Questions tagged [stability]

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Optimum phase margin Controller Design

I am designing a PI voltage and current Controller (Cascaded Control for Buck Converter with LC filter) and I am confused about what is the perfect phase margin to choose for the application. I read ...
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38 views

'Weaker' feedback reduces DC Gain?

My Understanding From my previous understanding of stability and op-amps, I know that placing an op-amp in a closed-loop configuration reduces the DC gain and extends the 3-dB bandwidth as seen in the ...
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2answers
57 views

SMPS stability near and above switching frequency

I am simulating in LTSpice a switched-mode power supply (LT3845) at a frequency of 150kHz. I am measuring the loop gain at the feedback node according to this article. The way I understand it, the ...
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39 views

About phase margin of inverting amplifiers

Phase margin is usually defined as how far is the phase of the loop gain from -180: $$PM = \angle \text({loop \space gain}) +180^{\circ} $$ Let's suppose that we want to compute the maximum phase ...
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32 views

Why can stability Factor be defined like this ? What does “stability” mean here? let voltage be stable? or let some of current be stable?

i saw some information about stability from here : https://www.youtube.com/watch?v=jw_GUiswndw&t=422s ,but i have some problems,why can stability Factor ,\$S\$, be defined like this ? \$S=\frac{\...
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19 views

PWM switch open loop gain plot buck topology

Open loop gain understanding, without using PWM switch and with using PWM switch model Vramp =1V , Vin =5V, Modulator gain = Vin / Vramp = 5 , Fsw = 300Khz, Vout = 1.8V Above image without PWM switch ...
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29 views

lyapunov function derevation

hi could you please help me to know how did they find the derivative of V lyapunov function
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1answer
43 views

Linear dropout voltage transfer function

I am reading this application note from Texas instrument : http://www.ti.com/lit/an/slyt187/slyt187.pdf?ts=1591543592096&ref_url=https://www.google.fr/. The application note give us the transfer ...
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3answers
36 views

LDO output and input capacitor clarification

I would like to understand how to size the input and output capacitor of an LDO. What I think to know: About the input capacitor: The input capacitor is used for filtering high frequency input ...
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2answers
101 views

Flyback - Stability, Oscillations, Buzzing

I'm working on a dimmable, 60W CV/CC LED driver (ILED = 0.7 - 1.5A, VLED = 40 - 85VDC). I'm having trouble with this driver since it has some issues including: Extreme buzzing (You can hear this from ...
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38 views

LDO datasheet dont provide open loop gain plot

To make LDO stable compensation. How to obtain open loop gain phase plot to compensate LDO, since it is not available in the datasheet. Since its very much required for LDO load transient, load ...
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40 views

Slope Compensation - about the slope value

I read an article on EDN about slope compensation written by Sergio Franco. Here it is : https://www.edn.com/slope-compensation-in-pcmc-dc-dc-converters/ It takes the case of a buck converter. It ...
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1answer
66 views

Strange Error amplifier of LDO

I am trying to work out what function the components in inverter colors serve, this is a schematic I have derived from a net-list to make it easier to explain my answer ...
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1answer
41 views

Help check amplifier stability

I need to do the stability analysis of my amplifier circuit. I implemented schematic in LTspice, where I did some of simulations, so I would like to keep the same tool also for the stability analysis. ...
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2answers
81 views

Bias stabilization of a transistor

The instability of Collector current(Ic) of a transistor depends on three factors viz. Icbo, Vbe & Beta. Can you explain why Vbe decreases(by 2.5 mV/°C) with increase in temperature?
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3answers
46 views

MC34063A switching regulator: LC filter and feedback

The MC34063A bust/boost/inverting switching regulator recommends using an LC filter at the output, after the filtering cap. This LC filter is optional and there is no mention in the data sheet about ...
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4answers
95 views

Audio power amplifier improvement

I need someone to revise/suggest improvement for the audio power amplifier I am designing. This PA is going to be used for driving the horn speaker (8ohm 100W). I decided to start design from scratch ...
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27 views

LDO TPS7A54 Average Modelling

I am trying to do Average modelling for TPS7a54-q1, Looking at the parameters in the datasheet, I was able to find Line and Load Regulation data from which, I could approximate open loop Output ...
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3answers
89 views

Stability of a two poles negative feedback amplifier

let's consider this analysis of a two-pole amplifier with negative feedback (Microelectronic Circuits by Sedra Smith 7th edition): Before showing you my doubts, let's consider this introduction made ...
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1answer
38 views

Finding value of feedback capacitor in a photodiode amplifier

I am tasked with the objective to design a photoelectric sensor. Being very weak on amplifiers & control theory, I am working on the basics of op-amps. Following this reference design by TI, I ...
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1answer
54 views

Op-amp outputs as power sources

I'm designing an audio circuit running on ±15V supplies, which has a need for precision +12V and -5V rails. These must source (from 12V) and sink (from -5V) up to ~20mA to power a CEM3340 oscillator ...
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0answers
47 views

The Effect of Input and Feedback Capacitors on an Operational Amplifier Open-Loop Gain Response

I have the following circuit that I want to compensate: As shown from the step response, the circuit is unstable because of the high input capacitance (the green plot is without any additional input ...
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2answers
59 views

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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64 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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1answer
67 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
113 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
42 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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31 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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2answers
149 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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24 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
962 views

find a point on root locus for specific damping ratio?

Although I have seen many types of root locus plots which have some curved behavior. I cannot find the poles for which my system has a given damping ration of \$ \zeta = 0.59 \$. I need to somehow ...
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36 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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214 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
293 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
79 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
70 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
150 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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144 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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45 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
132 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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150 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
170 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
836 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
75 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
139 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
97 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
69 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
68 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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