# 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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0answers
16 views

### What is the center frequency and Q-factor formula for gyrator equalizer?

I made an equalizer circuit as per the given schematic and now I want to change the center frequencies of each stage by changing capacitor values. I cannot find the formulae for frequency and Q online....
1answer
363 views

### Why does an opamp buffer output voltage with no input?

I have an opamp (specifically a TL072) I'd like to use as a high impedance buffer for a digital filter circuit I'm building. When I power the opamp with +5/0 on the rails configured as a unity gain ...
0answers
51 views

### help on op amp circuit analyze

Please help me analyzing this circuit. It should be used in very low AC voltage as input, and output some precision dc output to be measured with adc. Diodes should be 1n4148 as I suppose. I need ...
1answer
51 views

### Mysterious current appearing on Ltspice using LT6018 opamp

Do you have an idea of where the 120 mA current (going through Cact) is coming from ? I just can't understand how the LT6018 can output that much when the datasheet says it can output max 50mA. Even ...
0answers
129 views

### How to amplify sine wave with op-amp

I am trying to build my own function generator. I put together a Wien bridge oscillator but I get very low output voltage. I wanted to connect it to an op-amp to simply increase it. I connected the ...
2answers
32 views

### Am I measuring the Op-amp MCP6004 IC output voltage correctly using Arduino

Right now I am testing an MCP6004 Op-amp IC. A sensor in my main circuit going to give me a signal in the range 0-0.5 V max. So, I want to amplify this in the 0-5V range so that my Arduino reads it ...
0answers
37 views

### Is the output resistance of the first amplifier the input resistance of the second amplifier?

If I cascade a MOSFET based amplifier with another one to form a multistage amplifier, then in small signal analysis, will the output resistance of first amplifier become the output resistance of ...
2answers
43 views

### Transient DC current on mixer output

I have an audio mixer with the following circuit (I omitted the input stage): I removed the mono instrument output and used the jack connector as an alternative line-output. However, while doing so, ...
2answers
106 views

### Series resistor on op-amp input

There is a related question similar to mine: Op Amp input protection, but I found this other configuration: where the series resistor is placed after the TVS diodes. What is its purpose? The input ...
1answer
51 views

### Protecting unpowered op-amp, or how can I use 12V to switch 3.3V?

I'm designing a Eurorack synthesizer module which includes an MCU, DAC (TI DAC8565), and TL074 op-amp for scaling and buffering the DAC output. In normal operation the module will operate from a +/-...
0answers
36 views

### Bootstrapping low voltage opamp

I was analyzing the below circuit. In this circuit an opamp supply voltage (V+ − V) = 16V is powered by using a 45V supply and a -5V supply. I understand the circuit to some extent. Here U1 is supply ...
0answers
19 views

### Usage of LM 723 as High Voltage High Current voltage (HVHC) regulator, High Voltage Low Current(HVLC) and Low Voltage High Current voltage regulator [duplicate]

I have been asked to make a presentation on LM 723 as High Voltage High current regulator and high voltage low current regulator(I know the ic is way too old but its in our university syllabus so I ...
2answers
68 views

### How to solve this non ideal inverter opamp?

it is asked to make a non ideal inverter opamp that has an input of 2mV or and get an output of -100mV, so I think the next circuit should suffice. simulate this circuit – Schematic created ...
0answers
39 views

### opamp single supply output AC (audio) voltage limit

I build non-inverting op amp with single supply voltage cca 9V. The basic scheme is shown in the figure below: How to limit output AC signal if the base DC voltage is at half the supply voltage 4.5 V ...
2answers
57 views

### How to size overcurrent protection?

I'm a begginer in electronics so I have some very basic questions. I would like to protect an OpAmp power supply rails from overcurrent. But I don't know at what value I should set this protection. ...
2answers
101 views

### How do I create ground voltage for my op-amp?

I am trying to create a practical Wien Bridge Oscillator and I created a simulation for it. Everything works fine in the simulation. Then I proceed the real part. Since I have only one power supply, I ...
0answers
56 views

### Does riding the rail fatigue an opamp?

I have an LM7332 that is creating a gate voltage to drive a MOSFET. The circuit failed in the field and I'm trying to debug. One thing I've noticed is that the supply voltage to the MOSFET was ...
1answer
78 views

### Isn't conventional current supposed to go from high potential to low potential ? If yes, then why this rule is not respected in opamp using AC?

