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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Buffered audio splitter too hot for volume chip

I'm building MIDI controlled effects pedal that autofades the blend amount of a send-return effect loop. Still pretty much a noob on the analog side, so bear with me. Firstly I need to split the ...
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2 votes
3 answers
197 views

Second order active high pass filter

I am trying to design an active filter, which I assume is an active high pass filter according to what I see from the Bode plot. I can get the transfer function from this plot and then I need to ...
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2 votes
1 answer
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Second order low pass filter: two 1st order filters not-immediately cascaded

A second order low pass filter (LPF) can be made by cascading two active LPF (an RC network + opamp.) What happens if, instead of immediately cascaded, an active LPF acts at the input (buffer) of a ...
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Interview Question

This Circuit was given. I know every component of this circuit individually, I know feedback and gain margin and transconductance amplifier. But the problem is how to start? first, I was thinking to ...
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Integrator circuit - no DC path from output to input

Someone told me that this circuit does not work unless there is DC bias path in the feedback. Because the op-amp is operating open loop for DC. Someone also told me that the input transistor pair of ...
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Overall CMRR of analog front-end

My analog front end input consists of a chain of (instrumentation amplifier + differential amplifier + and ADC). Is the CMRR of the overall chain only considered based on the first element that is ...
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What is the purpose of the parallel resistor at the end of this amplifier circuit?

I have this following circuit that I tried to decompose and find the purpose of each component. The op amp is LM6181 and the purpose of the circuit is to reduce the voltage of a probe so it fits ...
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1 vote
2 answers
95 views

Supply voltage for opamp in a current sink circuit

I want to use an opamp in a current sink configuration in order to control the emitter-base current of a PNP transistor via a digital-analog pin from a microcontroller. The circuit is as shown below. ...
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2 votes
2 answers
110 views

Why is the op-amp able to eliminate negative voltage?

I have a circuit with the attached waveform. Can someone please explain why the 2nd op-amp (middle) is able to eliminate the negative voltage? By reasoning and analysing the circuit I can see that the ...
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Single wire electrodynamic pickup preamplifier (transformerless ribbon mic)

I'm currently working on an experimental string musical instrument. It isn't my invention though. The source of inspiration called Dvina has an unusual pickup system. It senses the current induced in ...
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1 answer
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Distortion Pedal Design

I am building a guitar pedal and came across a reference design here: https://www.wamplerpedals.com/blog/uncategorized/2020/05/how-to-design-a-basic-overdrive-pedal-circuit/ I'm not sure why the ...
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1 answer
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Over Current/Short Circuit Protection Using op-amp and MOSFET

I wanted a circuit to limit the current to say 4A, and found this but it doesn't work in the Proteus simulator. What's wrong with this circuit? anyways to improve it? here is my expectation of the ...
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Troubleshooting power amp board

Here's a Sunday electronics puzzle... I'm having trouble finding the culprit on my Gallien-Krueger 2000RB power amp board. If anyone has a suggestion on what might be affecting the highlighted ...
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Constant Voltage / Constant Current / Current Foldback Regulator Evaluation

I am a semi-retired EE in electrical distribution, so op-amps are not in my tool bag, and I could use some help. It has been over 30years since I last worked with them, and I need help from someone ...
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Reduce or filter DC spike and noise

Goodmorning, I have a small voltage drop (about 20-25 mV, DC) on a sense resistor (0.180 Ohm) and I need to amplify this with an op-amp to reach 2-3 V (DC). The signal is not clean and the noise, with ...
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Noise in measurement

I'm having a problem when I measure a voltage from a lead battery. I provide my circuit so you can understand better whats happening. For example I measure a 24 V battery, goes to a resistor divider ...
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Function generator with an operational amplifier

I am solving a function generator whose frequency of each output is 5kHz. My question is, how can I find the parameters of C3, R5 and R6 to get an output of the same frequency? In addition to the ...
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Linear Analog Optocoupler Arrangements

For optocouplers with a second photodiode for feedback for linearization, what is the functional difference between the two positive input stage configurations below? simulate this circuit – ...
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Why does this circuit produce a triangle wave?

