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55
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 ...
11
votes
4answers
10k 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 ...
9
votes
4answers
2k views

Conditional stability

I'm learning about op-amps and feedback and how feedback affects their stability. I've been reading about gain and phase margin and their uses when I came across this: I don't quite understand ...
7
votes
5answers
6k 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) ...
7
votes
3answers
4k 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 ...
6
votes
4answers
2k views

Does this voltage regulator use “on-off” control, or is it a voltage follower?

In Electronics A2 (GCE), we are currently studying voltage regulators. An example voltage regulator circuit is provided using an op-amp and a power MOSFET. I would judge this to be a voltage ...
5
votes
3answers
133 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 ...
5
votes
3answers
4k views

High-stability oscillators (non-crystal)

Are there any high-stability oscilators, which are not crystal based, given that temperature is stable down to 0.01 C and voltage down to 0.001V? Will LC-based oscillator be able to show performance ...
5
votes
3answers
698 views

How to know whether the bandpass filter is stable

I am designing a bandpass filter using MFB. However, I do not know whether my filter is stable or not. Can anyone give me some criteria or methods to evaluate the stability of the filter design?(still ...
5
votes
2answers
603 views

Does MEMS accelerometer stability deteriorate over time?

I am wondering if over time MEMS accelerometer produces any worse output than when it is new? I found this research paper which acknowledges that temperature affect sensor output but there are no ...
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 ...
4
votes
2answers
388 views

Choosing a Tantalum based on Min. ESR - LDO Stability

How does one go about choosing a capacitor for a LDO regulator which specifies a min. ESR? Capacitor datasheets that I've seen only contain the Max. ESR parameter. One could just choose a cap with a ...
4
votes
1answer
559 views

OP07 unity gain

Is an OP07 unity gain stable ? I am powering it with a +/- 5V supply. I am using it to buffer a DC signal which varies slowly. Most of the modern Op-amps have their datasheets mentioning them ...
4
votes
2answers
175 views

Understanding resistors on inputs/outputs of op amps

I was looking at the schematic for Dave Jones' uCurrent, and I can't seem to make sense of why there are 270 ohm resistors on the inputs and outputs of the op amps in his circuit. The resistance is ...
3
votes
2answers
1k views

How can I stablize an analog to digital reading?

I've built a clock out of a PIC16F877, some LEDs and other stuff... To set the time in 5 minute intervals, I'm using a 22K ohm potentiometer connected between GND and +5V with the contact connected ...
3
votes
4answers
683 views

Why is this oscillator unstable?

I designed a simple triangle wave oscillator based around a switchable curent soure. It works for a few cycles, then it becomes unstable and finally stops working altogether. Why is this? If anyone ...
3
votes
3answers
232 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 ...
3
votes
2answers
26k 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
2answers
122 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
1answer
112 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 ...
3
votes
1answer
109 views

Observer Based Control System Design

Consider the discrete-time system described by $$ x(k+1) = \begin{pmatrix}0 & 1 \\ -2 & -3\end{pmatrix}x(k) + \begin{pmatrix}0\\1\end{pmatrix}u(k) $$ a) Find a feedback state vector that ...
3
votes
2answers
112 views

Force amplifier into oscillation

The Minicircuits RAM-8+ amplifier has been replaced by the pin compatible RAM-8A+ part. The old RAM-8+ part was conditionally stable and I had to use an extra output attenuator after the amplifier to ...
2
votes
3answers
110 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 ...
2
votes
3answers
69 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 ...
2
votes
4answers
723 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 ...
2
votes
1answer
701 views

How can you guarantee stability of an inverting opamp configuration amplifier?

