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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Adding current follower in the circuit: error

I have the below circuit and when I add the current follower op-amp circuit it doesn't work. When I add an ideal op-amp it works, but when changing it to a realistic op-amp it doesn't. What could be ...
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1 vote
3 answers
149 views

Op-amp gain not working as expected

I'm trying to amplify a really small (1.3 mV) voltage from a sense resistor. I am using the following schematic: My load is an LED and resistor. For R2, I'm using a 470 kΩ resistor. For R1, I'm using ...
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How did they consider \$I_{3_{min}}\$ and \$I_{3_{max}}\$ in 4-20 mA current transmitter? [closed]

Define the minimum and maximum currents through R3. See Design Note #5 before defining these currents. For this design, \$I_{3_{min}}\$ = 20 μA, \$I_{3_{max}}\$ = 100 μA are chosen. This link has the ...
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114 views

Simulating voltage divider?

Over the past weeks, I've been looking into an analog method of dividing 2 voltages such that V1/V2=Vout. I found many sources on Google using methods like log and antilog amplifiers or a multiplier, ...
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Why is Hf negative while Vf is positive? Aren't they the same but without Vin?

For the inverting op amp, I've seen the equation Vout/Vin = Hf/Hr Hr is the same as Vr but without Vout. Why isn't Hf the same as Vf but without Vin? What I mean is that Vr = Vout[R1/(R1+R2)] and Hr = ...
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2 answers
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Op-amp non-linear Bode plot

The figure below is an op- amp's Bode plot. In the ideal situation, there are no fp1 and fp2 in there. I would like to know why the real op-amp will have these two poles. Is there any document I can ...
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How does feedback factor works in equation V-/Vout

I am asking this question to understand this. It states that V-/Vout is equal R1/(R1+R2) Here : V- is equal 0V. Because V+ is grounded. So V-/Vout = R1/(R1+R2) => V- = Vout*R1/(R1+R2). But V- is ...
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What is the feedback factor in the inverting Op Amp?

I've got a question about feedback factor. Because I don't know how to calculate it. I've been talking with some people and they say that feedback factor here is equal -R1/R2. Which is the reverse of ...
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3 answers
94 views

Buck converter adjustable output-voltage using digital potentiometer

I am trying to design a buck converter using an LM2576HV (Vref: 1.23 V) and a digital potentiometer (input: 48 V, output: 0 to 48 V, Imax= 3 A). The digital potentiometer with the highest supply ...
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1 answer
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Asking experience for this flow-through pressure sensor: 26PCAFG6G - Honeywell

I have the following sensor:26PCAFG6G The output of the signal is a differential output from a Wheatstone bridge with 0 - 1 psi, or 0 - 70.3 cmH20 corresponding to 0 - 16.7 mV, I am using AD623AN for ...
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1 answer
51 views

Does increasing gain of an op-amp improve transient response speed?

Consider a simple op-amp in a feedback configuration. You can consider the op-amp to be dominant pole compensated and approximated as a first order system. Let's say that the transient performance (...
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Is a buffer stage needed in this signal chain?

I am designing a signal chain that includes a 4 pole cascade Sallen-Key filter based on the AD8034. The circuit will be used to shape tail pulses (~10ns rise time, ~50us decay) into gaussians. The ...
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Operational amplifier controlled LED voltage (power supply)

I am trying to use two APEX PA12A to control two groups of IR LEDs. I have this circuit: PA12A to take the PWM 0-5 V control signal to limit the power supply to LEDs. The thing is even when the PWM ...
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5 votes
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Is this cascoded opamp structure unstable by design (LTspice)?

I am playing with a cascode op-amp design and I have problems judging its stability (schematic at the end of the post). When I judge the DC or AC analyses, it all looks good. No peaking and good phase ...
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Adjusting output voltage feedback with a Howland Current Pump

I'm designing a variable bench power supply using the LT3790 IC. My requirements were adjustable from 1 V to 24 V in 10 mV steps, and a current limit adjustable from .05 to 5 A in steps of 5 mA. I ...
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102 views

Why is this op-amp outputting such low voltage?

