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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66 votes
8 answers
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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?
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3 answers
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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-, ...
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2 votes
1 answer
550 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 ...
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22 votes
5 answers
35k 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 ...
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25 votes
4 answers
2k 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 ...
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11 votes
3 answers
51k 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. ...
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  • 221
29 votes
6 answers
28k 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.
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38 votes
6 answers
15k 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 ...
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  • 6,852
3 votes
3 answers
8k 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 ...
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  • 379
15 votes
6 answers
47k 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 ...
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15 votes
6 answers
20k 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) ...
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  • 519
6 votes
4 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 ...
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10 votes
6 answers
8k 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 ...
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  • 101
11 votes
6 answers
16k 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 ...
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  • 2,128
0 votes
4 answers
788 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 ...
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21 votes
2 answers
25k 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 ...
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5 votes
4 answers
45k 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 \$...
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23 votes
3 answers
137k 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 ...
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3 votes
4 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, ...
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  • 1,642
2 votes
2 answers
990 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. ...
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2 votes
3 answers
799 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 ...
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33 votes
5 answers
73k 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 ...
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18 votes
6 answers
66k 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....
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23 votes
2 answers
71k 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? (...
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14 votes
3 answers
52k 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 ...
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  • 383
30 votes
5 answers
4k 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 ...
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7 votes
3 answers
2k 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 ...
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2 votes
5 answers
3k 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 ...
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  • 1,029
6 votes
3 answers
38k 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. ...
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  • 1,047
5 votes
3 answers
979 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 ...
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  • 955
3 votes
4 answers
21k 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 ...
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1 vote
2 answers
3k 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 ?
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1 vote
2 answers
224 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, ...
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0 votes
6 answers
4k views

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

So I have started learning about op amps and have a question. If Vout is the gain times the difference in voltage at the inputs how is Vout not always zero if we assume the voltages at the inputs are ...
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44 votes
2 answers
155k 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/...
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26 votes
2 answers
17k 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)....
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8 votes
6 answers
17k views

Is a square wave still considered DC?

Say I have a logic-level square wave, where 0V is "low" and 5V is "high". I'm pulsing this at a constant 60Hz, 50% duty cycle. My intuition says that since the voltage never goes negative, it's a DC ...
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  • 335
20 votes
5 answers
35k 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 ...
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  • 3,767
24 votes
1 answer
54k 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?
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14 votes
3 answers
6k views

What does this op-amp circuit do? (part of an ECG)

I would like create an ECG circuit based on this schematic (from the AD620AN datasheet): I don't know this part of the circuit and how it works. I know this is called a right leg driven circuit which ...
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  • 143
16 votes
1 answer
34k 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 ...
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18 votes
5 answers
14k views

Op-Amp Input Resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is of course an instrumentation amplifier that apparently uses an inverting amplifier's output instead of ...
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11 votes
1 answer
848 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 ...
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28 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 ...
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12 votes
6 answers
19k views

Input voltage range of opamps

I understand that, for an ideal opamp, Vo is bounded by Vee and Vcc (i.e.; Vee < Vo < Vcc). But, what about the input voltage range? What is the allowed input voltage range in which opamp works ...
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9 votes
6 answers
4k views

How does an op amp integrator work?

I know there are at least two questions related to this on stackoverflow but neither really answer my question, and in any case, both questions got downvoted. What I am after is an operational ...
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  • 300
4 votes
1 answer
10k views

Understanding absolute value circuit operation

I'm trying to figure out how this circuit works: It is a absolute value circuit; that is, the output follows the absolute value of the input. In the process of figuring out how it works, I am ...
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  • 1,059
3 votes
7 answers
3k views

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

What is the exact role of opamp in an integrator circuit....?
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  • 349
8 votes
3 answers
933 views

How does the compensation resistor in an inverting amplifier compensate for the input bias current?

I can't see how a resistor placed on a whole other input terminal has anything to do with compensating this input bias. i.e. the input stages are just the gates of transistors of differential stage. ...
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6 votes
2 answers
3k views

Why does bringing TL072/TL074 non-inverting input low cause output to go high?

I was building a circuit using a Texas Instruments TL074 as a comparator, when I noticed some strange behavior. I isolated the chip and tested it with a couple of potentiometers. Basically, when I put ...
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