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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Stability of two-port network
I'm having a hard time understanding what makes a two-port network stable or not. In the paper, Revisiting Llewellyn's absolute stability criterion for bilateral teleoperation systems under non-...
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Fixing Instability in a 5 W Audio Amplifier Board
My prototype 5 W audio amp board based around a (pulled) Rohm BA532 amplifier IC (datasheet) worked just fine. It was built on a section of strip board and was based on the following schematic:
This ...
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Effect of source/input impedance on LDO regulator stability
The datasheet for the MCP1700 family of LDO voltage regulators, in section 5.1 (p.13) states:
...As with all LDO circuits, a relatively low source impedance (10\$\Omega\$) is needed to prevent the ...
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Photodiode circuit to compensate for LED temperature drift
I'm trying to create a stable light source using 5000K white LEDs. In researching this I've discovered that LEDs drift with temperature by a non-negligible amount. Further research leads me to believe ...
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When does the transistor reach the stable status when I add resistor to the emitter
simulate this circuit – Schematic created using CircuitLab
If I add resistor R3, which is an emiter resistor, can it change the value of the base voltage? I've learned that the emmiter voltage ...
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Why do we talk about system stability as a whole when Barkhausen criteria is valid only for one specific frequency?
The relationship AB=1 will be applicable only at a specific frequency. For instance, following is the bode plot for a circuit I have and as can be seen, the barkhausen criterion is met only at 6.3MEG ...
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AC analysis of SMPS shows instability. How to modify the analysis to reflect the transient stability?
Background
I have designed a switch-mode power stage with voltage-mode control that uses an LCLC filter in its output to obtain a very low ripple output voltage.
I have empirically arrived at a ...
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Meaning of long term stability unit (µV/mo)
What does 'mo' stand for in a long term stability spec which has units of μV/mo?
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What is actually meant by stability of a control system in practice?
What is actually meant by stability of a control system in practice? I searched many forums but most of them describe stability in terms of equations and definitions, but they don't describe what ...
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How to determine the phase margin when the Bode plot never crosses 0 dB?
I have a graph that looks like this. I am tasked to measure the phase margin, but the graph doesn't exceed 0 dB.
The circuit is this. The input DC level is 0.6 V, which is the problem. When I change ...
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If the phase margin stability test fails at a very high frequency that I will never reach, is this an acceptable design?
If I have a system that fails a phase margin stability test at a very high frequency that I will never reach, can we conclude that my system is stable, given that we will never reach the frequency at ...
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How to stabilize an op-amp with a MOSFET in the feedback loop
I am modifying a current source/sink and there are three circuits that are relevant which are shown below, all using a MOSFET and an op-amp to stabilize a voltage across a sense resistor. My questions ...
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Stability of driven right leg circuit in ECG amplifier
I am currently writing my Bachelor Project about an ECG amplifier. Common mode voltage on the body has a much higher amplitude than an ECG signal. To attenuate common mode noise a differential ...
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Isolated Converter - Output Y Caps and Output Voltage Relationship
An isolated switching regulator has 680p/250V Y caps from both positive and negative terminals to the earth, for common-mode noise suppression:
simulate this circuit – Schematic created using ...
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Will there ever come a point where you can take the gain margin using the phase at 0 degrees?
I understand that we use the magnitude at -180 degrees since when k increases, the nyquist plot expands and the frequency that will first touch the pole will be the frequency where the phase is -180 ...
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What do the poles and zeros of a system physically represent?
I've been working with transfer functions and control models for a while, but I never really have gotten an intuitive understanding of what the poles and zeros of a system really represent.
I was ...
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DC stability issue with this audio amplifier
This design has a stability issue.
The DC output point (without input signal) should be 0 V with a small offset, but it's not the case, because this point is not stable.
Initially the amplifier had an ...
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CS amplifier feedback stability
I playing with JFET Common Source amplifier with feedback loop. I am simulating the design showed here. https://www.ti.com/lit/an/slpa018/slpa018.pdf?ts=1669662908797&ref_url=https%253A%252F%...
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Negative loop gain of LDO
I am trying to design an LDO with the following specification: Vout = 1.5V; Vin = 1.7V - 2V; Iload = 75uA to 1200uA. However, while I am simulating its loop gain, its gain is coming negative. Even ...
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Stability simulation - breaking the loop for a MOSFET - op-amp current source
The task at hand is to create a voltage controlled current source of 60 mA driving a valve coil (64 mH, 139 Ω). I am aware the MOSFET used is insufficient powerwise; it was a quick attempt to have a ...
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Repeated poles at origin: does this make system unstable, and why?
Let's say we have a control system that ends up having two poles at the origin. I've simulated this and it appears as though this takes the system into instability.
I just wanted to confirm, does ...
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Stability modelling of LT1534
I am working on a high voltage supply (6kV, 100uA) using a Royer current driven oscillator with a transformer and a capacitor multiplier (ratio 6x). The LT1534 switching regulator will be used, see ...
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LDO phase margin
The recommended phase margin to achieve stability is 45. With a positive phase margin, but less than 45, the system is stable, but the output has some oscillation. For LDOs, we have specifications for ...
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Miller's Theorem Application [duplicate]
Miller's Theorem for a capacitor can be written as follows:
In the book 'Design of Analog CMOS Integrated Circuits' by Behzad Razavi, I read the following:
How does the author say that the ...
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Monte-Carlo analysis vs phase-margin or gain-margin
It's my understanding that phase and gain margins are used to see how much margin there is for the stability of a circuit. In other words, how much gain or phase would need to change in order to make ...
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Multistage transimpedance amplifier stability
I am trying to build a transimpedance amplifier consisting of two stages driven by a photodiode with a parasitic capacitance of 11 pF (see below). The GBW of each amplifier is 100 MHz and the target ...
