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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Calculating resistor and capacitor values for an op amp differentiator circuit design

I need help in designing a differentiator using an op-amp. I know that the equation for an op-amp differentiator circuit is Vo = RCdVin/dt, but I don't know how to calculate the component values to ...
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Why is the LM741 operational amplifier so prolific? [duplicate]

Possible Duplicate: What's the uA741's appeal? The LM741 seems to be the "prototypical" OP-AMP used in teaching basic analog electronics. Why is this chosen when better designs are ...
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Systematic construction of the ODE system of a circuit containing opamps

I want to compute the voltages and currents in a circuit containing R,L,C, opamps and voltage sources. I perfectly understand how to do this for circuits containing only R,L,C and voltage sources, ...
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7k views

Getting PWM with an astable multivibrator (square wave generator)

I would like to use this schematic: to create a square-wave generator but I would like to modify it by getting an output that runs from 0 to +5V, as well as changing the signal so that I can change ...
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10k views

What does the term "slow drift" mean?

Good night everyone. I came across the term "slow drift" when reading a paper on an electronic design, and I am not quite sure what it means. The author said he used a low pass amplifier to remove ...
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A good 3V single supply OpAmp recommendation for a transimpedance amplifier

I have designed a transimpedance amplifier using OPA355, the datasheet suggest this Opamp can go down to 2.5V and still works however I cannot get it to work at 3V. If I provide 5V supply, everything ...
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Amplifying and filtering a very low frequency signal(Bandwidth of 4Hz)

Good night, everyone. I want to amplify and filter a signal that has a bandwidth of 3.5Hz and is of the order of 5 - 40 milliVolts. I plan to amplify the signal before filtering it so as to prevent ...
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Basic 741 Op Amp Question

I am trying to build a basic 2 input summing amplifier using radio shacks 741 op amp. I have a feeling I damaged my IC chip through my wacky experimentation's. But lets run through the math just in ...
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PH differential instrumentation amplifier

I have a computer engineering background with minimal experience with real EE work. I want to interface to a ph probe and was wondering what the best way to do this is. It seems to me there are 2 ...
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Unity Gain Op Amp outputting odd voltage

I have an op amp set up in a unity gain, or buffer, configuration like so: Unity Gain configuration Op Amp http://img580.imageshack.us/img580/2389/opamp.png The op amp is tied to 3.3V and GND, I am ...
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What is the purpose of this op amp?

I am trying to build a pH meter using the below circuit. I am trying to understand the function of Op Amp U1. As I understand it, the LM4140A-1.0 is a voltage reference outputting 1.024V, which is ...
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Can I provide a negative input voltage to this (or any) ADC?

I have a pH probe which is a high impedance voltage source of which I want to measure in increments of 0.5mV (500uV) with an ADC. This voltage can swing between +/- 1V. I have chosen this ADC as ...
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I understand that having an capacitive load at the output of an op-amp can potentially make the circuit unstable. However, how can I go about calculating this? For instance, I'm trying to design a ...
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How do I condition a signal with an op-amp that needs a negative rail where one is not provided?

I am working on a water monitoring system that needs to read ph in ADC of microcontroller(0-3.3V) I understand how ph sensors work...just -.41V(0ph) to +.41V(14ph)... I have an understanding of ...
• 207
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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 ...
• 189
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Adjustable linear led driver? Linear, not PWM

I'm working on a product that requires an led to output currents varrying from 0mA to 350mA and as many possible levels in between (~1000 would be sufficient I suppose). I CANT output a PWM signal to ...
• 189
20k 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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Is it considered a hack to use an op-amp in place of a relay?

I have an application that would traditionally be solved by the means of a relay. I have a 12 VDC load that I would like to switch on and off via a 5V microcontroller pin. But, I'm already using some ...
• 163
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Twin-T Active Notch Filter Analysis

Could anyone give me a hint in analyzing the Twin-T Active Notch Filter? I tried a delta-star transform, followed by nodal analysis, but ended up with conflicting equations. For an example, look at ...
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Strain Gauge with Instrumentation Amplifier question

I have a problem making a circuit like this working I got it from this TI application note. For testing purposes I have set: $R4=R2=R3=R1=47 \Omega$ $Rf = 10 k\Omega$ $Rg= 26.70\Omega$ ...
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Phototransistor OpAmp - compensating for ambient light

How to automatically compensate (LDR?) for ambient light so as to eliminate the need for adjusting manually with potentiometer.
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Error in this explanation of instrumentation amplifier?

On this webpage I read an explanation of an instrumentation amplifier: The negative feedback of the top op-amp causes the voltage at Va to be equal to the input voltage V1. Likewise, the ...
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35k 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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Driving hard drive voice coil actuator with PWM

I have been trying to control a voice coil actuator with PWM input, but i have the following problems and would like you to correct or point me in new directions. I have an arduino which outputs PWM ...
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How it is possible to make bad audio amp?

After discovering how great op amps are, and that some extremely good ones--especially at low power levels--are available at reasonable prices, I wonder why all audio amplifiers, big or small, don't ...
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Negative voltage from Arduino?