Why am I not getting the expected gain out of my op-amp? I m using a 16-pin TI OPA4322SAIPW op-amp with a Advanced Photonix 019-141-411-R photodiode and this circuit: where Rin is 1.8 kΩ and Rf is 27 ...
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2 answers
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Need help to understand op-amp input resistor and capacitor network

I'm trying to understand the circuit design from this application note. Here is the figure: The author said: Resistor RIN provides a dc return path for the VS/2 reference voltage and sets the ...
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Current mirroring in diff amplifier

Hi , I tried to design simple current mirror (load) based differential amplifier. I was trying to make it for optimum swing limit. In the first image as you see I used an ideal current source . I was ...
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1 vote
1 answer
139 views

How to calculate op-amp circuit when there are two feedbacks?

I've got a question: how should I solve this? I've seen a thread were it was solved, but I don't know why the V+ is equal = V+ = Vout+(Vin−Vout)*R/(R+Rs) Like here: How are positive and negative ...
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Why does PMIC temperature increase drastically when opamp gain is increased?

I have an RF signal conditioning circuit that uses two AD8065 opamps for coarse gain. The board is powered via +/-12V, and is stepped down to +/-6V using MC7906 and MC7806 PMIC. The gain is controlled ...
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Analog signal conditioning circuit selection for STM32F2 microcontroller ADC inputs

This is my first time designing an analog signal conditioning circuit for ADC inputs. The card will have up to eight analog inputs connected to eight STM32F207ZG ADC channels (stm32 mcu datasheet). ...
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1 vote
1 answer
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Eddy-current input to op-amp misses reading at times

The problem is only in the input stage of the op-amp. Edited: removed reference to "eddy-current" and changed to "reluctance". The reluctance-current is generated from two coils by ...
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Feedback capacitor vs Miller capacitor in discrete op amp circuits

This is an overly simplified operational amplifier circuit with a feedback applied. The common way to make it stable is to add a dominant pole to the transfer function usually in a form of a Miller ...
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Help understanding TL082 pre-amp/tone circuit

I am trying to construct a small 5W guitar amplifier with tone control as an introduction to audio electronics. I have taken two openly available circuits and I am trying to reverse engineer and ...
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-3 votes
1 answer
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Cascading opamps to drive a MOSFET [closed]

I suppose, this is a continuation of this question: Parallelizing opamps for higher precision For the moment I'm leaning towards cascading opamps by implementing a Composite Amplifier, albeit a lazy ...
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-1 votes
1 answer
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Compare same signal with different voltage thresholds using op amps [closed]

I would like to use two op amps to drive a transistor when receiving two different voltage ranges from the same input signal for a project. For example, I would like to switch the transistor on when ...
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Slow slew-rate compared to the datasheet

I'm trying to create a 10 kHz PWM signal through use of op amps. In the output I'm using a TLV272IP op-amp working as a comparator: Since it has as slew rate of at least 1.8 V/us this should give a ...
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1 answer
52 views

Impedance of buffered LC filters?

I am wondering if its possible to buffer LC filters? I am also wondering about the I/O impedance of the LC filters if you can buffer them. I do know the component values you pick for the LC filters is ...
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2 answers
101 views

0 dB Bode plot as a reference in an academic paper

I want to compare the calculated bode plot of an inverting op-amp with the simulated one, on the 1 mHz-200 kHz spectrum. As expected, theoretically there is no stray capacitance on the circuit above, ...
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1 vote
1 answer
97 views

Op-amp wrong output

I have imported a Spice model of an op-amp from the link below and tried to plot the same outputs, but I am getting different results. Link to the Spice model I used and the desired plot: https://www....
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7 votes
1 answer
315 views

Parallelizing opamps for higher precision

Is there a known way to parallelize opamps for higher precision? Say, for example, I have the typical opamp driving a MOSFET as a follower: Now, for the sake of the argument, on average, the NMOS is ...
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-2 votes
2 answers
94 views

LM324 op-amp input current [closed]

What is the input current of an op-amp (LM324) if I drive it using 5 V?
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1 vote
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How to represent a circuit as a custom part in OrCAD?

