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12
votes
4answers
15k views

Choosing resistor values for non-inverting amplifier and why?

The gain here is A = -Rf/Rin. However, lets say I want a gain of 10 V/V. Which resistor value would you choose and why? I know that you could have infinite number of combinations for these ...
0
votes
2answers
39 views

How do I calculate phase margin for a feedback amplifier

I'm learning analog design and can't seem to get a firm grasp on the concept of phase margin and wanted to ask a few questons: First Part: I understand that Phase margin is the difference between ...
0
votes
0answers
51 views

Nyquist criterion and the gain/phase margin of transfer function?

Now to determine gain/phase margin I need the bode plot. and to find the value of k such that the system is stable I have to do Nyquist criterion for the closed loop transfer function. (Question: ...
0
votes
0answers
27 views

How to determine the stability from Nyquist plot for Minimum and Non-Minimum Phase system?

For a non-minimum phase system there are some zeros that are in the RHP of S_plane and since the Nyquist plot Does't encircle the origin there Must #of pole in the RHP that equal to # of zeros In ...
0
votes
0answers
66 views

Failing to stabilize voltage

I need advice on stabilizing a voltage source. I've read some articles and threads on this, but with voltage stabilization the solution seems to vary very widely depending on the concrete problem. I ...
1
vote
3answers
83 views

Delay and Stablity in Negative Feedback Systems: Confusion-2

This question is in reference to my earlier question: Delay and Stablity in Negative Feedback Systems: Confusion In that question I wanted to ask why the second order system is always stable. But I ...
3
votes
2answers
102 views

Delay and Stablity in Negative Feedback Systems: Confusion

Below is a block diagram that shows an op-amp in negative feedback with feedback network made from resistive divider: The encircled block is Op-Amp with 1 and 2 as its inverting and non-inverting ...
1
vote
1answer
34 views

Amplifier with two-pole is unconditionally stable

This is from a lecture slide: Amplifier with a single-pole is unconditionally stable. Amplifier with two-pole is also unconditionally stable. Are these properties considered for ...
3
votes
3answers
92 views

Phase margin analysis of a [diy] PMOS LDO [with LTspice]

I'm somewhat familiar with using LTspice to do phase margin analysis for a classic i.e. obvious negative feedback path opamp circuit; in fact I've done that analysis successfully for fixing real opamp ...
10
votes
6answers
8k views

Stability problem in unity-gain opAmp

As a part of a controlled power supply for hardware-in-loop testing for a student driven project, I had to develop a current buffer (voltage follower) which could source up to 1 A. I had the (bad) ...
0
votes
0answers
44 views

Modeling a feedback loop in spice

I'm having some difficulty with an asymmetric half bridge design. I've never been great with control loop theory, and I'm wondering what the best way to figure out the R and C values for the feedback ...
0
votes
5answers
409 views

Using more than one voltage regulator in series

Is there any problem (in addition to a likely loss of current) in using more than one voltage regulator (L7812CV) in series? And is there a real gain in stability? I ask this because I 'm going to ...
3
votes
2answers
97 views

Systems stability with zero poles

I have a rather simple question I would say. I know that systems having real poles to the right side of the plane will inevitably be instable (for LTI systems at least). But I'm confused with ...
2
votes
1answer
145 views

Unstable points in a basic memoryless circuit

I have been told that there can be more than a single solution to a circuit, and that some of those solutions might be unstable. As a simple example, a resistor with a constant power source, connected ...
0
votes
1answer
57 views

Step response of feedback system

We have a feedback system F(s) as in this figure: and this is the step response of G(s): and H=10. F(s): We got the root locus of the system F(s) as this: then we determined the gain ...
3
votes
4answers
1k views

Is it ok to clip component leads after soldering?

When working with through the hole components, I have read that you should clip leads before soldering so the shock from clipping doesn't break the joint. On the other hand I've seen a ton of ...
3
votes
3answers
411 views

Can there be “too much” capacitance on a buck regulator output?

