# 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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### 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 ...
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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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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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### 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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### 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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### 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) ...
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1k views

### 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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### troubleshooting GEOFEX guitar effect panner

I'm building a circuit that allows me to blend a guitar effect in and out, based on >this< (page 2, bottom circuit). I have, however, replaced the 10k pot and the 15k and 51k resistors with 100k, ...
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### Difference between configurations of unity gain buffer using op-amp

Is there any practical difference as to how a unity gain buffer using an op-amp might be configured? For example, the input signal can be connected to the noninverting input and the feedback to the ...
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1 vote
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### Differential to single-ended conversion - transformer or instrumentation amp?

I need to convert the output of differential output DAC to single ended. It's a 2 Vpp signal with a 1 V common-mode output. The output is 100 ohms. Should I use a transformer or a instrumentation amp. ...
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### If I'm amplifying a triangle or square wave, does the GBWP of my op-amp need to be higher?

I want to amplify a 4 MHz triangle or square wave by 2 using an op-amp. Do I need an ~8 MHz op amp, or a much higher rated (and more expensive) device to handle the harmonics?
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### Which op-amp for audio?

I understand that the NE5532 is an evergreen in audio applications. Which other op-amps would you consider for preamp, filter and other high fidelity audio applications?
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### Op amp Adder circuit and positive voltages

Reading questions on converting negative voltages to positive ones it has left me with a question that I can't seem to work out. The circuit looks like this: But you only have the one going to the ...
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### 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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### Develop an OpAmp circuit to measure average voltages

With four different sensors, V1, V2 V3, and V4 I need to develope an operational amplifier circuit to measure average temperature with following specifications: The output voltage range of each ...
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### 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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### using an op amp in a battery powered circuit

I'd like to use a simple non-inverting amp circuit in a small project I am working on. The project is battery powered, so naturally the only voltage I have access to is 3.3v. My question is: how ...
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### Why does my op-amp swing randomly when the inputs are disconnected?

In Electronics class today we were using a TL081 op-amp. When I disconnected the inverting and noninverting inputs, the op-amp's output (driving an LED) started switching on and off rapidly. What ...
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### Regarding slew rates, what would be the minimum for amplifying audio using an op-amp?

Many, many choices. And this is just Microchip's offerings. I'm going to be amplifying by a maximum of 5x using an op-amp. So I choose an op-amp with a GBWP of 50 kHz * 5 = 250 kHz. That still leaves ...
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### Op-amp gain bandwidth product

I've had this question for a while. Assume you have an otherwise perfect op-amp with a gain-bandwidth product of 5 MHz. You input a signal of 50mVp-p and amplify it by 10x. This limits your bandwidth ...
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### Audio delay using discrete components

I would like to make a circuit that causes an audio delay using discrete components. I know I can do small phase shifts using an opamp, but I am looking for something in the millisecond or second ...
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### Drawing a comparator op-amp in Multisim

I'm attempting to draw the following two circuits up in NI Multisim 10, to attempt simulation and confirm my calculations. However, I'm not sure how to represent the Vin and Vout sources. Also, ...
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### Building a intermediate op-amp

I'd like to build a cheap and easy op-amp to use with my electric guitar. The op-amp should input from the guitar's jack and output to a standard "earphone's cable" jack ( not sure about the jargon ...
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