the Thevenin’s equivalent voltage source while R0 is the Thevenin s equivalent resistance looking back into the output terminals.
The equivalent circuit plays an important role in analysing various op-amp applications as well as in studying the effects of feedback on the performance of op-amp.