Questions tagged [negative-feedback]
The negative-feedback tag has no usage guidance.
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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 ...
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Potential ground loop issue in DC-DC common ground circuit
I am trying to setup a dedicated battery for my dash-camera, this will provide continuous power when the ignition is OFF and has a manual NC switch to turn off the circuit when not needed.
I ...
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3
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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 ...
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Why is the output impedance of an open-loop amplifier with a loading effect calculated by breaking the loop like this?
I'm a bit confused about how the author calculated the output impedance of the open-loop transconductance amplifier with the loading effect as follows.
(All images are taken from of the 6th edition of ...
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7
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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 ...
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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 ...
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4
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I need help to identify the negative feedback loop in a hysteresis comparator
Can anyone help me identify where the negative feedback path is?
I want to determine the feedback factors for both negative and positive feedback, but it's not clear to me where the negative feedback ...
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Why input signal of negative feedback amplifier is Vs - Vf?
The block diagram below is from my textbook. I don't understand why the input voltage Vi = Vs - Vf. Take an example as the image with numbers on it, I know its not correct in reality but just assume ...
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3
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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 ...
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5
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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.
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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 ...
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Negative feedback amplifier
The following circuit diagram is from a book on electronic circuits. The Current source \$I_s\$ is driver of the amplifier. It was written that this amplifier has negative feedback. It seems that if ...
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About stability in system with loop gain AB>1 in negative feedback
I have been reading about stability and feedback systems, and a very silly issue has appeared.
We can describe a negative feedback system as what can be seen in the following picture:
Image source: ...
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4
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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 ...
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What are the necessary conditions to prevent latch-up problem for Oscillators?
In his chapter on oscillator design, Razavi discusses the issue of latch-up and proposes several methods to eliminate it. However, he doesn't provide explanations for these methods. Could anyone ...
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How to analyse this with nullor block?
The first is the schematics from NMOS4 with parasitic capacitance:
I recently read an article on how to analyse the circuit with The Nullor and Some Applications.
The equivalent nullor circuit. I am ...
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The influence of negative feedback on input resistance and bandwidth
I'm interested in how negative feedback affects bandwidth and the cutoff frequency.
Is the cutoff frequency always increased by (1-Ab) times?
fg_r = fgo*(1-Ab)?
Does the same apply to input resistance?...
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How to break the feedback loop and add the loading?
I am trying to break the feedback loop of a fully differential amplifier and add the loading to the input and output:
I want to do this to take into account the loading of the feedback network on the ...
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Gain of a negative feedback circuit (problem)
I am asked to find the gain A for this negative feedback circuit below:
(A: gain, G: all of the gain of the circuit, F: return ratio)
The simplified circuit above shows the gain A that I am trying to ...
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Constant current source with transistor
I have this circuit that should describe a constant current source. From my point of view the pnp-transistor has to work in its saturation mode. Thus the potential on the emitter should be constant. ...
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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
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How to determine if the feedback is positive or negative?
How to know if I have to apply the formula Af=A/(1-AB) [positive feedback] or Af=A/(1+AB) [negative feedback]?
3
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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 ...
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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 ...
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Contradiction between two circuit simulators in measuring open loop gain
I am implementing what I've learned over the past couple of days. This relates mainly to the simulation of a voltage regulator.
I built the (roughly) same circuit in both TINA TI and LTspice to ...
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Why are these voltage regulators seemingly using positive feedback?
Looking over LDO / voltage regulator topologies I keep seeing examples of LDOs where the feedback network is connected to the non-inverting input terminal of the error amplifier.
Like this:
Taken ...
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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 ...
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Linearity and speed tradeoff with closed-loop feedback
This article describes some tradeoffs involved with methods to increase an amplifier's linearity. One of the ways to increase a circuit's linearity is by applying negative feedback, which converts an ...
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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 ...
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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)
...
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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 ...
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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 ...
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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 ...
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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+(\...
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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 (...
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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 ...
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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-...
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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?
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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
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5
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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 ...
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3
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How does this LLC converter keep 50% duty cycle and zero DC offset with AC-coupled feedback?
I'm currently designing an LLC resonant DC/DC converter with 12V input, +/-15V output and nominal 200W combined output power. I've already got my resonant circuit, transformer, gain curves and power ...
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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
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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?
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Modeling first-order dynamics of a switching converter
I have created a simple, first-order model of a switching regulator in steady state (it's basically a transformer with a loss element). Its only parameters are desired output voltage \$V_o\$ and ...
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Block diagram of inverting amplifier
I want to draw the block diagram of a generic inverting amplifier.
simulate this circuit – Schematic created using CircuitLab
Question: What is the actual block diagram for an inverting ...
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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 \...
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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 ...
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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 ...
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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 ...
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How does a capacitor-crystal-capacitor π-network produce a 180° phase shift in a Pierce Oscillator?
The Pierce Oscillator consists of an inverting amplifier, a crystal in parallel with a biasing resistor as well as two capacitors connected between the legs of the crystal and ground, as in the ...
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