## Equivalent Circuit of Practical Op Amp

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 A_{OL}, Vd is the Thevenin’s equivalent voltage source while R_{0} 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.