First, thank you for reading my post. I'm a beginner in electronics. I learned that conventional current goes from high potential to low potential. It has always worked for me in DC and even AC. But ...
1answer
31 views

### UC3843 Clamping Error Amplifier Voltage

I'm trying to design a constant current solenoid driver using UC3843 PWM IC. The datasheet is available at https://www.ti.com/product/UC3843 Since I'm only utilizing constant current function using ...
2answers
76 views

### Something is wrong with my Wien Bridge

I want to create a wien bridge oscillator to use in my later projects so I tried to simulate a schematic I found online. Its stated that R1 = R2 and C1 = C2 should be true in order to circuit to ...
2answers
73 views

### Input impedance of the op-amp inverting amplifier [closed]

I have a lab exercise with inverting opamp (gain = 10, R1 = 1k, R2 = 10k). The subject of the lab is to measure input impedance of such amplifier by adding 1k resistor in series to the input and drive ...
1answer
53 views

### Respiratory rate monitor

I have this project to build an instrumentation system to measure the respiratory rate. We decided to use a thermistor to measure the variation on the temperature of the air inhaled and exhaled. To ...
1answer
78 views

### Weird output voltage on op amp triangle wave generator

I am trying to simulate a simple triangle wave generator using the 741 op amp in the following configuration: I'm using ngspice to run the simulation and my .cir ...
1answer
34 views

### How to switch an output based on specified voltage difference (outside of rail tolerance)?

I'm designing a CAN circuit that will connect a series string of 12V batteries together. The first battery will be tied to a common ground (think vehicle chassis) that will connect to the CAN ground ...
6answers
471 views

### In a negative feedback loop, why does increase in v_out lead to increase in v-?

I hope this is the right place to ask this question. (Please let me know if there's a better place to ask this.) Basically, I'm quite confused about how we check if we have a negative feedback loop. ...
3answers
307 views

### Should I buffer my analog input?

I've been using an Arduino's analog input to read a resistance. The resistance is typically from an LDR or from an adjustable resistor. It's working fine so far. I have 10 bits resolution, usually I ...
2answers
70 views

### How do I transform a unipolar signal to bipolar signal?

I am trying to design a circuit that will convert a unipolar 0 - 12V square wave signal of about 1kHz to a bipolar +/- 12V signal. I have tried using a differential amplifier design approach similar ...
2answers
319 views

### Astable multivibrator using op amps - why does it start?

I'm new to electronics and I'm learning some circuits with op amps. Now I have been shown this astable multivibrator. I understand how it works. The op amp is saturated at one side or the other ...
1answer
48 views

### Understanding Negative feedback loop circuit with an Ideal Op-Amp

The following is given as an example of a negative feedback loop in my textbook, note that the op amp is assumed to be ideal. However I do not seem to get the logic behind this acting as a negative ...
2answers
37 views

### Understanding Negative feedback loop circuit with an Ideal Op-Amp

The following is given as an example of a negative feedback loop in my textbook, note that the op-amp is assumed to be ideal. However I do not seem to understand the logic behind this acting as a ...
0answers
53 views

### Ultrasound piezo crystal and doppler for blood flow velocity

I am currently working on a microcontroller based project to measure the blood flow velocity using ultrasound doppler. I have purchased two Spengler 8 MHz continuous mode probes in order to measure ...
0answers
56 views

### Boosting an analog voltage signal

I have a 0-3.3V analog DC signal and want to change that into a 0-5V analog DC signal? How should I go about doing this? An op-amp? DC boost converter? If it is an op-amp, what does the circuit ...
2answers
54 views

### Find Vo of an op-amp circuit

simulate this circuit – Schematic created using CircuitLab I've tried solving for Vo in two ways, one is I took V+ by voltage divider getting V+ = V1(R2/R1+R2) = 0.05V. Since V+ = V-, it follows ...
1answer
118 views

