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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What frequency stability crystal do we need?

We're designing a simple digital clock and using a 32.768 kHz crystal with a frequency stability of 20 ppm (standard off-the-shelf SMT). We're finding the clock is running fast by about 2.5 minutes ...
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60 views

Instabilities in constant current sources at low load impedances

I want to turn my constant voltage source into a constant current, voltage controlled. For this, I used the following circuit. If the ERV error signal is connected to the UCT, the assembly functions ...
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LDO Outputs wrong voltage

I am working with a very low profile LDO, TCR5RG18A and I'm having issues at the regulators output. It's outputting 0.9V which is half its nominated value (nominal value = 1.8V) The LDO is operated at ...
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65 views

How to measure the stability of sine wave peak-to-peak voltage

I am currently using AD9833 to output a sine wave signal. I have seen the sine wave signal on oscilloscope and saved a CSV file on my flash drive. I plan on using an Excel or Matlab to determine the ...
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229 views

BIBO and impulsive stability in voltage-controlled electrical circuits

Branching from the comments here, TimWescott gave this example of an open-loop unstable electrical system: Find the nearest NPN power transistor. Put it in a circuit with a healthy (for it) voltage ...
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148 views

Open loop system instability

I'm studying system stability, and I know a closed loop system can be unstable due to the feedback. I also know that an open system can be BIBO unstable (e.g., a capacitor with a direct current input)....
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1answer
46 views

Flyback bode plot & type 2 comp

I'm trying to compensate a flyback boost circuit. Unfortunately I seem to be failing to make the gain of the system ever cross 0 dB. I feel like I'm missing something obvious... Like a pole? I'm ...
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4answers
226 views

Why is this integrator unstable?

I am trying to convert an acceleration signal to a velocity signal using an integrator. After building the circuit, it turned out to be unstable: With no signal at the input (...
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1answer
91 views

Is the 'UniversalOpamp2' in LTspice useful for stability in capacitive drive applications?

When using a level 2 UniversalOpamp in a unity gain capacitive drive follower application, I find that it is quite stable. I decided to compare the results to an actual opamp model of the LM7321. I ...
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78 views

What is the better way to stabilize this discrete op-amp and why?

I have the following simple op-amp circuit, which is meant to drive a MOSFET (M1) gate and work as a voltage regulator. It is discrete for a mix of reasons (necessary bandwidth, using existing BOM ...
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BIBO stability on a accumulator system from oppenheimer book

Is this stability correct?. If im getting it right, x[k] has a bounded value(M), so the interval between the summatory times this value tells the max value of output. But shouldn't it be |n - no + 1|M?...
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How to set up an LTSPICE test bench for Common Mode Feedback Loop Stability

Suppose we are given a fully differential (low voltage single supply) op amp with common mode feedback. It is common knowledge to break the loop in order to measure open loop ac performance for loop ...
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Why is my voltage pulsing when using a DAC as an input to an OTA?

I'm using the LM13700 in an automatic gain control configuration to adjust the volume of a speaker based on the audio level perceived by the microphone. Both amplifiers on the chip are used: one to ...
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Ideal OpAmp differentiator stability

So, for OpAmp stability, we don't want \$A_{OL}\beta\$ to be -1, which we can derive from the Bode plot by looking at: \$20\log(A_{OL})-20\log(1/\beta)\$ and looking at the rate of closure to indicate ...
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Disadvantage of 3rd order vs 2nd order digital PLL with high C/N0?

I tried to determine the best choice between an aided 2nd order and an unaided 3rd order carrier digital PLL in a context where the \$C/N_0\$ is very high. From all aspects, the 3rd order loop seems ...
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3answers
201 views

Problem stabilizing this PMOS LDO

I am considering a discrete LDO for a supply rail that needs ~\$m\Omega\$ impedance at 10 kHz. While the following circuit does what I need (according to Spice), it becomes unstable if C2 is smaller ...
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95 views

Why does Nyquist plot show no encirclement when positive feedback is unstable?

