Open Loop Configuration of Op amp:
Open Loop Configuration of Op amp – The simplest possible way to use an op-amp is in the open loop mode. The Fig. 2.13 shows an op amp in the open loop condition.
We know that the d.c. supply voltages applied to the op-amp are Vcc and -V ;E and the output varies linearily only between Vcc and -Vee
Since gain is very large in open loop condition, the output voltage V, is either at its positive saturation voltage ( + Kat ) or negative saturation voltage ( – Vs,„ ) as V] > V2 or V2 > Vi respectively. This is shown in the Fig. 2.14.
Thus very small noise voltage present at the input also gets amplified due to its high open loop gain and op-amp gets saturated.
It can be seen from the Fig. 2.14, only for small range of input signal (from point a to b), it behaves linearly. This range is very small and practically due to high open loop gain, op-amp either shows + Vsat or – Vsat level.
This indicates the inability of op-amp to work as a linear small signal amplifier in the open loop mode.
Hence, the op-amp is generally not used in the open loop configuration.
Such an open loop behavior of the op-amp finds some rare applications like voltage comparator, zero crossing detector etc.