All Questions
Tagged with negative-feedback operational-amplifier
95 questions
25
votes
4
answers
3k
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Illustrating op amp feedback without control theory
We are teaching op amps in a high school class, before calculus. So we can't use control theory to teach how op amps respond. All the same, I would like to have an intuitive explanation for how a ...
- 1,691
11
votes
4
answers
3k
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What is the purpose of including (or excluding) the output resistor in the feedback loop of an op-amp buffer?
I have often seen (and made) circuits like this. It is a simple inverting op-amp buffer, plus a small current-limiting output resistor to protect the the op-amp if the output is shorted.
simulate ...
- 243
8
votes
3
answers
1k
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Operational Amplifier with mixed feedback
So, I came across this circuit in a test, it's regarding the operation of an op amp with multiple (positive and negative) feedback, the circuit is as follows:
I was asked to evaluate the following ...
- 83
7
votes
3
answers
4k
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Why is inverting op-amp behaving like a low pass filter?
can anyone explain why this circuit behaves like a low pass filter despite having no capacitor in the feedback loop?
- 109
7
votes
6
answers
887
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How is this op amp in negative feedback?
I'm trying to solve this question for homework but they mentioned the first op amp is in negative feedback. How though?
Is it because of the output of the second op amp (OA2) is also in negative ...
- 121
7
votes
5
answers
879
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Is transistor in cutoff?
In the following circuit, consider the op-amp to be ideal (gain = ∞ , input resistance = ∞) and transistor beta is 20 A/A
Initially I was using virtual ground concept here but in the given answer ...
- 71
6
votes
5
answers
2k
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Non-inverting op-amp
Why is resistor R1 connected to the inverting terminal of the op-amp in a non-inverting op-amp configuration? What will happen if we replace it with a short circuit?
- 117
6
votes
4
answers
5k
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What's the need for a small capacitor in the negative feedback parallel to a feedback resistor?
I have the following circuit:
I think I understand pretty much all the aspects of it except for the small capacitor in the feedback. What is the need for it? Judging by the frequency of 1 MHz that is ...
- 61
6
votes
3
answers
1k
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How does the op-amp stabilize?
I have a problem understanding one thing in op-amps, namely - when the cycle of stabilizing ends?
For example, when we have simple non-inverting amplifier, firstly the difference equals the amount of ...
- 63
6
votes
4
answers
606
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Using an op-amp in an unusual configuration with (inverted) negative feedback to the non-inverting input
Here is a question for those who understand unusual, non-conventional op-amp configurations.
Is there any reason an op-amp can't be configured with an input going to the inverting input, and the ...
- 63
5
votes
6
answers
3k
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How does opamp open-loop gain affect closed-loop gain in a circuit?
The gain of an opamp circuit is basically $$A_v=-\frac{R_f}{R_i}$$
But how come the gain of the opamp itself does not appear in the equation? How is the opamp amplifying anything in the circuit? What ...
- 61
5
votes
7
answers
1k
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Infinite output impedance in amplifier, instead of 0?
The question asks: "Exercise 14.5 Assume an ideal op amp and use the summing-point constraint to find an expression for the output current io in the circuit of Figure 14.14. Also find the input ...
- 111
5
votes
6
answers
1k
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In a negative feedback loop, why does increase in v_out lead to increase in v-?
I hope this is the right place to ask this question. (Please let me know if there's a better place to ask this.)
Basically, I'm quite confused about how we check if we have a negative feedback loop.
...
5
votes
4
answers
840
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OpAmp with common-mode voltages and zero feedback current
Circuit A is a classic non-inverting amplifier with a common-mode DC voltage 1 V to both its inverting and non-inverting input. Since 1 V has to appear at the inverting input, there is no voltage drop ...
- 1,448
4
votes
9
answers
855
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How is an inverting opamp adder circuit able to regulate its feedback?
Consider the typical opamp inverting adder as follows:
Why don't resistor Rl and R1 form a resistor divider and impose 2.5V upon inverting node and drive it to saturation. How is opamp's feedback ...
4
votes
5
answers
2k
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Unity Gain Amplifier Purpose
In layman terms, what is the main use and purpose of unity gain amplifiers? I am reading that it is used to "buffer high impedance sources" but I'm unsure what this means practically.
- 41
4
votes
4
answers
675
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How to prevent this op-amp from railing
I have the following circuit:
An input that can go negative (+/-5 V sine wave), and two inverting op-amps. The second op-amp is "current buffered" and is driving the base of a BJT.