I've an MPM3610 buck regulator module with an integrated inductor of 0.47 µH and a fixed internal compensation. It employs constant-on-time regulation. The datasheet gives some application ...
0
votes
0answers
61 views

Stabilize Vds with a clean voltage reference

I suppose we can simply stabilize V_ds using a voltage reference, like a zener diode (a very clean signal one) to stabilize a MOSFET and keep it from swinging it's Vds and therefore the Id and ...
0
votes
1answer
50 views

Stabilize a 12V DC supply (from Lipo)

I'm newbie in electronics, but I want to learn some basics things. I have a 12V DC output (from a charging/discharging PCB Lipo battery), and I would like to stabilize it to run a mini-amplifier ...
3
votes
2answers
148 views

Why do we take gain and phase margin from these points in stability?

In the following graph, why do we take the phase margin from -180 degrees and the gain margin from 0 dB in stability?
0
votes
2answers
68 views

Control: what is the proper justification that you can't just make the output equal to the input if the system produces unstable output

Suppose we have a signal, it goes into the plant and generates an unstable response, a common question then arise at that point is why can't we just set our output to a "hard-coded" input. Think of ...
13
votes
2answers
586 views

Why are low-dropout (LDO) voltage regulators unstable?

LDO regulators based on P-type transistors seem to be the preferred form of linear voltage regulator today, but I keep hearing about how I have to choose the output capacitor(s) carefully to guarantee ...
1
vote
1answer
35 views

Explanation for stability criterium microwave amplifiers

Given a general microwave amplifier circuit For this amplifier (transistor) to be stable the the magnitude of the input and output reflection coefficient must be smaller than 1. But why? What is ...
6
votes
4answers
3k views

Gain margin and Phase Margin Physical Meaning

I have been trying to understand the physical concept of Gain and Phase Margin.From what I understand it a relative comparison around the critical point (-1,0) which when converted to magnitude and ...
1
vote
1answer
44 views

phase-stability two op-amps

I'm trying to simulate two op-amps back-to-back (G=30 each) in LTSpice and work out if they will be stable. If I look at the .ac analysis after the fist op-amp I have good phase margin (about 60 ...
0
votes
0answers
46 views

How to choose output network RC and RL values of an audio amplifier?

With "output network" I'm referring to that RC series circuit connected from the amplifier output to the ground, and the following RL parallel circuit connected in series with the output. I know what ...
0
votes
2answers
325 views

Phase Margin Criterion

Why is 45 degrees considered minimum phase margin. Is it just for stability considerations or some other reasons too? Thanks.
3
votes
3answers
195 views

Why 60% overshoot with 55° phase margin?

UPDATE: Based on the answers I received, I got this working beautifully. There's a full outcome report in one of the answers below. I'm working through the design of an electronic load, basically a ...
1
vote
1answer
79 views

Why does smaller step show instability better?

I was stability testing a simple op amp circuit by applying a square wave to the input and looking for ringing etc. on the transitions. I figured, hey, I'll give it a big whack, say from 0 to 5V, ...
2
votes
3answers
83 views

How do I determine \$R_o\$ for an op amp?

I understand that when driving a capacitive load with an op amp, the output resistance, \$R_o\$, of the op amp interacts with the load capacitor to form a low-pass filter, introducing a pole in the ...
0
votes
0answers
78 views

Is it possible to describe an unstable circuit in VHDL?

i was reading this (VHDL: Signal assignment question) post and i got curious about an issue that i wander if it could arise writing VHDL code. Is it possible to write the code for an unstable ...
2
votes
2answers
83 views

What can be inferred from the frequency an op-amp is oscillating at?

For whatever reason, I seem to create a lot of oscillators in the course of developing circuits involving op-amps. I'm wondering if the frequency of oscillation, which normally appears to be quite ...
2
votes
3answers
496 views

What does it mean for amplifiers to be stable only down to N gain, where N > unity?

This is related to What's special about "unity-gain stable"? which is about unity gain stability. But what exactly does it mean if some op-amp is said to be only stable to, say, gain ...
56
votes
7answers
4k views

Why is my circuit so incredibly sensitive to electric fluctuation?

