Op-amps how could this possibly be a comparator?

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In summary, The first op-amp is an inverter with a feedback loop, which means it cannot be a comparator. The second op-amp is a non-inverting comparator. The presence of a LED does not determine the type of op-amp, but rather the connection of the LED determines when it will light up. In this specific case, the LED is connected between the output and the positive power supply, causing it to light up when the output is high.
  • #1
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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  • #2
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.
 
  • #3
where R1 is connected- that's not feedback?
 
  • #4
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.)
 
  • #5
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 :-)
 
  • #6
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?
 
  • #7
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 ...
 
  • #8
That clears it :) Thank you
 

1. How does an op-amp function as a comparator?

An op-amp can function as a comparator by amplifying the voltage difference between its two input terminals and outputting a high or low voltage depending on which input is larger. When the voltage at the inverting input is higher than the non-inverting input, the output will be low, and when the non-inverting input is higher, the output will be high.

2. What are the advantages of using an op-amp as a comparator?

Using an op-amp as a comparator offers several advantages, including high gain, fast response time, and low input bias currents. Additionally, op-amps are readily available and inexpensive, making them a practical choice for many applications.

3. Can any op-amp be used as a comparator?

While any op-amp can technically be used as a comparator, some may be better suited for this function than others. Op-amps designed specifically for use as comparators often have features like open-drain outputs and faster response times, making them more suitable for this application.

4. What are the limitations of using an op-amp as a comparator?

One limitation of using an op-amp as a comparator is its inability to handle large voltage differences between the input terminals. This can cause the output to saturate, leading to inaccurate results. Additionally, op-amps may not be able to handle high-frequency signals as well as dedicated comparators.

5. How can I ensure accurate results when using an op-amp as a comparator?

To ensure accurate results when using an op-amp as a comparator, it is important to consider factors such as input offset voltage, input offset current, and input bias currents. These parameters can affect the accuracy and stability of the comparator, so choosing an op-amp with low values for these parameters can help improve performance.

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