I recently got a INA101HP see picture below. I was trying to use it on a breadboard. To power the op amp I connected 5V to +vcc pin but then I realized I did not really get how to provide -5V for the -...
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Simple VU meter with Lm3915

I'm making a VU meter with an LM3915 and I would like to be able to plug my computers audio output into the LM3915 directly and get it to register. I've been searching the internet for a design but ...
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How to make LED bar graphs to measure intensity

I'm working with this design. I would like to make those LEDs into LED bar graphs that will show the intensity. For example, I want a song with a loud base to make the bar graph shoot up to the top. ...
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1 vote
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Can I replace MC33204P with one of these other op amps?

I'm working to make this schematic and I was wondering if it is possible to swap out the MC33204p with either LM348N or LM339AN. And if you could let me know why swapping them would still work I'd be ...
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How can I best amplify a signal from my headphone jack to operate a relay 3-32VDC?

I'm working with the following op-amps: LM308AN LM358P UA741CP I want to make a small box that will control the power to any string of christmas lights based off of music that is playing. I would ...
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How to increase max input current of logarithmic amplifier 10x-100x safely?

Is it possible to increase max allowed current of logarithmic amplifier to say 1A by some workaround without loosing capabilities in lower range: 0..1ma ? For example the TI part LOG112 has few ...
14k views

Phototransistor transimpedance amplifier

I have a typical NPN phototransistor. I have it working in a common-collector configuration; see figure 2 of this app note. Increasing Re will increase the sensitivity, but decrease the speed. I ...
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39k views

How to make a clean amplified microphone analog to digital conversion?

I've asked a couple of questions relating to this project the past couple of days, but I cant seem to put it all together. I hooked up an electret mic into an opamp and gave output to my arduino ...
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Why is microphone + opAmp + Arduino circuit not working?

I followed the mic + op-Amp part of this schematic exactly using an Lm386 chip: https://randomskk.net/projects/lightstrip/schematic.pdf and sent the output from the op-amp into a pin on an Arduino ...
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Can I replace a PLL Charge Pump with an Active LPF?

Background I am using a MAX9382 phase frequency detector in a project. The application notes recommend using a charge pump on the output of the IC. In PLL applications there is an up and down line ...
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Switching op-amp gain resistances - how?

Given the following circuit: What is the component / circuit I should be using to switch the signal between each of the gain resistors? (the ⊠s in the schematic) The inputs ID0 to ID2 are TTL (...
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When is it an instrumentation amplifier (In-Amp) and not an operational amplifier (Op-Amp)?

I've seen a number of different configurations for instrumentation amplifiers, including 2 opamp versions. This is also one. But it's just a differential amplifier preceded by input buffers. ...
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Voltage controlled current source

Here is a circuit that seems to work pretty well for allowing a voltage to control a current of up to maybe two amps. It works on the falstad simulator (the triangle wave voltage input produces an ...
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Battery directly connected to input of unpowered opamp. Will the input current drain the battery?

Is it possible to hardwire battery to opamp input, considering that most of the time normal power on opamp will be off ? Battery positive wire is connected to non-inverting input of opamp workiing as ...
12k views

opamp without negative supply

I connected the V- pin to ground and the V+ pin to +5V. I then connected in+ to ground and in- to +5V. I expected Vout to be a low value near ground (0V) but I'm getting about +1.7V. Is this normal?
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Voltage controlled voltage source

I am designing a high powered LED driver controlled by a microcontroller. Now it would be very easy to make a constant current limiter so I don't burn out my LED. I have a bunch of LM317's and ...
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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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Scaling analog signal before ADC: A low cost, low pin and component count solution

Extending the question: Scaling Voltage for Arduino Analog In, Beyond Voltage Dividers Making a simple digital thermometer. Ideally, my circuit will only need a 3.3v supply. The sampling will be by a ...
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How Would I Nomalize Cable TV Volume Between Commercials and Programming

I have had it with commercials on cable TV being a lot louder than the program I happen to be watching. I have also had the reverse where the program switches scenes and you cannot make out what the ...
12k views

Relationship between PSRR and gain

Wikipedia says that power supply rejection ratio (PSRR) is the ratio of output noise referred to the input vs noise at the power supply: The PSRR is defined as the ratio of the change in supply ...
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Feedback Resistor and Capacitor in amplifier

What is a feedback resistor and capacitor? Why are they are used in amplifier circuits?
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Operation Amplifier with Transistor output

Is there a name for feedback amplifier topologies which include an opamp and transistor in the feed-forward path?. I need to design an amplifier with high bandwidth (almost 100 MHz) and high gain (50) ...
• 421
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Current Indicator

I want to turn an LED indicator on when current is flowing through a path. If there's no current the LED will be off, and when there's current, the LED would turn on. I've been experimenting with ...
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Can I replace LM358N with NE5532N dual op amp?

In this circuit LM358N 1MHz 32V dual op amp is used (+12V and -12V). The question is, can I simply replace it with NE5532N 10MHz +-22V dual op amp for up to 8MHz DDS signal source? Basically, this ...
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