Here is ...
- 549
4
votes
5
answers
5k
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Understanding Op-amp Negative Feedback
Have a look at the diagram above. It shows an op-amp with negative feedback. Ignoring the feedback loop for now, the voltage (pressure) coming from the 5V battery, acting on the inverting pin, ...
- 1,696
4
votes
3
answers
2k
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What happens to output if OPAMP its supply is tweaked?
Say the above OPAMP is normally operated with supply of +15V and -15V and output is said to swing from +15V to -15V. But I changed -15V power supply {of OPAMP} to -14V and Vi to:
(a)1V
(b)-15V
(...
- 93
4
votes
2
answers
387
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Parasitic oscillations for phase shift not equal to -180 degrees
From "Learning the Art of Electronics" by T. Hayes and P. Horowitz, Cambridge University Press (p. 360):
As per above figure, the LF411 op-amp imposes a -90 degree phase shift on output ...
- 115
4
votes
4
answers
1k
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Using an op-amp to drive LEDs according to an incoming signal
The following schematic was suggested for visualizing the frequency (which is variable) of an oscillator using two LEDs that light up alternatingly. It seems that the value of the resistor determines ...
- 721
3
votes
3
answers
623
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Why doesn't the following circuit have negative feedback?
Consider:
The Sedra book says that it's a Schmitt trigger, so there is positive feedback, but why doesn't it have negative feedback as well?
- 133
3
votes
2
answers
909
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Difference OTA and op-amp
I have a question about OTA (operational transconductance amplifier). Why can an OTA can be used without negative feedback but would still be able to keep its inputs (V+, V-) close each other? I have ...
- 341
3
votes
2
answers
226
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How are opamp node voltages being set in the following circuit and what is the use of the diode configuration?
I am using a PCB which has the following opamp configuration implemented. It's supposed to be a precision buffer for the source V3. I accidentally connected the source V4 as well and observed strange ...
3
votes
1
answer
145
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I don't understand this temperature controller circuit's behaviour [duplicate]
I am trying to build a circuit to regulate temperature for a few microheaters. Here's the circuit I am using:
This is a constant temperature controller circuit often found in the research papers and ...
- 31
3
votes
2
answers
153
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Operational Amplifier - Virtual ground
In the question above I was asked to solve the general shape of Vout, and the exact values in t=0.5ms,1ms.
My question is - can I approximate a constant virtual ground in the negative input of the ...
- 94
3
votes
3
answers
830
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Negative resistance circuit
The circuit is inputted with a 200Hz sine wave and the amplitude is varied. I believe the circuit is operating with negative feedback. But also the 8.2K resistor is then switched to an 18K resistor in ...
- 109
2
votes
5
answers
983
views
Sensor datasheet shows op-amp circuit with capacitor to ground from inverting input. How does this work?
In the circuit above the inverting input feeds to ground through a capacitor.
The output should be a constant voltage used for reading into an ADC/taking a measurement.
A negative feedback op-amp ...
- 367
2
votes
4
answers
297
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Learning the Art of Electronics 9N.4 -- low-dropout voltage regulator
I have trouble understanding one circuit in section 9N.4 of the book "Learning the art of electronics" by Thomas C. Hayes. I attached a screenshot of that section below.
I understand the ...
- 51
2
votes
3
answers
248
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Why can't the following configuration be considered negative feedback?
In the following circuit I have kept the resistor ratio such that beta factor of negative terminal (part of output will come on inverting terminal by voltage division), is higher than that of positive ...
2
votes
2
answers
602
views
Identifying a multiple feedback op-amp circuit
I stumbled upon the circuit above, and am trying to understand what its frequency response would be. I just started learning about filters, but haven't come upon a multiple-feedback topology like this....
- 61
2
votes
1
answer
763
views
Op-Amp output inconsistent with theory
I was just playing around with a few Op-Amp circuits, and suddenly got stuck on this simple one.
As the circuit shows, the Op-Amp output is connected to its non-inverting input terminal, so it should ...
- 186
2
votes
2
answers
5k
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Individual Phase shift provided by Op-Amp in Closed loop configuration
When comparing the input and output of the Op Amp alone (Vid1-Vid2 and Vo and not Vsupply and Vo) in a closed loop configuration the phase shift is only 90 degrees? Why it is so?
And the Simulation ...
- 329
2
votes
2
answers
1k
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How to justify that op-amp 1 has negative feedback?
