Questions tagged [stability]

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What information Bode plot does NOT present?

The classic Bode plot (2D Bode) represent value of the transfer function (a complex number) evaluated at \$j\omega\$ (imaginary axis). It provides information on system closed-loop stability margins ...
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1answer
101 views

Stability of input filter in SMPS - Theoretical explanation

I read the Application note Wurth Electronics ANP008c about negative resistance of a SMPS input and how to avoid oscillation when using an input LC filter. I'm asking for a theorethical clarification ...
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3answers
93 views

Amplitude stabilisation of LC oscillators

Like diode stabilisation and FET stabilisation in RC oscillators, what methods are used for the stabilisation of amplitude in LC oscillators? I have found it very difficult to obtain a clean sinewave ...
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1answer
57 views

Balancing a stick using two different designs and comparing both

I want to understand which feedback systems are in general preferred over another model (that I'm going to show in image),so first we take a example of a particular system (here stick at 90degree from ...
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52 views

How is this amplifier stable at 1GHz

The task is to design a amplifier for maximum gain, which means conjugate matching. The S-parameters at different frequencies are as follows Now for 1GHz $$K<1 \text{ and } \left|\Delta\right|<...
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63 views

Nodal voltage magnitude properties of electricity distribution networks

I am wondering how to know about an electric bus according to its measured voltage magnitudes (possibly and its corresponding real power injection profile). Following assumptions can be made: One ...
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1answer
48 views

Using single-loop analysis in multi-loop structure

Here is regarding Kenneth Kundert's explaination of the loop based stability analysis Two factors affect the applicability of this circuit: the local return loop inside the transistor and the reverse-...
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1answer
48 views

Small-signal analysis of transformer BJT oscillator

In an attempt to improve my circuit analysis skills, I've been trying to understand how this photo flash charger circuit works. I am mainly focusing on the oscillator part on the left, which I've ...
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2answers
112 views

Making a linear regulator oscillate

I want to make a linear regulator oscillate. ----------------------------EDIT------------------------------------ I change the PNP transitor by a PMOS and I corrected the polarity of the ideal opamp. -...
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2answers
70 views

How can I choose an absolute encoder with appropriate resolution?

I have a motor that runs between 3 to 3000 RPM. The drive update time is 2.2 micro seconds. What is appropriate an encoder resolution for this work (especially for lower speeds) so the drive could ...
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1answer
53 views

Digital control stability for more than impulse response stability?

I have a digital control system which is described by the transfer function $$ Y(z) = \frac{-\beta}{z - 1 + k \beta} X(z) $$ where \$\beta\$ is a real parameter I can adjust to modify the ...
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1answer
49 views

How to find gain and phase crossover from a Nyquist plot?

Note: I need to do this by hand which is why I'm struggling. I'm only using MATLAB here to show the nyquist plot, and I was also using it to try and check my answer. Edit: There are poles at -50, -10 ...
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1answer
93 views

Stability of passive networks

Generally we see that single Port electrical networks (LTI system) that contains resistors and other passive elements are stable . So is it safe to assume that passivity(absorbs power) of electrical ...
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1answer
33 views

Why does op-amp output impedance / parasitic input capacitance pole cause a noise peak?

I was simulating the above circuit in LTspice... I realize the main problem here is the 2MHz peak (which should be fixable with proper compensation), but I'm curious about the smaller 398kHz peak ...
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29 views

Transient and steady state of marginally stable system

I know that if a system is asymptotically stable then after infinite time its output contains only characteristic of input signal and it is also known as steady state and there are no transient ...
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1answer
57 views

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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41 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
65 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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45 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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33 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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21 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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33 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
46 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
63 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
111 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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1answer
39 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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54 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
69 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
49 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
91 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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50 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
121 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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0answers
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
139 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
45 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
56 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
66 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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0answers
77 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
94 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
145 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
45 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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32 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
166 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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25 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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22 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
1k 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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43 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
339 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
407 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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