Questions tagged [feedback]

Feedback is a process whereby information from an output of a signal is used (intentionally or unintentionally) to alter the input of the same signal. Commonly used in operational amplifiers. An everyday example is the high-pitched audio frequency heard when a microphone picks up audio from its own amplified output.

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How does the feedback circuit of this mini USB adapter work?

Summary I came across an old Apple mini USB adapter CLONE. It even had the green dot from the 2008 recall, so it's about a decade old. I'm actually glad I took it apart because one of the prongs fell ...
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Feedback circuit for implementing CC/CV in DC/DC switching circuits

My goal is to design a 10s lithium battery charger with the ability to vary the output current depending on what power adapter is used. For this I want to use the LTC3786 boost converter and the ...
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Feedback impact of collector-base shunt resistor in common emitter amp stage

I made this 3 transistor Rf amp which works well at 10 MHz and has 50 ohm output impedance, a gain of 8.2 (18.3 dB) and quiescent curent of 28.6 mA. It consists of a common emitter stage followed by 2 ...
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7 votes
4 answers
402 views

Is my summary of parasitic oscillation in op-amps wrong?

We were discussing negative feedback in op-amps with my community college instructor. I tried to learn ahead about the concept of parasitic oscillations in feedback circuits. I wrote a summary of what ...
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Feedback loop gain not as expected in a differential amplifier

I am trying to build an approximate opamp with a differential amplifier and add a feedback loop to get the approximate wanted gain. I used a differential amplifier with a current source and a current ...
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6 votes
5 answers
776 views

How to find the gain of an inverting amplifier in terms of feedback?

I have been struggling to answer this question from The Art of Electronics where it asks me to find the closed loop gain of a non-inverting amplifer in terms of feedback and says that the derivation ...
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Flyback: opto/Zener feedback circuit

Could someone explain the difference between these two flyback feedback circuits, and how the second circuit works? Any application note available would be a favor for me.
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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 ...
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1 vote
2 answers
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Help Understanding Opamp Topology (Infinite Gain Multiple feedback with Resistor to Gnd?)

I ran across the following band-pass circuit and I'm not entirely sure what R14 is doing here. The following is a screenshot: For some context, the supply is a ...
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1 answer
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Feedback resistor and capacitor calculation for transimpedance amplifier

I am designing a transimpedance amplifier using LTC6268-10 from Analog Devices. The photodiode that I use is S9055-01 from Hamamatsu and the laser source that I use has a power of 10mW with the ...
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2 answers
80 views

What would the output impedance of the circuit below be?

My analysis is as follows, the auxiliary amplifier with input Vb is being used to sample the output current of the main amplifier (NMOS on the bottom) and return a voltage to its gate. So it is ...
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1 vote
2 answers
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Time optimum controller

I have a question regarding time optimization that I would be very grateful if you could guide me on it. The question is moving a car/mass with nonlinear forces acting on it from point A to point B ...
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5 votes
2 answers
168 views

Role of feedback capacitor in nanoamp current source

I am designing a nano-amp current source to drive a capacitive load, which can vary from about 50 pF - 200 pF. Analog Devices has a helpful application circuit in a datasheet (page 14) for the LT6082C ...
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Is it ok for the one output of a dual-channel op-amp into an input of the other channel on the same IC?

So I have an LM358 op-amp with 2 (as far as I'm aware) separate channels. I need to increase gain but also need to have enough current to activate a diode. The problem is that the device (sensor) ...
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2 answers
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High-side current sensor causing feedback oscillations during overcurrent

I'm trying to design a circuit which uses an INA138 current sensor to shut off a load during overcurrent conditions (max current = 1A). However, when the current is over 1A I'm creating a feedback ...
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DC-DC converter/step down layout improvements/feedback

I'm designing a board with a 12V to 5V DC-DC converter circuit and I would like some feedback on how it can be improved. As it is the first time I have designed such a circuit, I'm not the most ...
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Correct application of Miller theorem on a feedback two-stage transistor amplifier

