Questions tagged [positive-feedback]

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Stability test for Feedback Amplifiers

Does the following simple test deduced from Nyquist criterion also apply to positive feedback case or it needs to be modified? If magnitude of loop gain i.e. |T (jω)| > 1 at the frequency where ...
Matt's user avatar
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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]?
Aaryan Pugarja's user avatar
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1 answer
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op amp positive feedback Schmitt trigger

I have recently come across the op amp Schmitt trigger presented in 3rd edition art of electronics. I decided to build the circuit myself in circuit lab, and I have some questions regarding its ...
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Changing an output signal

I need a way for the rotational hall sensor that outputs 0-5v to be centered at 2.5v and if it goes below 2.5v the output rises. If it goes above 2.5v the output adjusts down. My goal is to have it ...
Taylor Inman's user avatar
14 votes
2 answers
676 views

What is the purpose of the positive feedback in this opamp circuit?

Consider: Attached schematic is from a broken sampling scope that I have in the lab. During the reverse engineering the module, I noticed that it uses positive feedback around U2. I understand that ...
Emm386's user avatar
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Analysis of Op-Amp with Positive and Negative Feedback

I'm trying to understand the analysis of the following schematic: Specifically, the following line of logic Where the authors claim that the transfer function of the LC tank H(jw) is written with ...
TakeMeHomeCountryRoads's user avatar
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stages vs. frequency analysis of ring oscillator

I am currently working on ring oscillators and have stumbled across the following doubt. Upon practical analysis of CS-amplifier based ring oscillators on hspice(the not gates are comprised of CS ...
KaBe2003's user avatar
2 votes
4 answers
255 views

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 ...
summeriok's user avatar
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2 answers
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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+(\...
curlywei's user avatar
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6 votes
5 answers
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Why doesn't the bypass capacitor cause phase shift in this oscillator circuit?

I am trying to understand oscillator basics. I thought I already understood how a capacitor works, but I still get confused about it. This circuit is an RC phase shift oscillator. I understand that we ...
Darko's user avatar
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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 \...
benjamin_ee's user avatar
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Input voltage shift of a comparator

I am working on an envelope detector circuit. The circuit diagram is as shown here: The output of the envelope detector (RC) is connected to the inverting input of the comparator with hysteresis which ...
AlveyFrost's user avatar
6 votes
1 answer
355 views

Opamp voltage follower with weak positive feedback

I am trying to gain some intuitive understanding of the following circuit: simulate this circuit – Schematic created using CircuitLab This is a simple voltage follower with a trace short ...
tobalt's user avatar
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-3 votes
4 answers
361 views

Positive feedback in Op-Amp Oscillators

Is positive feedback necessary in op-amp oscillators? Can you make one using negative feedback?
Jirhs Kumar 's user avatar
1 vote
0 answers
146 views

Lm311 as open loop controller for boost converter

Recently I’ve wanted to make a boost converter. To keep the output voltage stable when a load is connected there need to be a feedback from the output. The circuit above claim that it will keep the ...
Mr. Infinite's user avatar
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The simplest way to keep n-channel mosfet saturated by positive feedback

Actully it will be one way switch for a lamp based on photo-resistor input: To keep the mosfet saturated in the moment it turns on I need positive feedback. How to get it in the simplest way? I can ...
brigadir's user avatar
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4 answers
247 views

Negative resistance in a regenerative radio receiver?

Why is an amplifier with a tuned circuit and positive feedback, such as a regenerative radio receiver, said to exhibit or have negative resistance?
hotpaw2's user avatar
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Can we declare Schmitt triggers to have memory? Can we call their output levels states? [closed]

Are Schmitt triggers able to be declared as having memory? Can we call their output levels states?
ambition's user avatar
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What is the cause of this drastically different simulation behavior with slight variation in capacitor values?

