Op-amps how could this possibly be a comparator?

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Discussion Overview

The discussion revolves around the classification of operational amplifiers (op-amps) as comparators or inverters, specifically examining two op-amp configurations. Participants explore the definitions and characteristics of feedback in relation to these configurations, as well as the behavior of an LED connected to the output of a comparator.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asserts that the first op-amp has a feedback loop and therefore cannot be a comparator, while the second is clearly a comparator.
  • Another participant challenges this view, stating that there is no negative feedback present in the first op-amp, suggesting that it can still function as a comparator.
  • A follow-up comment clarifies that feedback requires output to feed back to the input, specifically to the negative input for negative feedback.
  • There is a discussion about the connection of R1 and whether it constitutes feedback, with some participants providing definitions of feedback.
  • One participant inquires about the behavior of an LED connected to the output of a comparator, questioning if it will light up only when V+ is greater than V-.
  • A response indicates that the LED's behavior depends on its connection, explaining how the output state affects the LED based on its configuration.

Areas of Agreement / Disagreement

Participants express differing views on whether the first op-amp can be classified as a comparator due to the presence of feedback. The discussion remains unresolved regarding the classification of the first op-amp, with multiple competing interpretations of feedback and comparator functionality.

Contextual Notes

Some participants reference specific configurations and assumptions about feedback that may not be universally agreed upon. The definitions of feedback and comparator behavior are not settled, leading to varying interpretations of the op-amp configurations discussed.

Femme_physics
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I'm asked which type of op-amps these are

http://imageshack.us/photo/my-images/707/opamps.jpg/I think it's clear the SECOND one is a comparator, but the FIRST one is an inverter IMO. It has a feedback loop. If it has a feedback loop, it can't possibly be a comparator! Am I right or what?

The solution manual my teacher made, had them both written as "comparators" :confused:
 
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Femme_physics said:
I think it's clear the SECOND one is a comparator, but the FIRST one is an inverter IMO. It has a feedback loop. If it has a feedback loop, it can't possibly be a comparator! Am I right
No, sorry, you're wrong. :frown:

Look closer, there is no negative feedback, no feedback of any description, in fact.

There are inverting comparators, and there are non-inverting comparators.
 
where R1 is connected- that's not feedback?
 
Femme_physics said:
where R1 is connected- that's not feedback?
R1 just goes to earth. Feedback requires some of the output to feed back to the input (to the (-) input for negative feedback).

(If you ever see positive feedback (i.e., back to the + input) then that makes a comparator.)
 
R1 just goes to earth. Feedback requires some of the output to feed back to the input (to the (-) input for negative feedback).

Duly noted, thanks for this explanation :-)
 
I assume that whenver there is a LED after the comparator, only if V+ > V- , then the LED will light up. Is that a correct assumption to make? Also in my specific case?
 
Femme_physics said:
I assume that whenver there is a LED after the comparator, only if V+ > V- , then the LED will light up. Is that a correct assumption to make? Also in my specific case?
The output that lights the LED is dependent on where the LED's other pin is connected. :smile:
If the LED is connected between output and ground then it will light up when the output goes high.

In your case, the LED is connected between OP-AMP output and +Vcc, meaning that when the output is high, there will be not much voltage across the LED.

So ...
 
That clears it :) Thank you
 

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