Questions tagged [stability]

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Placing an RLC input filter at the input of a buck

Since bucks have current spikes at the input side, it's best to use an input filter as you get better noise reduction than using an output filter (afaik). Using a regulator IC however, that is, one ...
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26 views

How do integrators affect encirclements in the Nyquist plot?

I am trying to write a program to determine the closed-loop stability of a system using a frequency response function for data-driven control. I count the number of clockwise(CW) or counter-clockwise(...
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33 views

Why 180 degrees of phase margin should be considered?

We've had one feedback on the phase difference, with the gain as 1. At 300 to 60 degrees, there's just a phase difference, and 61 to 299 degrees, the output is larger. Shouldn't we consider an angle ...
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2answers
69 views

Frequency compensation and feedback capacitance

I was reading the chapter of Microelectronic Circuits (Sedra Smith) about negative feedback systems, and it shows an example of Miller frequency compensation with the capacitance Cf shown in the ...
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1answer
36 views

How do I find value of gain that stablizes the system from root locus?

Consider the following root locus: which is obtained by the following code: ...
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28 views

How to know whether filter is stable given in- and output shapes?

I have this filter with $$H(z) = \frac1{0.5z^{-1}}$$ How can I know whether this filter is stable given that \$x(n) = a^nU(n)\$ and \$y(n) = -a^n U(-n-1)\$?
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67 views

Nyquist stability criterion for positive feedback

it is known that the stability of a system with negative feedback may be analized through the Nyquist stability criterion, which is based on observing the number of turns around the point (-1;0) in ...
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19 views

Finding E for generator given active power and power factor in three phase system (fault analysis)

Question:The generator is delivering 0.5pu active power to infinite bus 3 at power factor 1.0. The system experiences three phase fault on one transmission line very close to bus 2 which is cleared by ...
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21 views

Parameter range to ensure stability using Routh Criterion

I have a question regarding Routh Stability for a characteristic equation of the form, $$ 2S^4 + 2S^3 + 4S^2 + (k+1)S + 4 = 0 $$ I need to find the range of K for which the system will be stable. ...
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1answer
94 views

find a point on root locus for specific damping ratio?

I have faced many type of root locus which some of them have curved behavior. I cannot find the poles for my system that has damping ration without using MATLAB. I need somehow to find the ...
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25 views

What is the Intuition behind the Stability Factor (K) in Microwave Amplifiers?

In microwave amplifier design, there is a Rollett's stability factor (included below), which determines if the amplifier can be unstable. If K > 1, the amplifier is always stable, and if not, it could ...
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2answers
88 views

Stability of Differentiator Circuit

let's consider a generic differentiator circuit, i.e. a circuit whose transfer function is \$\text{constant}\cdot j\omega\$. For instance, you may consider this circuit with Op-Amp: I was reading ...
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2answers
123 views

Resistor parallel to optocoupler LED in Zener-stabilized circuit

I was watching a video about phone chargers where the following schematics was presented: simulate this circuit – Schematic created using CircuitLab In the video it was stated that this ...
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1answer
72 views

Stability of SMPS designed for a motherboard

Many books have covered the stability of many configurations of switch mode power supplies and they have given details on how to set the poles and the zeros of the compensator to make the the power ...
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1answer
30 views

temperature stability in current mirrors

I have read here that temperature stability is one of the performance issues in current mirrors. Can anyone what does temperature stability mean in current mirrors? Thanks.
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1answer
132 views

Does this Root Locus analysis contradict my understanding of Nyquist stability criteria?

I have been trying to theoretically analyse the operation of a 741 op-amp from a stability point of view by firstly deriving its open-loop transfer function. Here is the magnitude plot of a 741 op-...
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16 views

Root locus vs routh hurwitz criteria?

What is the difference between root locus and routh hurwitz criteria? As according to layman knowledge, both techniques are used somehow to determine
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34 views

Does having negative PID gains effects stability and realization of system?

Can we have a PID controller which has positive I gain and negative P gain? or will our system and controller will be not be realizable and will be unstable in this case due to a negative value of PID ...
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1answer
70 views

Relation between stability and overshoot?

Is there any relatonship between stability and overshoot? I mean, can we say that a system if it is marginally stable, it will not have overshoot?
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1answer
104 views

Circuit stable in the Bode diagram, unstable in step-response

I am designing a simple current control circuit and trying to simulate it in LT Spice. The circuit is not optimized for some real-world application, it's more a learning method for me to get grip on ...
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1answer
121 views

Feedback resistors and op-amp instability

I am a building a circuit which has a differential amplifier part. To keep things simple I have simplified the circuit to only show the relevant part below. One thing from op amps which is still ...
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3answers
278 views

Switching frequency and controller's crossover frequency in DC-DC converters

In the context of control loop stability of DC-DC Converters, A switch mode power supply is essentially a sampled-data system, therefore the theoretical maximum bandwidth is one half the switching ...
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1answer
63 views

Bode Plots and Electrical Circuits - Zeroes and Poles

I would like to understand more electrically with little math (transfer function) involved regarding Poles and Zeroes in a control system (Feedback in DC-DC Buck Converter to be specific). I ...
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3answers
123 views

Stability - Driving a Capacitive Load

I know I have been asked not to provide video links and ask questions. But I have no proper guide/mentor or anyone who can provide me better answers other than users in this site. So, please pardon ...
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55 views

Simple Stability and Feedback

I have a question, my book says that for the system in this picture: If the system has G(s)*H(s) with a module of 1 (0dB) and a phase of -180°, the system is in Simple Stability, so it is like in ...
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1answer
51 views

