58 votes
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Why is my circuit so incredibly sensitive to electric fluctuation?

The advised capacitor is a long-lead buffer, so to speak. Even if you had a perfect power supply, the cables that run to your design are far from perfect. And that's not your fault, it's just how ...
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39 votes

Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

You have clearly built a circuit that is fully analog in nature and produces a frequency in each oscillator that is dependent upon various factors such as: Changes to the voltage level of the power ...
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33 votes
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Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

What I can't figure out is why the circuit appears to get spontaneously detuned, i.e. one or more of the individual circuits end up with frequencies that are different from what they were tuned to (...
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30 votes

Gain margin and Phase Margin Physical Meaning

Gain and phase margin are usually applied to systems that are amplifiers of some sort with negative feedback around them. The more negative feedback, the tighter the system is controlled. However, ...
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20 votes
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Stability of input filter in SMPS - Theoretical explanation

It is an extremely complicated subject. I have taught an APEC seminar in 2017 and tried to explain the interaction between a filter and a switching converter. First, you need to understand that a ...
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18 votes
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Why are low-dropout (LDO) voltage regulators unstable?

A LDO is a control loop. And like all control loops, there is always room for instability. So how do you make a control loop stable ? You provide sufficient phase margin (difference in phase from ...
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17 votes

What frequency stability crystal do we need?

Too long to read all that stuff so, here's the short story From comments under the question, Trevor says this: - we think the caps are correct. We have 2x 15pf to ground. The crystal we're using is ...
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15 votes

Why is my circuit so incredibly sensitive to electric fluctuation?

The combination of solderless breadboards and long wires is deadly, especially when you get to any complexity. Try this as an experiment: replace all your ground and power wires with jumpers which are ...
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15 votes
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What is noise gain, really? And how is it determined in the general case?

Okay, after a lot more research, I think I've gotten to the bottom of this. Actually I'm certain it's only approaching the bottom, as I've found this topic area quite deep, but I think I've gotten ...
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15 votes

What frequency stability crystal do we need?

If you have a suitable means of measuring the frequency, you can adjust one of the load caps with a trimcap to get closer to the ideal. However you will need some means of measuring without altering ...
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14 votes

Why is my circuit so incredibly sensitive to electric fluctuation?

Breadboards have parasitic capacitors (in the order of pF) and inductors (in the order of nH) that can form oscillators with your active components. Since these parasitics are quite small, the ...
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14 votes
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Where do the oscillations on the output voltage of my buck converter come from?

Repeat your measurements but this time connect your probe tip to the same point as your earth clip. What do you see? If your probe is picking up a signal directly due to the inductive loop it forms ...
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12 votes
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What components or circuitry exist that can provide extremely high speed, accurate clocks?

I've been curious for awhile now ... and was wondering if there exists components that provide clocks much faster than a typical CPU can, such as up to 10 GHz or higher. Opto-electronic Oscillators (...
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10 votes

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

"The older high-dropout regulators with N-type transistors didn't seem to have this problem. " The answer is as follows: The npn-type transistor used as a control element is operated in a common-...
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10 votes
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Is it ok to clip component leads after soldering?

I was told to cut the leads to length before soldering. There was an IPC standard around on which basis we were taught that. I don't remember which standard it was exactly. A reference I found is ...
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10 votes

Why does music synthesizer built from chain of astable multivibrator circuits get "out-of-tune" after a few hours?

Yet another factor which has not been mentioned is the fact that the circuit is battery-powered. Since you are driving a speaker, power consumption will be significant (as evidenced by your use of an ...
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9 votes

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

If you want to suppress the ripple more, you can add more output capacitance BUT don't place it directly in parallel with the 10uF output capacitor. Instead, make an LC filter so first through an ...
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9 votes

Can a 7805 ever oscillate?

It's quite challenging to make them misbehave to the point of oscillation in practice, especially with light loads. Try heavy loading, no input capacitance at all and some source inductance, but I ...
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9 votes

Feedback loop-gain(beta) derivation for the inverting amplifier?

Definition: The feedback factor beta is defined as the portion of the output voltage that is fed back to the differential opamp input (input source grounded). Therefore, regarding beta there is no ...
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9 votes
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Understanding in-loop compensation for capacitive-loaded OpAmp

I believe the authors used fast analytical circuits techniques or FACTs but I am not sure about their results. The principle is based on the generalized Extra-Element Theorem or EET from Dr. ...
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9 votes
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Capacitor of choice for low noise applications

HighK ceramics like X7R, Z5U etc have huge variation of capacitance versus voltage. Using them in filters or any kind of coupling application guarantees humongous distortion. They are piezoelectric: ...
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9 votes
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Capacitor after Voltage Reference "for stability"

The reference has a low dropout, so as you can see on the internal schematic (datasheet page 10) it is implemented as a bandgap reference followed by a rail to rail buffer opamp. Notice the polarity ...
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9 votes
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Non-inverting op-amp configuration with capacitor

A lot of times I hear that it's useful for stability but I don't get why and how to calculate it's value. Consider that the non-inverting pin might have a parasitic capacitance of maybe 4 pF. That'...
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8 votes
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Why 60% overshoot with 55° phase margin?

I would go with Hypothesis 2. I think, you have simulated the loop gain correctly. The input impedance at the inv. input seems to be much larger than the combined source impedance of the remaining ...
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8 votes

Diode Clamp failing with LDO Circuit

Alternative design concept: simulate this circuit – Schematic created using CircuitLab You may be able to eliminate R2 if the minimum draw from other circuitry is similar (a few hundred uA). ...
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8 votes

How to calculate aging tolerance of Resistor?

According to the datasheet, the test is done in compliance with MIL-STD-202, method 108 (pp 37-38), condition D (1,000h). This is an accelerated aging test at (probably) 100% rated power (while "ON")...
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8 votes
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Are film capacitors affected by DC bias?

Film capacitors have a very stable capacitance over DC bias. Look at this: But it comes to happen that film capacitors are not the only ones immune to DC bias: So, the actual question is why do ...
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8 votes

Capacitor after Voltage Reference "for stability"

This has to do with loop stability. I won't go into the details of the Barkhausen stability criterion as I think it would go to far for this, but perhaps an analogy can explain what is going on. This ...
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8 votes

What's the impact of a crystal's frequency stability, ESR and load capacitance on micro-controllers?

It would probably be better for you to choose a crystal oscillator rather than a crystal. You just buy it and it works, and is guaranteed to start and conform to stated specifications. If you are ...
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8 votes
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Why is phase margin considered more important than gain margin in dc-dc converters?

For many DC-DC converters there is a "fairly" resonant low pass filter involved at the output and, it changes its phase angle "fairly" rapidly from 0 degrees to 180 degrees over a short part of the ...
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