EDIT: Op amp is a UA741CP I built a simple square wave generator on a breadboard as shown in the picture below. C = 1 μF R1 = 1k R2 = 10k R3 = 10k Supply voltages are +/- 12V The circuit produces a ...
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1 answer
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On the stability of differentiator based on OP amp with an example from TI manual

I am building a proportional-Differentiator circuit based non-inverting OP-amp. But I am confused with the stability condition of OP-amp. The system will be unstable if the loop gain |T(s)|=|a(s)B(s)|...
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How can negative feedback reduce distortion if A*beta>>1?

I have read that negative feedback reduces distortion (frequency, amplitude, phase) because if \$A \times beta >>1\$ the transfer gain will be \$(A/(1+A*beta)) = A/A \times beta=1/beta\$. Which ...
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1 vote
1 answer
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What's the relevance of differential (and common-mode) input impedance?

Short version: as stated in the subject: what's the relevance of these parameters when designing a "normal" op-amp circuit, for example for audio: a Sallen-Keys active filter, or an RIAA-...
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1 vote
2 answers
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LTspice-RIAA-simulation not working out

I'm trying to simulate a RIAA-phonograph-preamp since I want to build a phono-preamp. I've built everything according to the data provided by LT for the LT1115. But my simulation seems to not be ...
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2 answers
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How do I find Vo in the circuit?

I1 + I2 = I3 I1 = Vi/Z1 ... Z1 = (1+sCR1)/sC I1= Vi(sC)/(1+sCR1) I2= Vi/R1 I3= -Vo/R1 I1 + I2 = I3 Vi[(sc)/(1+sCR1) + (1/R1)] =-Vo/R1 -Vi[(R1sC)/(1+sCR1) + 1] = Vo How do I change back to time domain?
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Replacing a virtual ground circuit with center tapped transformer

I just bought a cheap headphone amp (those 47 Amp). I aiming to replace the voltage-divider-virtual-ground circuit with a 12v-0v-12v transformer (ofc with rectification). I checked the NE5532's VCC+'s ...
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IR remote code amplifier

I am interested in amplifying output mod signal of my tv remote in order to use a higher power led/vcsel. Now, it should be as simple as cutting the emitter led and putting a transistor that would ...
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1 answer
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Where are the transistor number 18 and 21 in op amp 741 according to Wikipedia?

I was trying to implement this op amp from Wikipedia in Proteus : Like this: But I could not find Q number 18 and 21. What is the reason that there are not Q number 18 and 21? Or if this image is ...
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3 votes
1 answer
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Voltage variation in the output of Differential Amplifier

I am working in low side current sensing differential amplifier circuit. VA is connected to ground and resistance R2 is also connected to ground but both the grounds are not same then there is voltage ...
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2 votes
1 answer
105 views

What do I add across the opamp to get a full sine wave?

I'm struggling to figure out a solution to avoid saturation, I believe the solution will require some component to be attached across the opamp to produce the same voltage out as voltage in (voltage ...
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2 votes
2 answers
230 views

Measuring ambient light intensity using BPW34 photodiode and TLC271ACP opamp

I've composed a schematic for measuring ambient light intensity using a BPW34 photo diode (Osram brand) and a TLC271ACP opamp. The output will be read using an ADC entrance of an MCU, so VDD = 5V here....
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Where To Connect Wires on Pin Out

I am very inexperienced in wiring. Where do I connect the wires from my trans-impedance amplifier to my DAQ to measure the voltage out and also to apply a voltage. I don't understand why there are ...
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1 answer
72 views

Op-Amp nodal analysis

Why is i20 = (Va-Vb)/20k, not Va/20k?
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Why there is a resistor connected between terminal and the ground? [duplicate]

Why a resistor is connected between non inverting terminal and ground?
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1 answer
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Need help to understand this circuit

I'm trying to understand this circuit, it's been a long time since I messed with electronics. I even managed to understand some things, for example: The first ICL7660 circuit will be used as a source ...
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1 vote
4 answers
415 views