Amended the previous question to be more concise I have the following open-loop plant: $$G(s)=\frac{21.95s^2+224.2s+1906}{s^4+32.7s^3+285.8s^2}$$ These are the poles of the plant, and as you can see, ...
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1answer
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Flyback power supply instability issue

I have created a switching power supply: Input: 230 V AC Output: 12 V DC, 1 A Controller: UC3844 Topology: flyback Switching frequency: ~ 100 kHz Schematic: When I start this power supply, output ...
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2answers
83 views

What happen if one connects two live phases together? [closed]

If a house is running on 1 phase wire and is flipping instantly or not stable for a short period as it drops from 200v to 170v and return back to 200v in 10 seconds. Would connecting another phase to ...
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110 views

Why does the rotor magnetic field lag the rotor current by 90° in a 3 phase induction motor?

I was trying to understand load angle in electrical machines, generally denoted by delta, and I found out that while delta needs to be less than 90° in synchronous machine for steady state stability, ...
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0answers
54 views

IGBT Temperature Drift: How to Achive Stability?

I remember the BJT transistor circuits are designed to compensate for the fact that the parameters of the transistor change with the temperature. I could not find similar ready-to-use solutions for ...
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98 views

Why does this oscillator not work with a voltage less than 9 V?

By chance of my research and simulations and various tests, I found the diagram of an oscillator with strange behavior. All the oscillators (quasi) that I have encountered work whatever the supply ...
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Why does this PMOS LDO require no compensation to be stable?

LDOs with PMOS pass transistors are prone to oscillation due to positive feedback problems as discussed e.g. here. Now the below simple circuit is basically a PMOS LDO, but seems stable in both time ...
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1answer
81 views

Please help me clear up this confusion regarding gain margin and phase margin and unity feedback

I understand the physical significance of gain and phase margin. However, I would like some clarification regarding the mathematical aspects. Videos such as the following: https://www.youtube.com/...
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118 views

Voltage regulator stability, PMOS v NMOS pass transistor

Currently, I am considering some LDO replacement circuits because some parts have bad availability. For small current demands (up to maybe 20 mA) I think, a simple opamp will do fine, but for larger ...
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1answer
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Stability problem when using an OpAmp to drive a BJT for high current application

I am designing a circuit for my lab, and in that application I need to have several low noise current source driving coils at roughly 7V, 20A. I could not find a benchtop power supply cheap enough so ...
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35 views

Phase lower than -180 when reaching unity gain, is it unstable or can we substract 360?

I am getting a phase of -434 degrees when reaching unity gain (0 dB point). The phase curve starts at 0 degrees, thus, can we consider that -434= -434+360= -74 degrees and the phase margin is of 180-...
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Caveats of the RC phase shift oscillator

I was reading some articles online where it talked about this kind of RC oscillator. I just want to clarify some caveats about this circuit: From: https://learnabout-electronics.org/Oscillators/osc31....
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3answers
322 views

Understanding on frequency compensation on driving capacitive loads with an op-amp

I am trying to understand an example circuit of frequency compensation on driving capacitive loads with an op-amp from: https://www.allaboutcircuits.com/technical-articles/how-to-drive-large-...
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2answers
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Reduce hard voltage drops on mains? [closed]

I'm experiencing some hard voltage drops on my AC power line (measured at 20 points across the house). The culprits are the washing machine and dryer (as well as our upstairs neighbors washer and ...
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38 views

Are there common circuit stability issues at low current levels and/or recommended minimum values?

I'm building a small semi-permanent solderable PCB circuit using a couple of mosfet inverters, plus some resistors for voltage division and pulling inputs/outputs high/low. The final location will be ...
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1answer
80 views

LDO minimum current requirement

Is it good practice to use resistors (parallel to load) on LDO output? The MIC29302WU LDO I've bought has ~7 mA minimum current requirement for stability reasons. What other/better options I have? (...
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2answers
77 views

Will adding a pole in the loop gain make the system more unstable?

In the design above, the circuit designer added a low-pass filter in the feedback path of the op-amp for loop stability. Won't adding a pole to the feedback factor actually make the circuit more ...
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1answer
102 views

Bode plot starting from 180?

