# How to Stabilize the Output Voltage Using a OP AMP Comparator Circuit and Draw Current(1A) from it?

#### sghioto

Joined Dec 31, 2017
5,427
We seem to be going in circles.
OK. What is the purpose of the 741? How is it being used in this particular circuit?
SG

#### crutschow

Joined Mar 14, 2008
34,835
OK. What is the purpose of the 741? How is it being used in this particular circuit?
Pin 2 is the 741 summing junction, with linear negative feedback from -Vo to this junction.
It adjusts -Vo so that the pin 2 voltage is equal to the pin 3 (+) voltage (0V / ground), which means -Vo always equals (+)Vo (the tracking function).

The 741 may be "comparing" two voltages, but it's doing it in a linear feedback mode, not as an open-loop, digital-out comparator.

#### sghioto

Joined Dec 31, 2017
5,427
The 741 may be "comparing" two voltages, but it's doing it in a linear feedback mode, not as an open-loop, digital-out comparator.
Exactly. So a comparator with an analog output?
SG

#### crutschow

Joined Mar 14, 2008
34,835
Exactly. So a comparator with an analog output?
SG
No. Read what I said again.
The usual definition of an analog "comparator" circuit is a high gain amp with a differential input, operating open-loop (or possibly with a small positive feedback to give some hysteresis to the trip point) and giving a digital (2-state) output.
If the amp is operated with closed-loop negative feedback to give an analog output, it is operating as an op amp, not a comparator.

Comparators, by definition, do not have an analog output.

#### sghioto

Joined Dec 31, 2017
5,427
If the amp is operated with closed-loop negative feedback to give an analog output, it is operating as an op amp, not a comparator
Understood. My intent was never to imply the circuit had a digital output but was referring in general terms as you stated.
The 741 may be "comparing" two voltages,
SG

#### DickCappels

Joined Aug 21, 2008
10,246
Maybe this will help, referring to the schematic in post #22, the circuit with the opamp is applying feedback based on how close to ground (pin 1, - input) the inverting input (pint 2, - input) is. The amplified difference is used to force the negative output voltage to a voltage tcauses the voltage on pin 2 to be as close as possible as ground. Essentially, comparators only have two states. Opamps have continuously varying outputs.

#### crutschow

Joined Mar 14, 2008
34,835
My intent was never to imply the circuit had a digital output but was referring in general terms as you stated.
Okay.
The point is that the word "comparator" in never used to refer to an opamp linear output circuit, even in "general terms".