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Are marginally stable systems also BIBO stable?
In the realm of LTI systems (perhaps even in general systems, I am not sure) it is so that if a system is asymptotically stable then it is also BIBO stable. Is that the case when a system is ...
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Op-amp phase margin issue
I have designed a PMOS-based 2-stage op-amp. While performing an AC analysis to check the stability of the design, the gain obtained is high and positive.
The issue I am facing is the phase margin ...
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Instability of op-amp in unity gain configuration
I am using a TSZ121 op-amp with a unity-gain configuration driving 100 pF via 20 Ω at the output. Power supply is 5 V. My input is a slow moving signal between 0.4 and 1 V from a temperature sensor.
I ...
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How is gain margin defined for this control system?
Lets say there is a system
H(s) = 3/s
which I want to control with a controller
G(s) = Kp·(1+10/s)
The Bode diagram of the open loop G(s)H(s) with Kp=1 is:
At the transit frequency the phase is ...
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Effect on stability margins when an integrator is introduced in the loop of a closed loop system
I was asked a question in a control system test which is as follows:
*Introduction of integral action in the forward path of a unity feedback system results in a
a) marginal stability
b) system ...
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Op-amp stable voltage gain out of different input value
Can anyone tell me how to make a circuit with unstable input voltage signal value to a stable output value
For example:
A sinewave in the input between 1 Vrms to 5 Vrms
The output must be a stable 10 ...
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Is this cascoded opamp structure unstable by design (LTspice)?
I am playing with a cascode op-amp design and I have problems judging its stability (schematic at the end of the post).
When I judge the DC or AC analyses, it all looks good. No peaking and good phase ...
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Feedback capacitor vs Miller capacitor in discrete op amp circuits
This is an overly simplified operational amplifier circuit with a feedback applied. The common way to make it stable is to add a dominant pole to the transfer function usually in a form of a Miller ...
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Instability of fully differential op-amp in LTspice
I tested the following circuit including a fully differential op-amp for stability in LTspice. The circuit has an inverting gain of 6 and a roll-off at 4 MHz. When exciting the circuit with a step, ...
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Stability in a double-pole system
A simple low-pass RC circuit is a single pole system and it's stable. In a DC-DC buck converter, we have a conjugate double pole due to the LC filter. Yet, we employ several techniques such as D-CAP ...
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Stability analysis of hybrid discrete-continuous systems
I'm trying to derive the overall state-space system model for a hybrid system, in order to plot its eigenvalues.
The system is shown as follows:
Which is originally from this paper: Modeling and ...
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What happens on a DC-DC grid connection after a perturbation in the synchronous grid?
Consider the Continental Europe synchronous grid. This power system has some DC-DC connections with other countries (for example one with Great-Britain). Suppose now there is a sudden big outage ...
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How are formulas for "in the loop compensation" of capacitive load derived?
I tried to understand https://www.analog.com/media/en/analog-dialogue/volume-38/number-2/articles/techniques-to-avoid-instability-capacitive-loading.pdf
The feedback circuit is as follows:
so I have ...
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Checking calculation of phase and gain margin in LtSpice
I am currently studying DCDC stability analysis in LtSpice. Could you please check my phase margin calculation, am I right? And how about the gain margin calculation? Is it equal to infinity in my ...
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14-Volt 6-Amp Power Supply Stability
Design Requirements:
The purpose is a linear DC power supply for 12-volt aircraft, marine, and amateur radio equipment
power source 20 volts @ +/-10%. (output 85W = 6A*14.2V)
Rser on V1 = 0.4 or ...
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Why are stability circles circles on a Smith chart?
I am new to basic concepts in amplifier stability, so the question might seem obvious, sorry if it is the case.
The amplifier stability translates into the equations for the reflection coefficients ...
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Confused regarding gain margin and stability
I plotted the bode plots of the transfer function:
G(s)= 2.123×10^6 ((0.105s+1.01))/(s^2 (s+12566.37) )
It is as follows:
As can be seen, it shows the gain margin as negative infinity, however loop ...
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Nyquist plot mirrored across imaginary axis
I am reading Foundations of Oscillator Design by Guillermo Gonzales. When an amplifier is connected in a positive feedback configuration, the transfer function is \$A_{vf}(s)=\frac{A_v(s)}{1-\beta (s)...
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On the stability of differentiator based on OP amp with an example from TI manual
I am building a proportional-Differentiator circuit based non-inverting OP-amp. But I am confused with the stability condition of OP-amp.
The system will be unstable if the loop gain |T(s)|=|a(s)B(s)|...
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Stability of dual op-amp Integrator
When we try to analyse the stability of this circuit mentioned here, I find that this circuit is unstable.
It has a zero phase margin. I wanted to know how do we stabilise this circuit for practical ...
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Is the power frequency characteristic of a network almost constant?
When a transient phenomenon happens in an electric power grid, the network reacts to this deviation with a power-frequency characteristic (MW/Hz). Reading the following paper ''Analysis and ...
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Does the feedback capacitor in an inverting integrator appear as a capacitive load to the op-amp in an integrator circuit?
In an answer to a question, I was told that the feedback capacitor appears as a load to the op-amp in an inverting integrator topology. If that is the case, we should see a pole with the output ...
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What is the practical advantage of root locus method in control system engineering? [closed]
Recently I learned about the topic.
Decades ago, when no computational power was available for engineers, it was surely helpful in some way. But I do not understand what the advantage is nowadays, ...
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Stability/damping of AC->DC PSU with DC output Power Line Filter
Application: I am designing a General Purpose 115V 400Hz VAC->28VDC 500W power supply for powering instrumentation aboard research aircraft. Size < 19" x 2U x 6", weight<10 lbs, so ...