This site uses Circuit Lab's schematic and simulation tool, for which I am grateful. Recently, I was attempting to modify a circuit present in this answer to a question. simulate this circuit – ...
Math Keeps Me Busy's user avatar
1 vote
2 answers
139 views

differential opamp in positive feedback

I am attaching the screenshot of differential op-amp with positive feedback(TLV9062),i am having the doubt ,is the output is same as input with all the same resistor values or any effect with positive ...
maneesha's user avatar
7 votes
4 answers
2k views

Why is this derivation of Schmitt trigger circuit's output signal, incorrect?

This is the reference Schmitt trigger circuit. Using KVL, \$V_x\$ turns out to be \$\frac{R_1}{R_1+R_2}V_o\$. Also, $$V_o = A\left( V_x - V_i\right)$$ $$V_o = A\left( \frac{R_1}{R_1+R_2}V_o - V_i\...
Akash Karnatak's user avatar
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1 answer
197 views

What is the expression for the load current of the following Operational Amplifier circuit?

I have been battling to find the theoretical calculations to find the expression for the load current of the following Operational Amplifier circuit exercise I have in my "Electrical Engineering, ...
Stephan Terblanche's user avatar
2 votes
1 answer
724 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 ...
nn08's user avatar
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2 answers
948 views

Barkhausen Criterion and Loop Gain

Considering the following positive feedback network: Its transfer function is given by: According to Barkhausen criterion, for it to oscillate it is necessary that we have: |AB| = 1 and phase(AB) = ...
Rafael D'Ávila's user avatar
2 votes
2 answers
2k views

Noninverting schmitt trigger circuit LTP, UTP calculation

I knew very well how to work negative feedback using virtual short but this is the first time encountering positive feedback. I think the feedback voltage here is \$\frac{R_1}{R_1+R_2}V_{out}\$. If ...
across's user avatar
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1 answer
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Oscillators shouldn't work

The Barkhausen criteria for sustaining oscillations states that the total phase around the loop must be 0 and the gain must be unity. I was thinking about this and got stuck :) The aforementioned ...
Bran Tran's user avatar
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1 answer
156 views

Concept of Hysteresis and Threshold point in Schmitt Trigger

I understand the concept of Schmitt Trigger where there is 2 transition threshold points so that input changing between the hysteresis would not create output transitions . The very first observation ...
Fawaz's user avatar
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2 votes
2 answers
704 views

How Does the Positive Feedback Bring an Oscillator's Poles on the Imaginary Axis?

In an oscillator, there is a positive feedback that injects energy into the system in order to sustain the oscillations. This feedback places the system's poles on the imaginary axis. I'd like to know ...
Alex L's user avatar
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2 answers
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Discrete-Time versus Continuous Time analysis of feedback system

Imagine a generic feedback system, where A is forward gain and F is feedback gain. I will now go over two cases where in i will analyse this system. 1. Reference = 110, A=10, F=1 In this case, it ...
Omibuddyy's user avatar
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3 votes
3 answers
451 views

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 ...
mwilliams25's user avatar
8 votes
3 answers
944 views

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 ...
Archer Fuyyr's user avatar
1 vote
0 answers
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Unstability condition for positive feedback network involving phase change

For positive feedback: \$G=\frac{A}{1-AB}\$ According to Wikipedia, this system is unstable for AB>1. This condition appears to be for the cases when 'A' and 'B' have real values. But in general, A ...
HIMANK's user avatar
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1 vote
2 answers
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Op-amp circuit to control gain of two analog channels with one single-section potentiometer

I'm working on designing my own headphone amplifier with extremely high fidelity. One thing I want to incorporate is a circuit to control the gains of the two channel's using one single-channel ...
ttshaw1's user avatar
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1 vote
1 answer
522 views

What is topology of feedback for circuit?

I am confused between Voltage Shunt and Current Shunt Also mention why R2 shouldn't be considered as feedback as it is emitter degeneration resistance Consider the above circuit why can't I consider ...
SUNITA GUPTA's user avatar
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1 answer
666 views

How do I find this value for the feedback fraction?

