Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers, which are DC-coupled, high-gain electronic voltage amplifiers with a differential input and, usually, a single-ended output.

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74 votes
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Reasons not to use a 741 op-amp?

Simple enough question. Why not use a 741 op-amp in a target circuit or anyone's target circuit? What are the reasons not to use it? What might be the reasons to still choose this part?
Andy aka's user avatar
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0 votes
3 answers
2k views

Op-amp: Virtual ground principle and other doubts [closed]

I can't understand some stuff about op-amps. Here is my list of doubts: If an op-amp amplify the difference between the V+ and the V-, how can it work if for the principle of virtual ground V+ = V-, ...
user11579389's user avatar
2 votes
1 answer
710 views

Transfer function of a LM380 power amp

This is an exam question. Our professor has some generator of tests and out of the blue this beast came. We couldn't ask for the clarification, being an exam question, but from what I can see it ...
rkcepelin's user avatar
22 votes
5 answers
40k views

Difference between differential op amp and comparator

What is the difference between a differential op amp and a comparator? I know a comparator can only give me two values (the supply values). The differential op amp amplifies the difference between ...
user25282's user avatar
  • 277
3 votes
3 answers
10k views

How does this Push-Pull amplifier work?

I'm reading about op-amp circuits that use negative feedback from this article (question no.19). What confuses me is that the negative feedback for the Op-amp (which is being used to reduce ...
Sumanth's user avatar
  • 389
25 votes
4 answers
3k views

Illustrating op amp feedback without control theory

We are teaching op amps in a high school class, before calculus. So we can't use control theory to teach how op amps respond. All the same, I would like to have an intuitive explanation for how a ...
Dov's user avatar
  • 1,661
11 votes
3 answers
54k views

Analog voltage level conversion (level shift)

I have a joystick that puts out analog voltage somewhere between 1.5V and 3.5V. I want to transform this range of voltage to control a motor controller that takes analog voltage between 0V and 5V. ...
jfenwick's user avatar
  • 221
29 votes
6 answers
30k views

Does this photodiode circuit work?

Oli used this circuit in an answer, and it pops up a lot on Google images too. But does it work? If it does a theoretical explanation will be welcome.
stevenvh's user avatar
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40 votes
6 answers
17k views

Designing a *linear* MOSFET driver stage

I'm looking for a MOSFET driver circuit that can be placed between an op-amp and a power MOSFET to operate the transistor as a linear amplifier (as opposed to a switch). Background I'm developing an ...
scanny's user avatar
  • 7,122
6 votes
5 answers
5k views

How to calculate the frequency of oscillation of this low-pass phase shift oscillator?

In the following phase-shift oscillator a low pass network is used instead of a high-pass network. simulate this circuit – Schematic created using CircuitLab Usually the frequency of ...
Physco111's user avatar
  • 629
17 votes
6 answers
49k views

How are positive and negative feedback of opamps so different? How to analyse a circuit where both are present?

In an opamp, feedback on the positive input places it in saturation mode and the output is of the same sign as V+ - V-; feedback on the negative input places it in "regulator mode" and ideally Vout is ...
Mister Mystère's user avatar
16 votes
6 answers
22k 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) ...
svilches's user avatar
  • 529
10 votes
6 answers
9k views

How do I sample a -2 V to +2 V analog signal with a PIC microcontroller?

I am using a PIC micro with a 10bit ADC to take readings from an analog signal with a frequency less than 300 hz. However that analog signal is in the range of -2 V and +2 V. How can I condition the ...
user2200's user avatar
  • 101
4 votes
8 answers
8k views

Why is op-amp output not zero if inputs have the same voltage?

I have started learning about op-amps and have a question. If Vout is the gain times the difference in voltage at the inputs, why is Vout not always zero if we assume the voltages at the inputs are ...
Nicokofi's user avatar
  • 169
3 votes
7 answers
4k views

What is the purpose of the opamp in an integrator circuit?

What is the exact role of opamp in an integrator circuit....?
partykid's user avatar
  • 349
12 votes
1 answer
1k views

What is the difference between "opamp" and "comparator"?

In electronic part seller websites, I see that there are two separate categories for opamps and comparators. As far as I know, an opamp itself is already a comparator if you don't connect a negative ...
hkBattousai's user avatar
  • 14.1k
11 votes
6 answers
18k views

How does this constant current sink actually work?