This is an NMOS common source amplifier and I'm trying to calculate the Phase Margin, but it's starting from 180 instead of zero? dose it mean I have poles at the origin or it's very stable?
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Nyquist plot - is my system stable?

I am working on a balance controller for a robot. I have obtained a transfer function between the robots motor voltage and the robot pitch angle. $$G= \frac{ -5.893e05 s^4 - 7.71e08 s^3 - 1.435e11 s^2 ...
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1answer
89 views

Measuring Allan Variance

I have some microcontrollers with TCXO's where I wish to measure their frequency stability using Allan variance (from say 1ms to 10s). However, my measurement equipment is limited. I have access to a ...
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1answer
44 views

How to guarantee the stability of a RF closed loop amplifier with inner loops?

I've a 3 stage closed loop amplifier with many loops inside of which some loops cannot be broken, to analyze the loop gain, as the parasitic capacitors are intrinsic to the device. What is the method ...
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1answer
82 views

Real/Complex Zeros for Filter Transfer Function

So I've been reading into filter design and came across how to determine the transfer function of a filter, when given it's poles and zeroes. I've come across the following question that has me a bit ...
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1answer
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Analyzing effects of sixth order transfer function

This question is in relation to this question asked before (Settling time of sixth order denominator transfer function), but formulated in greater details. So I have a transfer function which looks as ...
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255 views

unstable systems with positive phase/gain margin

Open loop Phase/Gain margins provide information on how much margin the closed loop system have until it becomes unstable. In other words, how much you can increase the effective loop gain and or ...
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2answers
68 views

Modeling MOSFET Pole and Transconductance for use in Larger Overall Control System

Recently I began a project involving some active current limiting using a MOSFET and an Op Amp. It is part of a larger overall circuit involving other Amplifiers. I would like to perform a block-...
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0answers
31 views

Stability of circuit with amplifier with filter and impedance matching on input and output

I recently asked a question about an amplifier with impedance matching at the input and output of the circuit. Now that I know the matching is greater, I wanted to generate a Smith chart regarding the ...
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4answers
111 views

Why are identical value vs different value capacitors between positive and negative voltage supply leads?

I understand why various different value capacitor are added in low voltage power supplies....to be able to respond and absorb various size/frequency spikes. But why are there also identical value ...
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How does this compensation network work?

By accident I stumbled upon this Linear Technology application note (LT1074/LT1076 Design Manual): https://www.analog.com/media/en/technical-documentation/application-notes/an44fa.pdf Just for fun I ...
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2answers
205 views

Closed loop system stability with Bode

Stability of the closed loop system (with -1 feedback) can be assessed via Bode plot gain/phase margin analysis of its open loop system. How can one deduce stability of the closed loop system directly ...
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1answer
86 views

Why is the slope of the op amp graph 20 log (AB) in this application note

I am going through the following guide for op amps : http://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf On page 87 (screenshot attached) there is a bode plot which has got me slightly ...
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1answer
79 views

HSPICE create a voltage source in top level and instantiate it in a .subckt

I am fairly new to HSPICE and I am investigating someone else's testbench and I am trying to track down where is the vsource generator used in the .lstb analysis in this testbench. I am a bit ...
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2answers
70 views

Does a Lyapunov Function derivative necessarily vanish at each equilibrium point of the system?

From Jean-Jacques E Slotine's book "APPLIED NONLINEAR CONTROL" "several Lyapunov functions may exist for a given system, and therefore several associated invariant sets may be derived. ...
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1answer
112 views

How to prove a system is stable if the characteristic equation have non zero positive coefficients?

I read that a control system would be stable if its characteristic equation has got all the terms present and are positive. But I could not find any proof to it. How does one prove it?
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331 views

20 dB/Decade - Justification

I've read that it is recommended to have 20 dB/Decade slope on the L(jw) magnitude plot of the Bode Diagram at gain crossover. This seems to imply a slope of -1 in dimensionless terms. However, what ...

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