Question

What is open loop Vs close loop

In a Omp amp

What’s the difference or its terminology(usage)???

Answer 1

Note- See Diagrams at the end

Open Loop Case

1. In open loop, Opamp is used without feedback.

2. It acts as a Voltage comparator (i.e. Comparing with )

Closed Loop Case

1. In closed loop, Opamp is used with feedback - either positive feedback or negative feedback

a) Positive feedback

In positive feedback, Opamp has many applications like Schmitt Trigger, Waveform generators (square, triangular etc.) etc.

b) Negative feedback

In negative feedback, Opamp can be configured as various types of Amplifiers (Inverting, Non inverting), it can perform mathematical operations like addition, subtraction, log, antilog, multiplier etc. By using Opamp in negative feedack circuit we can also make filters.

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1. When opamp is used without feedback and with positive feedback, the opamp remains in saturation region.

2. When opamp is used with negative feedback, the opamp remains in linear region

where is the voltage at output when opamp is in saturation region

   is the output voltage

   is the difference voltage at the input terminals of opamp (i.e. )

is the open loop gain of opamp (gain without feedback)

3. In negative feedback opamp circuits, Inverting and non-inverting nodes are said to be virtually short circuited because there voltages become equal (i.e ) without any physical short circuit between them.

4. If opamp is used with positive feedback, difference voltage becomes large enough, therefore opamp will be in saturation i.e.