I'm trying to estimate the lower cut-off frequency of this two-stage amplifier with feedback, assuming a dominant pole exists at low frequency. To do that, I want to apply the Miller theorem on the ...
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2 answers
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Tricking feedback of a buck converter

I need to trick the buck converter feedback. The converter that I am going to use is TPS40192DRCT. Instead of the regular resistor divider, I want to feed there voltage proportional to current ...
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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 ...
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1 vote
1 answer
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PFC voltage loop bandwidth

I have two questions about PFC control problem. 1.) For PFC application, the current loop bandwidth needs to be high. But I don't understand why voltage loop bandwidth needs to be slow. What's the ...
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Haptic feedback from DC motor

I want to make a simple lever connected to a DC motor pressing down on surfaces with different rigidities. I will control the lever up and down to the same position while observing the torque (or ...
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0 answers
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Feedback network of transconductance amplifier with capacitor

simulate this circuit – Schematic created using CircuitLab How do I work on circuits that have capacitors as part of their feedback network? How can I calculate the feedback factor of the above ...
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1 answer
64 views

Flyback primary side control

I read the LT3573's datasheet, I have some questions would like to ask. Based on this block diagram, 1.) What's the main function of the below circuit (red circle). 2.) If I need to detect the output ...
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Fully Differential Amplifier With Common Mode Feedback Network

I need to design the following circuit in a way that can provide a gain of 1000 and also has a power dissipation of 1.8 mW which, according to my calculations, results in a branch current of 250 μA. I'...
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1 answer
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Switching voltage regulator - exceeding output voltage limits

I have been designing a digitally adjustable step-down voltage regulator. Mainly because of the availability and price I chose: MCP1612-ADJI/MS I followed the datasheet and created the following ...
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System level behavioral model for PSSR of a switching regulator

In a design I have a switching regulator (buck for the sake of my example). The switching frequency is much higher than the frequency range of interest and can be safely ignored. However, the input ...
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Quick state feedback controller question

If two estimators where used in a state feedback system, one with error dynamics poles at -10 and -9 and another one at -80 and -90. Which system will give you a better overall performance?
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-3 votes
4 answers
212 views

Positive feedback in Op-Amp Oscillators

Is positive feedback necessary in op-amp oscillators? Can you make one using negative feedback?
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0 votes
2 answers
63 views

Bode's Method of Feedback Analysis for Multiple Loops

I'm studying Chapter 8.6 of Razavi's Analog IC Design textbook (Bode's Analysis of Feedback Circuits). Bode's method provides a way of simplifying feedback analysis by replacing one dependent source (...
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What is meant by "Kelvin connected to capacitor" in layout terms?

In the MPS5496 PMIC layout guidelines on page 37, they mentioned that you should connect the feedback pins to the buck output capacitor "kelvin connected." What does that mean? Can anyone ...
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6 votes
3 answers
479 views

Class AB power amplifier from "Electronic Devices" by Thomas L. Floyd

I am an electronics engineer. I work as an industrial automation engineer in industry. As an electronics engineer, I love amplifiers and other stuff. I was reading Electronic Devices by Thomas L. ...
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1 vote
1 answer
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Single-loop (PID) vs Dual-loop (i.e P-PI) servo position controllers difference?

I am wondering why the servo position loops are mostly dual-loop consisting of position and velocity loops while the position can be controller by using only the position PID controller. I am aware ...
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1 answer
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What is the function of emitter biasing of a transistor?

I have been reading about transistor biasing to counteract inaccuracies in transistor manufacture, add stability etc. One circuit I can't see the benefit in, which is diagrammed in the datasheet for ...
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1 answer
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How to control voltage using PID when driving SCR?