I recently finished building a circuit showcased in a beginner’s electronics book. I have included the picture of my creation below because I think it may become relevant to the question. At the ...
1
vote
1answer
93 views

Step-down converter and ceramic minimum ESR capacitor

I'm building a step-down converter, based on the TI TPS5450, which provides a reference design and various considerations on the capacitor. Even on the minimum ESR required. But when states "The ...
3
votes
2answers
296 views

Alternative ways to maintain temperature stability of silicon BJT circuits other than feedback resistors

So I've been messing with Bipolar Junction transistors lately and I'm trying to really nail the concepts of designing circuits with these things cause I want to start using them in some of my circuits ...
3
votes
3answers
649 views

Why is my op-amp oscillating?

I am attempting to build the following circuit using an LM6171 op-amp. I know that this op-amp is unity-gain stable. I previously had this circuit working with an LT1637 op-amp, but I had to switch ...
7
votes
3answers
6k views

Converting and Stabilizing output voltage of a dynamo hub

Preface - I don't know much about electronics :P I have ordered a Shimano dynamo hub for my bicycle. I have done a little homework and here are my findings about it: The output of the above ...
0
votes
2answers
497 views

Obtaining stability information from Bode plots

I am trying to understand the theory behind gain and phase margins from Bode Plots for systems with negative feedback, specifically this one: The transfer function for this system is: $$ ...
4
votes
5answers
1k views

What components or circuitry exist that can provide extremely high speed, accurate clocks?

I've been curious for awhile now about doing some high speed projects, such as measuring time differences of radio wave reception, and was wondering if there exists components that provide clocks much ...
-1
votes
2answers
49 views

Feedback Stability Comparison [closed]

Compare the Feedback conditions given below in terms of stability:- Negative Feedback Positive Feedback with LoopGain < 1 Positive Feedback with LoopGain = 1 Positive Feedback with LoopGain > 1 ...
2
votes
1answer
91 views

AP5002 step-down switching regulator loop stability

Problem, parameters I have an 5V output power supply, with 2S LiPo input (6-8.4V), implemented with AP5002 (PWM control 2A step-down switching regulator, docsheet), and for the life of me, I can't ...
0
votes
2answers
115 views

Why would the Schmitt trigger relaxation oscillator a bit unstable?

This thing oscillates from time to time. Why? (Respect part numbers, all chips from NXP) simulate this circuit – Schematic created using CircuitLab ...
0
votes
3answers
61 views

What things to think about when selecting a relay for controlling small valves?

We are creating a novelty drink dispenser that controls a set of 8 pumps with a Siemens Simatic Step7 1200 PLC. The decision to use this PLC was based on our need to have a very stable prototype. Now ...
3
votes
2answers
35k views

How to determine a system is stable using pole zero analysis?

To my knowledge, as long as the poles of the transfer function are in the left half plane, then the system is stable. It is because the time response can be written as "a*exp(-b*t)" where 'a' and 'b' ...
3
votes
1answer
172 views

Effect of zeroes in system stability

Suppose we have two third order systems (a and b), with three poles and two zeroes,poles for both the systems are at the same positions in frequency domain but these systems differ in the placement of ...
1
vote
0answers
99 views

Self-oscillation in a commercial RF amplifier

I purchased several 50 ohm (in/out), 35 dB gain photomultiplier tube (PMT) amplifiers from a vendor assuming I could use them to read out the voltages on my PMTs. The amplifiers are AC coupled with a ...
2
votes
4answers
1k views

Stability and loop gain of negative feedback systems

When we look for stability of a feedback system, why do we only concentrate where loop gain is unity and check the phase margin there. The phase of the closed loop system might be passing through 180 ...
0
votes
1answer
80 views

Powering circuit with alternative and/or concurrent power sources

I have one of these led projectors which is normally powered by the embedded motion sensor. I want to be able to power it manually by a switch button. I need to do this in both alternative and ...
1
vote
0answers
204 views

LDO Regulator Overshoot

I'm using an LP38691 3.3V fixed regulator which is overshooting. This wasn't an issue for years, but now a component is being replaced and the current on the 3.3V rail has gone up from 300mA to 500mA. ...