Op-amp 1 is topmost in the schematic below. I used the ideal amplifier method (using A until the end and then lim A->infinity) and also the virtual short method.
But I don't know if that's enough to ...
- 133
2
votes
5
answers
400
views
Can negative feedback in an opamp circuit be applied to the noninverting terminal?
In figure 1, is the feedback regenerative in nature? If so, can I apply a virtual short to solve it?
- 475
2
votes
3
answers
124
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Negative feedback sustainability
If positive feedback makes output exponentially increase and cause instability in an opamp then why doesn't negative feedback make output extremely small and cause the system to collapse?
2
votes
2
answers
147
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Is there also equal voltage on the inputs of an op-amp with a capacitor in the feedback rather than a resistor?
It can be mathematically proven that when we have a resistor in the negative feedback of an op-amp, the input voltages in the inverting and non-inverting terminals get equal.
I'm wondering if we can ...
- 91
2
votes
4
answers
308
views
Op-amp amplifier feedback, offset
The following circuit is a non-inverting amplifier with a normal op-amp. I know how the "classic" one works: Vout/Vin = (R1+R2)/R2. However, there is a third resistor R3. As far as I know, it has ...
- 27
2
votes
2
answers
868
views
Current Sensing with Op-Amp, do I need a shunt resistor in series with the load on the output?
Hi I am building a circuit to measure current draw from a load, I opted for a voltage follower with a transistor and a shunt in between, The transistor is needed to allow higher currents to flow ...
- 866
2
votes
3
answers
2k
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How to identify the circuit has negative feedback or positive feedback?
I am having difficulty in identifying whether feedback is negative or positive (i'm not talking about feedback topology)
My teacher told that there is a method in which, after deactivating ...
user141515
2
votes
3
answers
886
views
Opamp + NPN and MOSFET in the feedback network, how to prevent oscillations
Background
The task is to add an electronic means to limit the power applied to an electric motor in an industrial setting. The operator normally controls the motor power through a lever that is ...
- 5,497
1
vote
3
answers
431
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Why is this digital output circuit non-linear to the load?
I'm simulating a DAC which puts out 0-20mA, but in practice, the output varies depending on the load of 300 ohm resistor. If I using a 1k ohm resistor, then I get a different output current.
If you ...
- 1,388
1
vote
2
answers
8k
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How do we explain the common-mode feedback in an intuitive way?
There are such beautiful circuit ideas that make you hold your breath and admire them silently. Such an idea is the common-mode feedback (CMFB) in fully differential amplifiers. I was not familiar ...
- 19.5k
1
vote
3
answers
3k
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Understanding negative feedback in an inverting op-amp
Below is a basic inverting op amp. I'm having trouble seeing the negative feedback operation.
simulate this circuit – Schematic created using CircuitLab
If I understand the "golden rules" of ...
- 145
1
vote
3
answers
380
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How does an op amp reach equilibrium?
It seems to me that if you try to solve for an Op-amps output (with negative feedback) discretely (i.e. iterating), you never reach equilibrium. Rather, you find the output moves further and further ...
- 753
1
vote
1
answer
205
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Please explain negative bias and "a stronger field to sweep carriers out of depletion"
I want to understand what a comment means, and I couldn't ask in a comment. In this question, someone asked why use an op-amp with a photodiode rather than just a resistor. The answers and comments ...
- 13
1
vote
2
answers
1k
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Op - Amp: Linearity, Negative Feedback and Virtual Short
I need some explanations about Linearity, Negative Feedback and Virtual Short for an ideal Operational Amplifier.
Precisely, I have been always told that an operational amplifier with negative ...
- 3,590
1
vote
1
answer
413
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Single op-amp with "isolated" positive input pin or method to invert the feedback loop?
To improve isolation between the input and the other pins of a circuit, I used an MCP6001R SOT-23-5 op-amp which has a pin-out like this:
I am interested by the fact that there is quite some space ...
- 3,281
1
vote
1
answer
66
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Negative feedback in an opamp
I am a fresher and have been introduced to a basic electronics course at college.
Recently our professor was introducing us to opamps and was referring to negative feedback as a rectification to any ...
- 125
1
vote
0
answers
205
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Op-amp 'overcompensation'
First, a bit of background; I'm trying to regulate a HV DC-DC converter using an op-amp with an NPN Darlington current booster. The DC-DC converter is a push-pull circuit driven at about 40 kHz that ...
user194170