I have implemented a constant current source and it works wonderfully, but I was just hoping to try and understand it a little bit more! Here is the circuit in question: I have tried doing some ...
MrPhooky's user avatar
  • 2,188
2 votes
2 answers
12k views

Op-amp with T network in the feedback path

How do I calculate the equivalent T network resistance of the inverting amplifier below? The answer is 10 MΩ, but I don't know how to calculate it. I'm not looking for just a formula, but an in-depth ...
user avatar
2 votes
2 answers
1k views

What is the idea behind the ingenious Widlar current limiter?

For a long time, I had the idea of this circuit as a short circuit protection. I first saw it in the output stages of the Widlar's 301 and Fullagar's 741 op-amps... and knew it was Widlar's invention. ...
Circuit fantasist's user avatar
2 votes
2 answers
601 views

Differential vs non-inverting op amp advantage

Assuming I need to measure and amplify a voltage drop over a resistor that is connected to ground on one side (no negative voltages, since current flows always in one direction), is there any real, ...
Łukasz Przeniosło's user avatar
0 votes
4 answers
2k views

Op-amp rail-to-rail voltage follower latching up

I have selected a TS922 op-amp to use in a voltage follower configuration. The specs for the TS922 in summary are: Rail-to-rail input and output Low noise: 9 nV/√Hz Low distortion High output current:...
IanF's user avatar
  • 11
34 votes
5 answers
81k views

Choosing resistor values for 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 resistors ...
dr3patel's user avatar
  • 1,640
30 votes
2 answers
5k views

How to disable a single op-amp in dual packaging?

I am using a dual op-amp package in a circuit, however I only need to use one. Is there anyway to disable the other op-amp so it doesn't inject electrical noise in my circuitboard? I think grounding ...
user1207381's user avatar
25 votes
2 answers
29k views

Single supply op-amp audio amplifier

I am trying to create an op-amp amplifier that would work from single 5V supply, and would be able to amplify -100mV to +100mV audio signal to around a 1V peak-peak or so. I've came across this ...
Golaž's user avatar
  • 2,007
24 votes
3 answers
147k views

What is "offset null" in IC 741?

What is Offset null in 1st and 5th pin in IC 741 (Op-Amp)? Why it is used, though it is not used in many circuits? Give me explanation regarding the offset null! Why offset voltage was formed in IC ...
Abishek ram R's user avatar
24 votes
2 answers
78k views

How do I correct the offset voltage of op-amps which have no explicit offset-null pins?

Not all op-amps have explicit offset-null support, but all op-amps have an offset voltage. This is exactly my practical circuit: How do I correct the offset voltage of TL084 in this circuit? (...
hkBattousai's user avatar
  • 14.1k
10 votes
3 answers
5k views

How do we create current sources?

Constant current sources (simply, current sources) are useful and necessary devices. They are widely used to drive LEDs, charge capacitors and batteries, to bias differential amplifiers, etc. The only ...
Circuit fantasist's user avatar
6 votes
4 answers
46k views

How do you determine the input impedance for an inverting amplifier?

Essentially I am getting confused trying to do the sums for an op amp with a gain of 10dB and an input impedance of 1kohm. I worked out that \$\frac{V_{out}}{V_{in}}=-\frac{R_{2}}{R_{1}}\$ because \$...
Magpie's user avatar
  • 165
4 votes
5 answers
5k views

Understanding Op-amp Negative Feedback

Have a look at the diagram above. It shows an op-amp with negative feedback. Ignoring the feedback loop for now, the voltage (pressure) coming from the 5V battery, acting on the inverting pin, ...
Buck8pe's user avatar
  • 1,694
2 votes
3 answers
919 views

Help understanding how op amps work

I've just been introduced to op-amps and am having a little trouble understanding exactly how they work. Take this circuit, for example. Suppose that there's a 1V source here. Without the op amp ...
Servin Vashnar's user avatar
0 votes
1 answer
502 views

Unable to generate AM wave using opamp log antiog multiplier

I was trying to make a op amp based AM modulator. I used a log anti-log multiplier to generate the below waveform. This is the output I am getting as from this circuit What I intended to generate
Amal Pavithran's user avatar
30 votes
2 answers
20k views

Do op amps need one bypass capacitor or two?

As with other ICs, it's standard practice to place bypass capacitors near the supply voltage pins of op amps. But I've seen conflicting opinions on how to properly bypass an op amp (here, for example)....
Adam Haun's user avatar
  • 22k
30 votes
5 answers
5k views

What's the uA741's appeal?

OK, so the uA741 is 42 years old now. For its time it may have been a great opamp; the requirements weren't as high as today, and there was far less competition. But I was wondering what's the 741's ...
stevenvh's user avatar
  • 146k
18 votes
6 answers
68k views

Why is feedback required in op-amp circuits?

