# Questions tagged [stability]

The ability of an electrical circuit to stop oscillating within a finite period of time. Related topics include the Nyquist stability criterion (and the associated Nyquist plot), Bode plots, and gain and phase margin.

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### 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 ...
1 vote
609 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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1 vote
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### 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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1 vote
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### 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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### Is a type-2 system always unstable?

If there are multiple poles at the origin, a system is unstable. A type-2 system will be have $s^2$ in the denominator. So it should be unstable, right?
1 vote
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### 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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### 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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1 vote
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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### 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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### Transimpedance amplifier calculating feedback capacitor

What is the correct way to calculate $C_F$ of the transimpedance amplifier? Since I have seen two different documents, and each has a different way to calculate it. These two documents are: Akshay ...
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331 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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### 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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944 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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748 views

### Opamp stability given in not inverting configuration

If a datasheet (like AD828) says that an opamp is stable at Gain >2 (or reccomends to work with G>2, hence it is clearly not unity gain stable), what can we deduct about its stability in the inverting ...
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1 vote
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### Stability Current Sink

I’m currently trying to create a programmable current sink. And I’m still trying to build up my circuit and searching for new parts. As I was searching for a OPA, I encountered much information about ...
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### Effect of RHP zeros on stability

Why do zeros in the right half of the $s$ plane reduce stability (i.e., gain / phase margin)?
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### Stabilize circuit on 5V 2A

I have not yet build following circuit: Circuit in high performance needs 5V 1.7A (measured). I have source which is powerbank with 16 000 mAh. Outputting via ports: USB-C 5V/3A, USB-A 5V/3A, Micro-...
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### Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

I built a prototype keyboard/sound synthesizer using a chain of 13 astable multivibrator circuits whose outputs are connected to an audio amplifier chip (LM386) and speaker, all powered off a 9V DC ...
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### Stability Criteria of Type 3 Digital PLL

I suppose we can derive the stability criteria based on poles of open-loop transfer function of F(z) in expression (4.11). However, the pole analysis does not help in deriving the stability criteria ...
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### Is this mosfet stable? Trouble with capacitances

I have the following circuit and I'd like to know about its stability : From what I've learned from basic electronics courses, the first step is to add the parasitic capacitances. I know there is one ...
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### Questions about stability circle and impedance matching

I'm a RF circuit beginner and got stuck in stability related issues. According to Pozar's textbook, output stability circle is a contour in the "gamma_L" plane and its arc represents the "gamma_L" ...
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### Does the stability of an LTI system depend on the input?

Consider a system $G(s) = \frac{1}{s}$. It is marginally stable, as it has its only pole at $s=0$. However, if we apply a step input, the output is $tu(t)$, which turns out to be unstable. ...
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### Stability at loop gain <1 and 180 degree phase shift

I'm reading this article about stability of OpAmps: Link to article. It says: "If Aβ is less than unity at the high frequencies where phase shift reaches 180°, the high-frequency phase-shifted ...
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### According to the Nyquist criterion this system is stable but when I apply an impulse I get an unstable response, why?

I have this open loop transfer function and I have to study the stability of the closed loop transfer function using the Nyquist criterion. What I got is that the characteristic equation 1+GH(s)=0 has ...
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### Series voltage reference unstable with a series resistor

I am using the MAX6035 as a 5V reference that draws 5mA load current. To protect the input from transient spikes, I thought a simple resistor and zener diode circuit would work well. I noticed that ...
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### Nyquist Stability Criteria

Find the stability where: Find the stability: $G(s)= \frac{(s+3)(s+5)}{(s-2)(s-4)};$ $H(s)= 1;$ I run this code in matlab: ...
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### How does transistor bandwidth affect stability?

I was watching a video where Dave Jones of EEVBlog interviews Rod Elliot of Elliot Sound Products. Rod was discussing that he tends not to use digital chips in his designs because the chip will become ...
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### induction motor stability

Does the change in slip (s) have any impact on load torque in an induction machine/motor? I know it affects the motoring torque. But do the load torque also get affected by the slightest measures if ...
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### Derivation of stability criterion for type 3 digital PLL

Could anyone help to derive the following expression (4.23) which is the stability criterion for type 3 digital PLL ? Note: Screenshots are taken from Floyd Gardner's book : Phaselock Techniques 3rd ...
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### Cap maximum wall outlet voltage

I live in a rural area. A problem occured when my UPS could not run my computer simply because of voltage fluctuations. I have tried many stabilizers but its too rapid that it would make a tick and ...
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### Determine the value of a constant for which the system is marginally stable

So I have the following transfer function $$G(s)=\frac{s^2+0.1s}{10s^3 + 1.1s^2 + 0.01s + 2K}$$ Now I'm trying to determine the value of K so that I have a marginally stable system. I'm not supposed ...
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### Non-inverting op-amp configuration with capacitor

I don't really get what is the purpose of the capacitor C1 which is connected in parallel with the feedback resistor. After my knowledge, if we modify the input signal frequency the over all gain will ...
1 vote
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### LT spice not predicting instability

I'm trying to make a linear regulator using an op amp and a pass transistor. Here is the circuit: From my limited understanding you can predict the stability of the circuit's feedback loop by ...
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### Op amp driving a LED oscillates, how to stabilize?

I have a simple LED driver circuit like this: simulate this circuit – Schematic created using CircuitLab The op-amp is OPA354 250-MHz, Rail-to-Rail I/O, CMOS Operational Amplifier supplied ...
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### Compact thermostat for VCO temperature stability

So I have a voltage controlled oscillator with an exponential input made using the THAT2181 VCA IC. The schematic is shown below - the THAT2181 IC is used to change the C4 capacitor charging current ...
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### Meaning of the "pole" of a transfer function with time delay

I learned in basic control theory that we can determine the stability of an LTI system by the signs of the real part of the poles of its transfer function $H(s)=\frac{N(s)}{D(s)}$. For a rational ...
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