### Why does this opamp have a diode on v+

I was working on a layout for a guitar effect, and noticed on the schematic that 1 opamp has a 1N4148 diode on V+. IC6 on the schematic below. Given it has an internal power supply, I'm assuming ...
3answers
141 views

### Common mode impedance in operational amplifier

While looking at this simulation, as they say no current flows at the non inverting terminal of the op-amp, but looking at the differential stage of the operational amplifier shouldn't there be some ...
1answer
36 views

### Op-amp Power Dissipation Calculation for a pulse output

I am trying to calculate the power dissipation of the op-amp for a circuit as below. I am wondering if I did it correctly. Can anyone provide any tutorial on this? So this opamp will output ...
6answers
690 views

### RC oscillator with op amps

I am a physics student at a university and because of the pandemic, I and my classmates have to simulate our electronics lab exercises in Micro-Cap (version 12). We've got schematics like in this ...
4answers
219 views

### How do i solve a circuit when a capacitor is between in op amp inputs?

I am quite confused with this circuit. Most circuits I have seen don't have a capacitor between the op amp inputs. I tried to write out the differential equations using nodes, but I can't find enough ...
2answers
67 views

### Opamp Compensation For Input Capacitance

I am going through the datasheet of LM7171 for one of my applications. Please see the below circuit. May I know how they arrived at the equation for CF? Is this equation is valid for non-inverting ...
2answers
62 views

### What are the advantages and disadvantages of a Darlington pair? [closed]

Can the BJT transistors in a Darlington pair be of different types?What are the advantages and disadvantages of a Darlington pair? Is such a circuit able to generate power by itself?
2answers
35 views

### Does op-amp open loop gain change with DC input voltages versus small-signal AC input

I was wondering whether or not DC voltages can be amplified by op-amps. I thought about a typical Miller op-amp structure (differential pair input) and I suppose it could amplify a DC voltage. I am ...
2answers
72 views

### What is an op-amp's differential input impedance?

I've heard of differential voltages, but the concept of a differential impedance is new to me. Suppose we are trying to calculate/derive the differential input impedance of the following difference ...
2answers
136 views

### Which is the input resistance of the second amplifier?

If a apply a positive Vs, then D2 is blocked and D1 is working, right? How do I calculate Vo then? I know the formula is: - (input resistance / negative feedback resistor) * Vs, but I don't know which ...
1answer
88 views

### PWM with op-amp, but can't figure out formulas/how it works

I want to make a way to control the high time with a control voltage, instead of using a variable resistor. For this I have found this diagram with an op-amp, and I have tested it in Multisim (a ...
0answers
51 views

### Clarification on amplifiers [closed]

Can I use 2 LM311 in place of 1 LM385mm? LM385MM is a dual operational amplifier and LM311 is a differential amplifier so according to me we can use, it is just that LM385mm is low power device so it ...
1answer
47 views

### Laser diode driver circuit analysis help

I'm looking up for some circuitry to drive my laser diode and I came across this tutorial. I understand the basic operation of this schematic; however, there's one thing that confuses me: I cannot ...
2answers
85 views

### Ideal Op-Amp obeys virtual ground principle without negative feedback?

I was reading this book - 'Fundamentals of Electric Circuits - Alexander, Sadiku'. I came across this: They say that a characteristic of an ideal op-amp is that v1 = v2. I was taught that this is ...
1answer
94 views

### How do you regulate a car battery down to exactly / not more than 12V?

My problem: I want to light up the inside of transporters with a 12V LED strip. But I don't think powering it with the 12V car battery directly is a good idea. Although the name implies 12V, a car ...
3answers
75 views

### Where to connect unused pins operational amplifier

I am using a couple of OPA2227UA op-amps for a analog circuit. Since these are dual-op amps, one of them ended up unconnected. (The +-In/Out B pins shown below): The datasheet says what can I do for ...
3answers
69 views

### Op-Amp buffer Enable/Disable

I am designing an electric veichle controller for a University project. The motor driver receives an analog signal (0-12V) to adjust the speed. I use a digipot followed by a buffer to convert the ...