I understand that, in order for an op-amp to function correctly, a DC feedback loop from the output to either the inverting or the non-inverting input (depending on the external circuitry) is required....
user1083734's user avatar
15 votes
3 answers
55k views

Scale 30-50 mV signal to 0-5 V range

I have a CO2 sensor that output signal values 30-50 mV. I need to translate these voltages to 0-5 V for my microcontroller with the highest resolution. I understand that I can amplify the voltage ...
neufuture's user avatar
  • 393
8 votes
3 answers
48k views

How to amplify and offset the voltage in an opamp?

I need to amplify a voltage, which comes from a DAC and is 0-2.5V and scale it 0-25V in an operational amplifier. After amplified, I need to offset it -1.25V, so the final voltage is -1.25 to 23.75V. ...
hjf's user avatar
  • 1,079
5 votes
3 answers
1k views

Current source with unlimited cap drive op-amp oscillating

I've been trying to make a current source, and have finally gotten my hands on some LM8261's which should be an 'unlimited cap drive' op-amp. The problem is, it is still oscillating. This is the ...
Linkyyy's user avatar
  • 1,193
4 votes
2 answers
4k views

How to choose resistor values in op-amps

Ok so my question is what resistor values should I choose for this amplifier. Vin is 0.5Vpp, 50kHz and the desired Vout is 25Vpp, so the overall voltage gain is 50. I know that the voltage gain for an ...
BeatriceUK's user avatar
4 votes
3 answers
5k views

How to electronically generate exponential and logarithmic functions

i mean, it is possible to generate with Op amps, or diodes, etc, to generate complex exponential and logarithmic functions, like one can create sinusoidal signals using a Wien bridge oscillator. ...
Sebastian Valencia's user avatar
3 votes
4 answers
22k views

Voltage Controlled Current Source integrated circuit? Exists?

Does anyone know of a Voltage Controlled Current Source IC? Or do you know how I can build one with as few other components as possible taking up a minimal amount of space? current range needed is ...
Peter Clyde's user avatar
2 votes
3 answers
7k views

How to produce sawtooth waveform from square waveform?

I have a question pertaining the changing of square waveform to sawtooth waveform using OpAmp. Following the picture below, I have to create a sawtooth waveform from a square waveform. It seems that ...
GordonJun's user avatar
2 votes
5 answers
4k views

Design of a discrete BJT current buffer for low-current op amp

I built and simulated this BJT current buffer for an opamp based on examples I found in various places online: Link to simulation of above schematic It simulates fine, but I am pretty sure it will ...
Frosty's user avatar
  • 1,037
2 votes
2 answers
2k views

Op-amp speed: bandwidth vs slew rate

I was learning about the difference between op-amp slew rate and bandwidth. Everywhere it says slew rate is a large signal parameter and bandwidth is a small signal parameter. I have few questions: ...
Confused's user avatar
  • 2,263
1 vote
2 answers
4k views

Making dual power supply from single for opamp?

For the circuit of opamp 741. we have to supply the dual power for it. How can I make a dual power supply from single. For example, make a (+9V)-GND-(-9V) from single 9V battery ?
T.Nhan's user avatar
  • 301
48 votes
2 answers
166k views

What is input and output impedance of an opamp?

I have never understood input and output impedances of an op-amp. If anyone can explain what these two terms mean in an op-amp I'd highly appreciate it. Thank you! http://www.eecs.tufts.edu/~dsculley/...
user734861's user avatar
30 votes
6 answers
15k views

What is noise gain, really? And how is it determined in the general case?

UPDATE: This question triggered what might fairly be called a research obsession for me. I've gotten pretty close to the bottom of it I think, I've posted my findings as an answer below. There was a ...
scanny's user avatar
  • 7,122
24 votes
1 answer
55k views

What's input bias current in opamps?

Is it the current you have to drive in the input to get a specific, defined voltage at the output? And don't the currents cancel each other when applied to both inputs?
Federico Russo's user avatar
21 votes
5 answers
43k views

Inverting buffer with op-amps

I know that it's easy to make a unity gain buffer with an op-amp (as a voltage follower): simulate this circuit – Schematic created using CircuitLab I also know that it's easy to make an ...
Greg d'Eon's user avatar
  • 3,827
18 votes
1 answer
37k views

Subtracting two voltages using an op-amp

I'm essentially a digital guy, and am used to using a comparator to compare two voltages and give a high or low depending on their relative values. Now instead I want to subtract one voltage from ...
tcrosley's user avatar
  • 48.1k
18 votes
8 answers
16k views

Op-amp input resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is an instrumentation amplifier that apparently uses an inverting amplifier's output instead of a ground ...
In silico's user avatar
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