All Questions
Tagged with negative-feedback operational-amplifier
95 questions
7
votes
6
answers
887
views
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
4
votes
9
answers
855
views
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 ...
0
votes
3
answers
139
views
What is causing the spikes at the negative terminal of the opamp in response to the square wave?
I have a simple inverting amplifier as following in which the input is a square wave. By virtual short I expect node VF2 to be at 0V, but when I plot the voltage at VF2 I see spikes that are in sync ...
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
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 ...
2
votes
3
answers
248
views
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 ...
4
votes
5
answers
2k
views
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
0
votes
1
answer
62
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Input/Output Impedance for ALI
Consider these circuits from Paul Horowitz "Traité de l'electronique" page.238:
I want to derive the expressions they made for \$ Z_e, Z_s \$ for both circuits:
So I think the op amp is ...
- 119
4
votes
4
answers
674
views
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
0
votes
9
answers
427
views
Why, in a negative feedback amplifier, do the op-amp input terminals become virtually connected?
The equation from the model of the functionality of the op-amp is that
$$V_{out}=A_{0}(V^{+}-V^{-})$$
In case of negative feedback, \$V^{+}=V^{-}\$.
Why do the two terminals in case of negative ...
user344970
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
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
0
votes
3
answers
184
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Minimizing noise with single-ended opamps
Opamps often get used with one input at a DC voltage, usually the main ground per the standard inverting amplifier example:
For low noise, a BJT input stage like OPA1611's is often chosen for the ...
- 728
3
votes
2
answers
909
views
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
0
votes
5
answers
230
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Measuring Inverting Op Amp config and not getting desired output (practice)
I am a year 2 EE student and I'm still struggling with getting simulations to work in practice.
Components:
10k resistor x2
Arduino
LM741 Op Amp (pinout: https://www.ti.com/lit/ds/symlink/lm741.pdf)
...
1
vote
1
answer
66
views
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
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
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
0
votes
2
answers
287
views
Regarding positive feedback and negative feedback of OP-AMP
My background knowledge
This picture is ideal OP-AMP:
where $$Vo=A(V_+ - V_-)...(0)$$
When I configure the non-inverting amplifier mode:
$$(V_i-V_o\frac{R_1}{R_f+R_1})A = V_o....(1)$$
$$V_iA=V_o+(\...
- 661
0
votes
1
answer
87
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voltage follower design question
Hi , I am trying to build a simple voltage follower circuit in IC. I have tried to build ideal Op-Amp as a transconductor. Now, it requires minimum bias voltage for it to operate as a transcondcutor (...
0
votes
0
answers
79
views
Problem with Arduino MEGA and opamp LM741CN for feedback ammeter
I am trying to create a feedback ammeter using Arduino MEGA ADC and OpAmp LM741CN. In order to perform a proof of concept, I use Arduino MEGA, LED, and Resistor 1 MΩ, then I read its current with a ...
0
votes
4
answers
1k
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How does negative feedback stabilize the output of an op-amp?
I am trying to understand how negative feedback stabilizes the output of op-amps.
It is known that Vout = AOL*((V+)-(V-)), where AOL is the open loop gain of the op-...
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
1
vote
0
answers
205
views
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
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
0
votes
1
answer
52
views
Op-amp clarification in table
I'm using this Op-amp with Vcc of 5V and GND, voltage follower configuration.
Input to the non-inverting terminal is 0-2V (from a DAC). Output pin is connected to the inverting terminal.
Since, it's a ...
user220456
0
votes
3
answers
514
views
How is voltage difference of input terminals zero in open loop ideal op amp?
An ideal op-amp has infinite open loop gain. This means that the input voltage difference approaches zero. What causes the difference to go to zero in the absence of negative feedback?
- 147
0
votes
0
answers
111
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Discussion on demonstrating saturation in operational amplifiers with positive feedback, and simulation problems
I have been dedicating my time to the study of Operational Amplifiers for the past few weeks.
I understood that an amplifier in an open loop configuration has a very high gain, in the case \$A \to \...