I need help in creating a custom part in OrCAD, so far I know how to design a custom part but I don't know how to convert a circuit into a custom part. Example: below is an opamp internal circuit I've ...
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6 votes
4 answers
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Using an op-amp in an unusual configuration with (inverted) negative feedback to the non-inverting input

Here is a question for those who understand unusual, non-conventional op-amp configurations. Is there any reason an op-amp can't be configured with an input going to the inverting input, and the ...
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3 votes
1 answer
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Transfer function of OTA based neural signal amplifier

I was reading about OTA based neural signal amplifiers and reached this schematic Based on the book's description the transfer function for this circuit design is : but unfortunately couldn't find ...
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-1 votes
1 answer
30 views

In PN ADL8107, RF input Pin and Ground showing shorts while checking contunuity test? [closed]

We are using an amplifier of this PN ADL8107 for our application. When we check the continuity testing from input Pin (3) and Grounds (2,4,7,5) by Fluke multi-meter, it is showing short between them ...
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3 votes
2 answers
274 views

Strange waveform observed using push-pull configuration when connecting an inductor

I connected an inductor to the output of a simple class-B transistor amplifier, which was discussed in a Renesis application note. Then I applied a pure sinewave signal to the input and I observed a ...
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1 answer
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Unit buffer op-amp fails with my sensor module signal

I have purchased a pH sensor board and it gives me an output in millivolts. I want to read this using an Arduino. Usually this boards outputs from 400-1200 mV. When I use a multimeter, it gives me a ...
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2 votes
1 answer
85 views

Converting DAC voltage to eurorack voltage

I've connected a DAC to a Raspberry Pi. The DAC gives a voltage between 0V and 3.3V. I would like to convert this to an eurorack voltage between -5V and +5V. Using the op amp calculator at ...
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0 votes
1 answer
60 views

LTspice convergence [closed]

I am working on a power amp circuit that uses an op-amp. My circuit was working fine until I realized I was using a universal op-amp, I am actually supposed to use an LM741. After replacing the ...
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5 votes
2 answers
225 views

Instability of fully differential op-amp in LTspice

I tested the following circuit including a fully differential op-amp for stability in LTspice. The circuit has an inverting gain of 6 and a roll-off at 4 MHz. When exciting the circuit with a step, ...
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2 votes
2 answers
49 views

How do I know what each pin represents in a Spice model of an op-amp in OrCAD?

I have imported a Spice model of an op-amp into OrCAD, but the part symbol is different from what I am used to, and I don't know what pins 4, 5, 8, and 11 represent here. Link to spice model I used: ...
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3 votes
3 answers
463 views

Need help with understanding constant current control circuit

I am an electronics noob struggling to understand a circuit I have reverse-engineered from a circuit board. The circuit will power up a spectral lamp with a current control from 0-25 mA. From what I ...
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0 votes
1 answer
78 views

Lux meter 50 Hz sine noise filter

I've built the circuit with diagram: I used R1 10 MΩ instead of 50 kΩ to get a higher gain. I wanted to measure light intensity, so I'm interested in DC output ...
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6 votes
4 answers
424 views

Op-amps in series – why does this op-amp subtractor not subtract?

Some perhaps overly detailed background: I have a Very Expensive Black Box™ piece of lab equipment that I can control via analog voltages in the range [0, 10] V. It has two inputs that are relevant to ...
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7 votes
3 answers
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What are the purpose of the extra diodes in this peak detector circuit (LM1815)?

This is the circuit diagram from the LM1815 datasheet. I understand everything in this circuit except for the two diodes that I have marked with red. They are in a peak-detector circuit, but all of ...
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3 votes
1 answer
59 views

Altium Singular Matrix warning & Simulation Crashing

I'm trying to make a guitar pedal and I'm working on the input stage op-amp. I keep getting a singular matrix error at resistor R5. Also, the simulation states <...
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0 answers
44 views

Same circuit but different results

To measure a 440VAC voltage, I am using a 2ma/2ma transformer. In the PCB I am using 3 exactly the same circuits to measure voltage in a three phase system. To test the circuit, I measured output of ...
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0 votes
1 answer
32 views

Dupicate LFO Signal and Invert, keeping MAXs and MINs

Im working on a Dual LFO with "Depth" and Rate controls. I already got the "root" LFO signal working and if I do this, I can generate the LFO swinging from 0v to 9v... and with ...
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4 votes
2 answers
111 views

Operational amplifier using power supply current as output [closed]

I have come across a circuit (I am not allowed to share it) with an opamp that uses a special output. The opamp's output is loaded with a resistor and has no other connection. It is the current drawn ...
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