Questions tagged [negative-feedback]
The negative-feedback tag has no usage guidance.
196 questions
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Illustrating op amp feedback without control theory
We are teaching op amps in a high school class, before calculus. So we can't use control theory to teach how op amps respond. All the same, I would like to have an intuitive explanation for how a ...
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6
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What's the intuition for reading transistor/resistor circuits?
The below circuit supposedly provides constant current to an LED. I tested using everycircuit.com and that seems correct (used R = 70 ohm for example).
What's a step by step way of thinking about the ...
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4
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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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3
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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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10
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2
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Another Failed Differential Amplifier
This is the circuit I made - designed it, calculated it, built it:
simulate this circuit – Schematic created using CircuitLab
Q1's and Q2's collector current was 5mA, while Q3's was 1mA. Sine ...
- 2,452
9
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3
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851
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Irregular common emitter amplifier design
Would anyone know of any merits (or demerits) to the common emitter amplifier represented in Figure 1 in comparison to one of a regular pattern (Figure 2)? Thanks.
(The 'DS548' transistor in Figure 1 ...
- 548
8
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2
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Emitter follower
I'm having a hard time understanding an emitter follower. What I don't understand is why there is no voltage gain but only current gain. From my understanding when the transistor is turned on, the CE ...
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8
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3
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610
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Confusion regarding signal amplifier
Can anyone explain to me why the node voltage between the collector of Q1 and R1 have its signal amplified while for Q2, the node voltage at R3 and emitter does not have its signal amplified? I read ...
- 609
8
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3
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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 ...
- 83
8
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2
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White and Pink Noise Generator Circuit - Cryptic AC Analysis
The “Electronic Devices and Circuit Theory” book (by Boylestad, Nashelsky) gives a brief description of a random noise generator circuit at the end of “BJT AC Analysis” chapter. (Btw, exactly the same ...
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Why is inverting op-amp behaving like a low pass filter?
can anyone explain why this circuit behaves like a low pass filter despite having no capacitor in the feedback loop?
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6
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How is this op amp in negative feedback?
I'm trying to solve this question for homework but they mentioned the first op amp is in negative feedback. How though?
Is it because of the output of the second op amp (OA2) is also in negative ...
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7
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7
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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 ...
- 1,116
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5
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Is transistor in cutoff?
In the following circuit, consider the op-amp to be ideal (gain = ∞ , input resistance = ∞) and transistor beta is 20 A/A
Initially I was using virtual ground concept here but in the given answer ...
- 71
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Highly Distorted Output of Class B Power Amplifier
This is the circuit I made:
simulate this circuit – Schematic created using CircuitLab
This simple circuit incorporates differential stage - VA (Voltage-amplification) stage - OPS (Output ...
- 2,452
6
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5
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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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What's the need for a small capacitor in the negative feedback parallel to a feedback resistor?
I have the following circuit:
I think I understand pretty much all the aspects of it except for the small capacitor in the feedback. What is the need for it? Judging by the frequency of 1 MHz that is ...
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How does the op-amp stabilize?
I have a problem understanding one thing in op-amps, namely - when the cycle of stabilizing ends?
For example, when we have simple non-inverting amplifier, firstly the difference equals the amount of ...
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6
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4
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Using an op-amp in an unusual configuration with (inverted) negative feedback to the non-inverting input
Here is a question for those who understand unusual, non-conventional op-amp configurations.
Is there any reason an op-amp can't be configured with an input going to the inverting input, and the ...
- 63
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6
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How does opamp open-loop gain affect closed-loop gain in a circuit?
The gain of an opamp circuit is basically $$A_v=-\frac{R_f}{R_i}$$
But how come the gain of the opamp itself does not appear in the equation? How is the opamp amplifying anything in the circuit? What ...
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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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In a negative feedback loop, why does increase in v_out lead to increase in v-?
I hope this is the right place to ask this question. (Please let me know if there's a better place to ask this.)
Basically, I'm quite confused about how we check if we have a negative feedback loop.
...