How exactly do I find this value for the feedback fraction Beta? Thank you. \$\omega_0\$ here is the natural frequency calculated as \$\omega_0\$ = 1/RC and s is the complex frequency.
user208480's user avatar
1 vote
3 answers
420 views

Offset voltage comes to saturation in coupling amplifier circuit using OpAmp with Gain=100

I did get in troubles with my student project circuit below! The purpose is to amplify difference between two inputs. Specifically, 20mV and 10mV are connected with input to get 1V at the last OpAmp'...
Thanh Nhon's user avatar
5 votes
3 answers
580 views

Why the Wien Oscillator output is a sine?

I don't understand why the output signal of the Wien oscillator is a sinusoidal waveform. I can easily understand how a sine waveform can be generated by an oscillator which contains an LC circuit (...
Kinka-Byo's user avatar
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Can oscillations happen even if negative feedback is present?

By OPAMP book says that virtual short is applicable in OPAMP only if negative feedback is present an output is not oscillating.I don't get how oscillations can occur at output if the feedback is ...
Buzz bee's user avatar
2 votes
5 answers
392 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?
SUNITA GUPTA's user avatar
2 votes
3 answers
2k views

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 ...
user avatar
0 votes
1 answer
85 views

Misconception in opamp feedback

Is it a misconception that feedback into inverting terminal of opamp is negative feedback and feedback into noninverting terminal will be positive feedback? I feel it is. Because all oscillators have ...
cleverlystewpid's user avatar
2 votes
3 answers
124 views

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?
cleverlystewpid's user avatar
8 votes
3 answers
3k views

Can someone explain this op amp "tone control"?

Its supposed to be part of a guitar effect pedal, why is there positive feedback besides the negative feedback? I was reading about op amps and from what i understand positive feedback is very rarely ...
TwoheadedFetus's user avatar
2 votes
4 answers
2k views

Voltage buffer with ideal Op-Amp (positive feedback) - Instability

I know that the circuits which employ negative feedback are stable, whereas those which employ positive feedback are not stable. How can I prove that a voltage buffer (ideal op-amp) which uses ...
Gennaro Arguzzi's user avatar
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1 answer
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Determining The Polarity of a FeedBack Circuit

In determining the polarity of such a circuit I used the following reasoning: if Vin goes up ID1 goes up and ID2 goes down, ID4 goes down and VG3,VG4 go up because of PMOS, then Vout goes down, if ...
user8925869's user avatar
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Determine if feedback is negative or positive?

Is there a way to know from how a circuit is designed that is has negative feedback or positive feedback. Here are some examples: Example 1: Example 2:
user4826575's user avatar
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3 answers
3k views

Confusion about positive feedback condition in gain equation

Closed loop gain A' of the above op amp system is given as: A' = A / (1 + β*A) where A is the open loop gain which is a positive huge number. Here as a side note, my understanding is that β being ...
user1245's user avatar
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1 vote
3 answers
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Feedback factor of Armstrong Oscillator

I am trying to find an equation for the feedback factor of an Armstrong oscillator in terms of the transformer inductances and I can't find one in books. Am I correct if I say that the feedback ...
DorkOrc's user avatar
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1 answer
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What if you alter a differential amplifier by giving it a positive feedback rather than a negative feedback?

Figure 1 In the above Image 1, you see is a differential amplifier . It has a negative feedback as required. Now take a look at figure 2 below. Figure 2 Lets take a look at figure 2. Now that I ...
Amy's user avatar
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1 vote
1 answer
586 views

What's the purpose of the 'positive feedback resistor' in the circuit

There is a 1M Ohms 'positive feedback resistor' in the 10mA current source below: What's the purpose of it? Update: Some people just think it's not a 'feedback' but simply a resistor tied to ground,...
diverger's user avatar
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