# Tagged Questions

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 ...

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### Working with current feedback opamps [CFA ]

before entering in to problem: my application is a laser pulse detection, in this process when a laser pulse falls on photo diode it generates current, later stages include a I-V conversion, ...
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### Finding Loop Gain (Aβ) of Transimpedance Amplifier

I have been having trouble finding the loop gain (Aβ) of the following transimpedance amplifier: simulate this circuit – Schematic created using CircuitLab To find Aβ, the books I have ...
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### How to calculate the feedback resistors for an SMPS

I have designed an SMPS circuit for my host board. As the datasheet, the feedback resistors are calculated as As per the datasheet, Feedback Voltage(Vref) is 0.6V and I want 4V Output Voltage. ...
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### Finding Feedback Resistance of Op Amp

simulate this circuit – Schematic created using CircuitLab How would the feedback resistance be found in this setup? I am used to seeing the negative-feedback resistance as a single ...
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### Is there a difference between the step response of a first order transfer system and a open loop step response?

The step response basically look the same to me so I am wondering if there is a difference between the two?
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### Feedback loop-gain(beta) derivation for the inverting amplifier?

During my study on the negetive feedback concept, i observed that the beta derivation for the non-inverting amplifier is so evident which is just a potential divider voltage.But i am unable to find ...
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### What is trimmable “peaking”?

I'm studying Jim Williams application note AN-104 - Load Transient Response Testing for Voltage Regulators, in which he describes an FET-based load transient generator, what might commonly be called ...
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### Step-down with external mosfet - why heavy current surges?

I built this circuit, which is supposed to deliver currents up to 20 amps (when everything else works...). The purpose is (eventually) to build a constant current source (as opposed to a constant ...
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### In an isolated SMPS feedback design, how could optocoupler latency be higher than the switching period?

I often see this in practical SMPS designs. An optocoupler & voltage reference pair is used for informing the controller section about the output voltage level. However, when I read the datasheet ...
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### What causes “positive feedback” in audio amplifier

I am currently using an audio amplifier to make a presentation. However, sometimes mid presentation the audio amplifier will go into a "positive feedback" mode where the sound coming out of the ...
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### How to add frequency control feedback loop to a circuit for an inductive heater

I am interested in a design made by an MIT student, Bayley Wang, several years ago for a 30kVA induction heater. One engineer on this site with professional expertise examined this circuit and ...
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### A question about positive feedback resistor in a Schmitt trigger

In many tutorials when explaining hysteresis what I read that when the output is high R3 becomes in parallel with R1; and when the output is low R3 becomes in parallel with R2. Above is a depiction ...
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### Negative feedback - equilibrium

I have a basic question regarding negative feedback and stability. As I've understood it, negative feedback is supposed to promote equilibrium. But suppose we have negative feedback loop block ...
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### Software controlled regulators do I need an MPU or MCU?

I need 10 software controlled DC voltage regulators with digital feedback. The voltage range will be 0-600v and the currents will be 0-100ma (maybe more but not likely) This is what I have now for ...
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### Efficient Single Phase Motor Speed Control

Usually triac based speed control vary the phase angle of firing to reduce the amount of power goes in to motor, and hence control its speed. this is not very efficient method, also it may not be ...
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### Common Emitter Colpitts oscillator

Good day, we were tasked to design a transistor based RF oscillator to be used as a VCO for our design experiment. In the picture shown below I have seen many tutorials on how to set the L1, C2, C3 ...
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### How does this sample and hold circuit work?