Can I replace an LM741 op amp with an AD620 op amp in my circuit? [closed]

I have a voltage comparator circuit (shown below.) Can I replace the opamp with an AD620 op amp? My lab has mostly AD620 op amps.
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Current Shunt Amplifier Problem (MAX49921)

I'm currently trying out the evaluation kit for the MAX49921 from Maxim, and I'm having a few problems with it. First thing to note is that my board appears to be an issue a board, but all the ...
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1 vote
2 answers
400 views

Can the connection of collector and base in these circuits be considered as a diode connected transistor?

I was learning how to design an op amp and I saw something thatis called "diode connected transistor." Like this image: Later I saw a person that was teaching about these circuits, and he ...
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Resistor in parallel across a capacitor

I was working through a problem involving two cascaded integrating op amps with feedback resistors with a DC step function as input. The book asks for the current flowing from the capacitor in the ...
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1 vote
3 answers
137 views

Op-Amp with current source input

In this op-amp circuit, the output is defined as \$v_o = - i_sR\$. Question 1 I am slightly confused about how the current flows in this circuit. By the principle of virtual ground, the inverting ...
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2 votes
0 answers
55 views

Current through op-amp feedback resistor

Image source: Fundamentals of Electric Circuits by Alexander and Sadiku. 5th Edition. Page 182 Can someone explain to me how 26.25uA is the correct answer here? I am getting 11.25uA. If I assume ...
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1 vote
1 answer
56 views

Using a square wave function to select output

Im new here! I been having some trouble thinking about a circuit wich selects one of two outputs based in the value of a square wave function like this To put some numbers Freqs Vin=1Hz Vout1=1kHz ...
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2 votes
1 answer
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Why is high open loop gain needed for an Op-Amps virtual ground?

In books, I often see that they state that the op-amp has a virtual ground property when it has a high open-loop gain and in a negative feedback configuration. First Question: The negative feedback ...
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1 vote
1 answer
60 views

Which part of this transistor model op amp represents pin 5?

In this op amp oscillator pin 5 is connected to an RC circuit: I have a transistor model of that op amp and I want to connect an RC circuit to it like the above circuit: Since pin 4 and 8 represents ...
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Why in this circuit the collector of Q2 is receiving negative voltage?

According to when we say the collector in a transistor is reverse bias and the base and emitter are forward bias, why in this circuit (since Q3 or Q4 are NPN, so the emitter should be connected to ...
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3 votes
2 answers
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Would appreciate some tips on designing simple OpAmp circuit

I've recently posted this question regarding input impedance when working with DC signal on HCPL-7840 Isolation Amplifier. The answers were very clarifying and helpful, but I've come to realize I need ...
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3 votes
2 answers
125 views

Is a current limiting resistor needed for dual opamp supply pins?

Consider the TL072 dual op amp that is supplied with +/- 12V. The datasheet says that the supply current for (each) amplifier is typically 1.4 mA, with maximum of 2.5 mA. If both amplifiers are ...
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6 votes
3 answers
892 views

Current source with MOSFET

In the circuits below, what does the 100R resistor do? In my understanding the 1K along with the 200 pF create an integrator topology to provide some stability but how about the 100R that feeds the ...
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5 votes
3 answers
441 views

Why is the output voltage in my second op amp not the same as for the first op amp?

I saw this tutorial on a website. From that, I designed these circuits: In my circuits the voltage source is 12 volts. The tutorial says the output gain should be 2. In my second circuit the gain is ...
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2 votes
3 answers
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Does the input offset voltage of an opamp remain same after each power up?

If we have an opamp and we know the input output relation we can obtain a linear function even though there is input offset voltage. In the above situation as long as we know Vio, and since resistors ...
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3 answers
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In this image where is the base of Q3 connected to?

In this image the base of Q3 shows an arrow that points to the 10k resistor, but I do not know where is it connected to. Image: According to that image I do not know what should I do with the base of ...
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