Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [positive-feedback]

48 questions
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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 positive feedback is often used to implement a…
Emm386
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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 statements about it: 1. Does the Operational…
Archer Fuyyr
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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 used. How would this affect the signal?
TwoheadedFetus
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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, $$V_o = A\left( V_x - V_i\right)$$ $$V_o = A\left( \frac{R_1}{R_1+R_2}V_o - V_i\right)$$ $$\left( \frac{R_1}{R_1+R_2} - {1\over…
Akash Karnatak
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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 need 3 capacitors to get a 180° phase shift in…
Darko
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1 answer

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 between the output and inverting input. There is also a…
tobalt
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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 (such as the Colpitts oscillator) or by a square…
Kinka-Byo
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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 has two threshold voltages as shown in the…
Sai Sandeep Lolla
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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 which it is then operating in positive feedback.…
mwilliams25
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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 section is describing the problem with unexpected positive…
summeriok
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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 prove negative feedback? simulate this circuit –…
est.tenorio
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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
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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 NOT act as a voltage buffer. However, as my…
nn08
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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 so, this must be the reference voltage too. How is…
across
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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 independent sources, we break the loop and move from that…
user141515
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