Relationship between switching frequency and controller's crossover frequency in DC-DC converters

I am reading some answers related to my questions based on control loop stability of SMPS. I came across this question. The accepted answer states: A switch mode power supply is essentially a ...
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1answer
57 views

Control Loop Stability of DC-DC Converters

I am performing a control loop stability test on my 5V DC-DC Buck Converter with the help of this Keysight App Note I understand that we are injecting a noise signal on the feedback network of this ...
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1answer
62 views

Beginner's power supply design

I'm trying to design a bench power supply that can be easily controlled by a microcontroller and is more efficient than a simple linear design (although crazy-high efficiency is not the primary target)...
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1answer
76 views

Bode plot gives negative stability margins for a stable plant

I have a plant whose transfer function has all the poles in the left half of the s-plane (obtained the poles using Wolfram Alpha). However, its bode plot gives negative phase and gain margins; I ...
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1answer
71 views

Effect of zeroes in stability

I thought earlier that zeros have no direct effect on stability but when I read the below article of Wikipedia where it said under the heading "Effect of poles and zeros " It says that adding zeros ...
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52 views

Unused BJT in a dual package - Need to do anything for stability?

I am using several NPN/PNP pairs in a circuit. One of the NPN is left unused. Do I need to do anything, or just leave all 3 leads of NPN floating or I need to connect them for improved stability? If ...
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1answer
88 views

Op-amp inductive output impedance oscillation

In Learning the Art of Electronics pg.362, the author presents an op-amp follower driving a long cable. I don't understand the explanation given for the cause of oscillation. In particular, the author ...
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65 views

Unstable current source when reaching a certain threshold in current draw

I’m currently building a system for automated testing of ECUs. It consists of an ECU with regulated loads connected to its power outputs. The other IO of the ECU is connected to an IO expansion card. ...
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40 views

Control Loop Stability - Crossover frequency

I am testing the control loop stability of a DC-DC Converter. One of the Pass-criteria of the DC-DC Converter states, "Cross over frequency should not be higher than 1/8th of switching frequency" ...
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38 views

What is the Rseen from this node?

In the text book I am reading (CMOS Analog Circuit Design by Razavi) the author wrote that the Rseen from node N is (1/gm7), however when I derived it myself I found that the Rseen is ro4 // ro6 (...
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1answer
47 views

Question about feedback in a current reference

I'm studying the following Vbe-based current reference: The author of my book says: Observe that the circuit has two feedback paths around the gain stage. One positive, the other negative. ...
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49 views

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 ...
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50 views

Gain margin using Root locus plot

How can I find Gain margin of any control system given its polar plot In schaum's series I have read that Gain Margin=Ku/Ki but in given figure the system never becomes unstable so shouldn't Gain ...
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87 views

Opamp isolation resistor calculations for a capacitive load

I want to add a capacitive filter for pulse shaping to the output of a transimpedance amplifier using an OPA847. Without the filter, the amplifier works great. With the filter, I get some ...
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1answer
49 views

Abuse TS339 comparator channel as a voltage multiplier

I have multiple free channels of a TS339 amplifier remaining and would like to use one of them to multiply voltages like this: simulate this circuit – Schematic created using CircuitLab Now it'...
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2answers
48 views

MOSFET Capacitance clarification

2 part question here. Are there ways to directly test the input and output capacitance of a MOSFET, Ciss and Coss? On that note, due to internal inductance and capacitance, is it possible for a ...
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90 views

Phase margin Vs damping ratio: Intutive explanation

While designing the compensator for SMPS we always talk about the relation between phase margin and damping factor( or Quality factor). I don't completely understand how damping plays such a keyrole ...
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2answers
85 views

Stability and Positive/Negative feedback

I often read that positive feedback is used to get oscillators (since the output of the circuit is summed up to its input signal and so leads to instability), while negative feedback to get amplifiers ...
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79 views

Understanding a ZVS Oscillator in-depth

For a project I've been building, I've been using the (overused) ZVS oscillator that can be found online. So far it's been working great transferring power wirelessly, but I'm interested in ...
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45 views

Stability of Buck Converter when output capacitance is variable

I am designing a buck converter for an application that has several different loads. Depending on what devices are connected, the capacitance seen at the output of the buck converter can vary ...
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3answers
113 views

Bandwidth and stability of nonlinear circuit

I'm designing an antilog amplifier which produces an exponential output (0.4 mV to 4 V) for a 50 Hz sawtooth input waveform (4 mV to 4 V ramp). If this were a linear circuit, I could determine the ...
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3answers
131 views

LED brightness stability issues - how to fix?

I am performing an imaging experiment in which LED stability is critical. I use 2-3 red LEDs to illuminate a surface while imaging that surface. In each LED circuit, I use a constant-voltage ...
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4answers
115 views

Negative feedback and op-amp poles

I'm trying to get a better understanding of frequency compensation for op-amps. I'll start off with a very specific questions and then get into the context. For a certain op-amp, open loop gain is ...
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142 views

Could i get some circuit design feedback?

I have a computer science background and this is the first circuit I've ever designed. It is a lot of fun designing these circuits, but it also always feels like I'm missing a lot of "obvious" common ...
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68 views

Voltage regulator feedback circuit and stability analysis?

I have been analyzing following buck-regulator circuit to calculate the phase-margin and gain-margin. Circuit Diagram: Buck regulator with input voltage = 12 V and output voltage = 3.3 V. Just as ...

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