- 207
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
0
votes
2
answers
173
views
Negative feedback divider calculation for NE5532
I have this "Switched Gain" circuit from Douglas Self's book.
I want to implement the same topology but with different gain in decibels: 0 dB, 3 dB, 6 dB and 12 dB.
I need a method/formula ...
- 291
0
votes
3
answers
411
views
Op-amp output as gate voltage to MOSFET
As I understand it, the MOSFET here provides negative feedback to the closed-loop op-amp configuration. Hence, Vout2 = 1 V.
Thus, the current through NMOS = Id = 1 mA. So Vout1 = 5 - (RD·Id). Then ...
- 17
6
votes
4
answers
606
views
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
0
votes
6
answers
2k
views
None-inverting op-amp must zero output, why not?
simulate this circuit – Schematic created using CircuitLab
In this circuit, the input is continually summing with its negative through negative feedback, so it must become zero on the output. ...
- 547
0
votes
5
answers
513
views
How can negative feedback reduce distortion if A*beta>>1?
I have read that negative feedback reduces distortion (frequency, amplitude, phase) because if \$A \times beta >>1\$ the transfer gain will be \$(A/(1+A*beta)) = A/A \times beta=1/beta\$. Which ...
0
votes
0
answers
273
views
What is the purpose of a negative feedback resistor in a schmitt trigger?
This schmitt trigger is used with an integrator to create a triangle/square wave oscillator but R5 has been added to the typical inverting schmitt trigger topology. I know that in simulation, this ...
0
votes
2
answers
359
views
Feedback amplifiers and their corresponding system block diagrams
I'm a newbie in analogue circuits. I find it so confusing analyzing feedback amplifiers.
The typical feedback systems introduced in textbooks is shown below. The input signal \$X\$ is connected to a ...
- 635
0
votes
1
answer
87
views
How can we confirm whether the op-amp has -ve feedback? [duplicate]
Many text books show an op-amp will have negative feedback when o/p is connected back to -ve input through some discretes and under such condition V+=V- is satisfied for op-amp input terminals.
In the ...
- 3,156
0
votes
1
answer
645
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Preventing op-amp outputs from affecting one another
I built this op-amp circuit that takes in 4 inputs and outputs 3 sums by using op-amp adder and difference circuits to achieve a gain of 2x. In a simplified circuit, I boiled it down to the bare op-...
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
5
votes
4
answers
839
views
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
0
votes
4
answers
2k
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Op-amp with BJT circuit problem
I'm studying for EE final exam
First Question: what is the current through the red LED?
I have been working on this problem. So far, what i got is that with 5V come in the non inverting input of the ...
- 1
1
vote
3
answers
431
views
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
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.
...
0
votes
1
answer
129
views
Understanding Negative feedback loop circuit with an Ideal Op-Amp [duplicate]
The following is given as an example of a negative feedback loop in my textbook, note that the op amp is assumed to be ideal.
However I do not seem to get the logic behind this acting as a negative ...
- 107
0
votes
2
answers
232
views
Understanding Negative feedback loop circuit with an Ideal Op-Amp
The following is given as an example of a negative feedback loop in my textbook, note that the op-amp is assumed to be ideal.
However I do not seem to understand the logic behind this acting as a ...
- 107
3
votes
3
answers
623
views
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
0
votes
0
answers
243
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Op-Amp Summing Amplifier Not Working
I have this below circuit op-amp summing amplifier with its below result:
But in my actual circuit all components are the same except the op-amp.
I am using this op-amp part in my practical circuit :
...
user220456
6
votes
4
answers
5k
views
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
0
votes
3
answers
536
views
Trouble visualizing voltage-shunt mixing
I'm trying to understand how voltage-shunt feedback works in an inverting op-amp circuit. I can't seem to visualize how the feedback gets mixed in shunt with the input.
NB: Before I tried this, I was ...
- 1,221
0
votes
2
answers
535
views
Problem in controlling the device temperature using an op-amp
OBJECTIVE:
I have a device to which voltage is applied and this voltage has to be controlled according to the temperature detected by the thermistor that is placed on the device. If the temperature of ...