I had to design a circuit for measuring the voltage of a negative power supply rail (-15 V) and feeding it into a ADC (0-3 V DC-coupled input range). This measurement is only used for diagnostics and ...
2
votes
3answers
1k views

9V AC stabilizer

I've got a power supply: IN: 220V AC OUT: 9V AC 1A Note that the output is AC, not the conventional DC output. It has no regulation systems built in (simple transformer). I'm looking for a ...
2
votes
2answers
1k views

Op-amps and Capacitive Loads

I understand that having an capacitive load at the output of an op-amp can potentially make the circuit unstable. However, how can I go about calculating this? For instance, I'm trying to design a ...
2
votes
2answers
251 views

Coil-less AC-DC line regulator

I'm trying to fix an AC-DC line regulator that I have build and doesn't work as expected. I'm trying to convert AC 220V mains to DC 5V 10mA without a transformer. To do this I'm using an 1uF 250VAC ...
2
votes
2answers
58 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
259 views

Initial states in a digital system with more than one stable state

Let's say I have a digital system of basic combinational logic with feedback (I do). That is, the value of the gates' inputs depend in some way on the value of their outputs. Depending on the ...
2
votes
1answer
281 views

Given bode plot, determine the poles and zeroes

Ultimately, I want to figure out the transfer function $$H(s)$$ But to know that I would need to know where the poles and zeroes are. Looking at this, I know $$ H(20j) = 0 $$ but that's pretty ...
2
votes
3answers
431 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 ...
2
votes
1answer
75 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 ...
2
votes
3answers
172 views

What is the usefulness of Internal Stability?

In the analysis of a feedback control system is it important that a sub-network be itself stable. i.e. if I were to break apart the main complex system and just study a single feedback loop, is it ...
2
votes
1answer
200 views

Load capacitance estimation for compensation of switching power supplies

I'm calculating a compensation network for power supplies based on the LM20323MH from TI. I have slight doubts about correct estimation of output capacitance to use in the calculation. The board is ...
2
votes
1answer
5k views

Arduino alternate PWM input method

I'm working on a rudimentary flight stabilization system for an airplane, which reads in 4 PWM inputs from an R/C receiver. The problem is, the pulseIn command is taking far too long to execute, so I ...
1
vote
1answer
35 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 ...
1
vote
2answers
351 views

What happened when P controller's gain equal zero?

For example, I use Routh-Hurwitz Cirterion to examine the following system with P controller gain K: \$\frac{{K\left( {2 - s} \right)}}{{{s^3} + 3{s^2} + 5s + 3}}\$ I closed loop it with H=1 and ...
1
vote
1answer
68 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 ...
1
vote
1answer
2k views

Where to find derivation of s'' (stability factor for beta) for BJTs?

I'm looking for the derivation of the formula for the stability factor (\$S''\$ or \$S(\beta)\$) of BJT bias circuits, particularly the ones with emitter resistance. The book I'm using says that the ...
1
vote
4answers
1k views

Powering 28 LEDs in series by 220VAC - simple stabilizer

I have a home-made thingy that I would like to use as a lightning in my living room. It contains 7*4=28 LEDs (red, 1.86V, ...
1
vote
1answer
66 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, ...
1
vote
1answer
51 views

State Feedback Controller

Are there any values of \$\alpha\$ for which it is possible to find a state-feedback gain for the system by bringing all closed-loop poles to zero? If your answer is affirmative, find a feedback ...
1
vote
0answers
77 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 ...
1
vote
0answers
169 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. ...
1
vote
0answers
122 views

Forming Nyquist Plot from magnitude and phase transfer function graphs?

So the solution is present above, but I'm having issues understanding the Nyquist Plot. So here's what I know from the magnitude and phase graphs: At \$\omega = 0\$, \$G = |\infty|\$ At \$\omega ...
0
votes
3answers
191 views

Securing a pcb to be used in a keyboard to its case

I'm looking for a way to secure a pcb I will be making for a cherry mx (homemade) keyboard to a case which I'll also be making. Obviously, I don't want the pcb to move. I could use standoffs/screws, ...
0
votes
2answers
399 views

Vanilla crystals stability

I wonder which of commonly used crystals in PC have higher short- and long-term stability, in stable temperature & voltage environment? Crystals I commonly see there are: 32kHz watch crystals ...
0
votes
2answers
105 views

Phase Margin Criterion

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