5
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4
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837
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OpAmp with common-mode voltages and zero feedback current
Circuit A is a classic non-inverting amplifier with a common-mode DC voltage 1 V to both its inverting and non-inverting input. Since 1 V has to appear at the inverting input, there is no voltage drop ...
- 1,448
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4
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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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9
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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 ...
4
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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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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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5
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Understanding Op-amp Negative Feedback
Have a look at the diagram above. It shows an op-amp with negative feedback. Ignoring the feedback loop for now, the voltage (pressure) coming from the 5V battery, acting on the inverting pin, ...
- 1,696
4
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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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What happens to output if OPAMP its supply is tweaked?
Say the above OPAMP is normally operated with supply of +15V and -15V and output is said to swing from +15V to -15V. But I changed -15V power supply {of OPAMP} to -14V and Vi to:
(a)1V
(b)-15V
(...
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4
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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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4
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2
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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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Using an op-amp to drive LEDs according to an incoming signal
The following schematic was suggested for visualizing the frequency (which is variable) of an oscillator using two LEDs that light up alternatingly. It seems that the value of the resistor determines ...
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1
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568
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Feedback in LM2574
I wonder what is the purpose of 'R66' at the feedback terminal of LM2574? I have seen its datasheet but I cannot find info about this. Instead of a single resistor there is a voltage divider shown in ...
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Art of Electronics Ex.2.20 Series negative feedback amplifier
Here is the exercise followed by a schematic:
Applying the techniques we used earlier, one can show that G(open
loop) ≈ 200, loop gain ≈ 20, Zout(open loop) ≈10k, Zout(closed loop) ≈
500Ω, and ...
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2
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Cannot predict closed-loop gain of this amplifier
This is the circuit I am currently analyzing: (link to LTSpice file)
I am trying to predict each stage closed loop gain and overall gain (with all loops closed).
First thing I did is calculate DC ...
- 2,452
3
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3
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527
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Understanding the biasing of a transistor with negative feedback
I am trying to understand the following circuit.
However, I don't understand this step in the accompanying explanation:
"A transistor with a large gain will cause a large voltage drop over the ...
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3
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3
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How to calculate closed-loop bandwidth from open-loop parameters using feedback factor
I'm working through a past feedback analysis question for an exam and trying to calculate what the closed-loop bandwidth becomes given the open-loop gain \$|Av|=10^5\$, open-loop bandwidth \$B_{wo} = ...
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3
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Why doesn't the following circuit have negative feedback?
Consider:
The Sedra book says that it's a Schmitt trigger, so there is positive feedback, but why doesn't it have negative feedback as well?
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3
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2
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Can an open loop system replace a close loop system
I'm thinking about a mathematical possibility how an open loop system can replace a close loop system so here is my explanation
Let's say I have a plant with transfer function as given in image (1)
...
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3
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4
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Negative feedback perspective on SAR ADC
A SAR ADC resembles a negative feedback system. The comparator input is a summing node.The difference between the analog input and the DAC output is the error signal which is driven to zero by the ...
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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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2
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909
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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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How does negative feedback reduce noise?
It is a well established fact that negative feedback improves a lot of parameters related to amplification.
Effect of negative feedback on some of the factors such as gain, input and output ...
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2
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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 ...
3
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1
answer
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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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3
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2
answers
153
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Operational Amplifier - Virtual ground
In the question above I was asked to solve the general shape of Vout, and the exact values in t=0.5ms,1ms.
My question is - can I approximate a constant virtual ground in the negative input of the ...
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3
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3
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830
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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 ...
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2
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Negative feedback from block diagram to circuit components
I can read and understand the block diagrams which show the internal amplifier and the feedback network and I can read and understand the schematics of several single-BJT amplifier circuits, but I ...
- 1,221
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1
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FET based "zener amplifiers"
About the following circuit:
*source: https://youtu.be/niZizzHBanA?t=1779
It is described as a negative power supply, where R1, R2, Q1 and Q2 form a current sink and Q3 "amplifies" the zener voltage,...
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