# OP-Amp Circuit Design

1. ## OP-Amp Circuit Design

In class, we were asked to design an amplifier with a given output of 3V using op amps. The output remains the same irrespective of the voltage at the input. I really need assistance getting through this.

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2. ## Re: OP-Amp Circuit Design

Hi,

I assume the input can be under or over 3V. You need to provide more/all the information for anyone to offer a useful answer. Joke: Show a mechanic a photo of your car's front left wheel and ask them why the car won't start... :)

I couldn't answer your question, however, what comes to mind is possibly a circuit that includes an error amplifier at the output end to maintain the output at 3V.

3. ## Re: OP-Amp Circuit Design

you need to state the entire specification
you stated the output
what is the input? is it AC or DC?
if it is AC, what frequency range?
since it is an amplifier, what is the required gain?
what voltage are you using to power the op-amp?

you need to show what you did.
schematic at a minimum (with parts clearly labeled)
the calculations you did for the circuit
simulations if you have them

the more complete the information, the more likely
you'll get useful help

since it is an op amp circuit, look at this:
https://archive.org/details/National...k1994/mode/2up

its the National Semiconductor Linear applications Handbook
I had one on my shelf for years.

or this
Handbook of Operational Amplifier Applications from Texas Instruments
it is a pdf

1 members found this post helpful.

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4. ## Re: OP-Amp Circuit Design

The output remains the same irrespective of the voltage at the input
Are you really sure it's an amplifier you need?
Or are you asking for the output to be accurately scaled up from the voltage at the input?
Or are you asking for an ALC design that takes different signal levels in and tries to give a fixed level out?

Brian.

5. ## Re: OP-Amp Circuit Design

Hi,

Yes, it's a riddle.

And I guess, that with "voltage at the input" you mean "supply voltage".

An Opamp has two inputs. Thus - if you don't give additional information - we usually understand "Opamp input voltage" as the differential input voltage.

Klaus

6. ## Re: OP-Amp Circuit Design

I think you just have to proof to have understood the various basic op-amp topologies. If so you have design a simple circuit that make the difference between to voltages and connect the 2 inputs togheter. In this case V1=V2=Vin so that Vo=V2-V1=0 regardless the input voltage Vin. Now you just have to add a 3V generator in series with the resistor between non-inverting input and ground. In this case you'll have a fixed 3V in output independently from the Vin level.
You should be able to generate the schematic by youself.
How the circuit works can be easily proven appling the ideal amplifier rules and the superposition theorem.

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7. ## Re: OP-Amp Circuit Design

Stupid assignment, IMO.

You could just cascade several high gain rail-to-rail opamps, open-loop, connect the power supply to 3V, and VOILA! always 3V out for all positive inputs.

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