What role does the 30k resistor play in the LF398? How would that resistor eliminate any offsets introduced by the op-amps in a circuit like this one: On this ...
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### FPGA design rules - Using a Module Output Register Value Internaly

I'm trying to optimize a verilog code and I found something that I don't feel it's correct. I found a module that has an output and it's using that output value as a condition in a case statement. ...
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### Determination of System poles through open/short circuit time constant technique

I was reading about the open and short circuit time constant technique for estimating the dominant and non-dominant poles of the system respectively. For the dominant pole (open circuit time constant) ...
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### Delay and Stablity in Negative Feedback Systems: Confusion-2

This question is in reference to my earlier question: Delay and Stablity in Negative Feedback Systems: Confusion In that question I wanted to ask why the second order system is always stable. But I ...
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### Selecting a capacitor for use in feedback loop

I'm designing a DC Lab Power Supply; the voltage regulation circuit looks like this: I'm developing the BOM, component by component, and next in line is specifying the capacitor in the feedback ...
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### Adjustable 0-5A voltage controlled current source

I would like to build a high side current source that can source 0-5A with a 1mA resolution. The voltage source feeding into this current source is a variable 0-50V that is always ~3V above the ...
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### Delay and Stablity in Negative Feedback Systems: Confusion

Below is a block diagram that shows an op-amp in negative feedback with feedback network made from resistive divider: The encircled block is Op-Amp with 1 and 2 as its inverting and non-inverting ...
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### Feedback resistance condition (Rf > 29R) in Phase-shift oscillators

In an equal resistance , equal capacitance CR phase-shift oscillator, the feedback resistor has to be slightly larger than 29*R When I am attempting to simulate the circuit at 29*R, there's ...
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### Modeling a feedback loop in spice

I'm having some difficulty with an asymmetric half bridge design. I've never been great with control loop theory, and I'm wondering what the best way to figure out the R and C values for the feedback ...
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### Does movement along the imaginary axis of a root locus change the natural frequency?

I have two root locus plots (x-real, y-imaginary) of the same oscillating mode: (1) for a base case system and (2) a system with added feedback. They are so similar, almost identical that I am having ...
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### Systems stability with zero poles

I have a rather simple question I would say. I know that systems having real poles to the right side of the plane will inevitably be instable (for LTI systems at least). But I'm confused with ...
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### Can you switch between 2 tank circuits using a relay?

Say I have an oscillator that needs to span between 1 GHz and 1 Mhz. Ill be controlling it with a microcontroller, probably an arduino. According to this, ...
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### Bandwidth of inverting and non-inverting op-amps

If the same op-amp is used in both inverting and non-inverting modes (with same closed loop gain using appropriate resistors), will the closed loop bandwidth of the op-amp in both cases be the same? ...
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### How do I take the larger of two analog signals?

I have two feedback signals. I want to create a circuit that outputs the larger of the two. I know I could do this with diodes, but I'm unwilling to accept the diode drops. I suspect some op amp ...
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### midband gain calculation of feedback amp

I cannot wrap my head around this. how did they calculate the gain of Q1? can anyone explain the big picture? the math is already shown but I cannot see the breakdown of it. rpi1=2.3K and rpi2=1.23k ...
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### Help understanding negative feedback & bias design on audio amplifier

Please take a minute to look at the audio amplifier diagram below: In case it helps, the diagram comes from a do it yourself Velleman 7W Mono Aplifier (K4001) kit. The amplifier is based around the ...
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### Gain of Basic Amp with FB network

the goal is to find the gain of the circuit. I don't understand the Vi/Vs part. I know they used voltage divider, but why they included the second term(in Red) in the expression? where does that come ...
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### Is it possible to make a non-inverting amplifier with positive feedback?

The 'classic' non-inverting amplifier configuration uses negative feedback. What happens when the + and - terminals are switched? Based on my pencil-and-paper analysis and a Circuitlab simulation, it ...
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### Have current feedback op amps gone out of fashion?

Or have they perhaps always been a bit of a niche product? I've been working with op amp circuits on nights and weekends for about a year now. It was a fair amount of time before I encountered a ...
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### What is meant by 'modified forward path' in this op-amp problem?

What is a modified forward path? In the practise exam paper I'm doing I'm given this circuit and asked to draw an equivalent circuit of the 'modified forward path amplifier'. I'm told that it ...
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### Why sample current via lopsided resistive divider?

I'm studying the constant-current circuit of the Agilent E3610A 15V 30W DC Bench Power Supply. The entire schematic is at the end of the user manual, but I've redrawn the parts of interest here for ...