I am designing a scr based digital battery charger for the first time and have successfully driven scr to provide 110V-DC from a 140V singe-phase transformer. 2 SCR-diode combination forms full bridge ...
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4 votes
1 answer
137 views

Designing a small footprint DC/DC converter

This is my first time diving into DC/DC converters, so I'm learning a lot of new information and am aware that I may miss some important details. I'm hoping that others with more experience could ...
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1 answer
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What is the difference in these feedback configurations

In both these cases, the feedback remains the same hence the relation between input and output must be the same. However, if I want to analyse the closed loop stability, will the additional \$K(s)\$ ...
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2 votes
4 answers
347 views

Why is the output of an Op-Amp given by the open loop gain multiplied by the input differential voltage

When designing op-amps at the transistor level, the op-amp output is given by: vout = Aol(vinp - vinm) where vout, vinp and vinm are small signal changes in the output and input voltages. How come ...
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3 votes
6 answers
1k views

How does a unity gain buffer work?

Say we slow down time to a crawl, and turn on a power source connected to a unity gain buffer. Initially, the non-inverting input receives the signal and the inverting input receives nothing, so the ...
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0 votes
1 answer
32 views

Proportional gain with DC offset in LED driver circuit saturates output

I have a negative feedback loop with \$K_P = 10\$ for a LED driver circuit: I've used \$R_{fb} = 9k\$ and another resistor from the LED to the negative terminal of \$1k\$ in order to get a ...
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2 votes
1 answer
282 views

Range of feedback resistor value in non-inverting op amp

Is there any limitation for the range of the feedback resistor in a non-inverting circuit? What happens if I choose feedback resistor very high or very low? What is wrong with choosing a 10M ohm ...
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-1 votes
1 answer
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Do I need to regulate the output of a forward converter?

I'd like to know if a forward converter will maintain a nominal output on the secondary side. For example if I wind a powdered iron toroidal core with 1:10 turns ratio, the 1 being the primary, and I'...
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5 votes
2 answers
711 views

Common Collector Colpitts Oscillator - Feedback analysis

I am a student working on a project where we are using CC Colpitts oscillators as local oscillators. We've chosen the above values based on the condition gm > w02C1C2RL,series, which for the given ...
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0 votes
1 answer
273 views

How to set up an LTSPICE test bench for Common Mode Feedback Loop Stability

Suppose we are given a fully differential (low voltage single supply) op amp with common mode feedback. It is common knowledge to break the loop in order to measure open loop ac performance for loop ...
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2 answers
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Solve opamp with feedback without using virtual ground

Can we solve this circuit without using virtual ground or not? I attempted to calculate the feedback voltage by division of voltage in \$R_f\$ and \$R_{\text{in}}\$ but is \$V_f\$ equal to: $$(V_o - ...
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1 vote
0 answers
60 views

Why does input DC supply gets short circuited when operational amplifier is connected at the output of LLC resonant converter?

Following is the block diagram of LLC resonant converter, more clear circuit can be found here. This is an LLC resonant converter which produces 250V across RL with 50V at input without any issue. ...
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0 votes
1 answer
56 views

Converting dry contact to momentary switch with feedback [closed]

I need to adapt a fan that is turned on/off with an SPST momentary switch to also work with a dry contact. Additionally, I need to ensure that the desired fan state is reached when the dry contact ...
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Feedback Topology - MOSFET in feedback network

i have the following circuit: The feedback network consists of M4, which is biased in triode region. I know the concept behind Feedback Topology and the differences, but I can't figure out why this ...
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Anti integral windup method for analog integrator

I have found the following topology for an integrator/lowpass filter in a feedback system in an existing circuit . I know that the transistors act somehow as a limit of the amplifier, but I am not ...
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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-...
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0 votes
1 answer
117 views

TL494 error amplifier pin maximum voltage input

I'm designing a 60V SMPD for my CNC milling machine using a TL494. I've have successfully driven the gate drive transformer which can in turn drive the MOSFETs. I am able to get 60 up to 70V output ...
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