# Amplifier Circuits

## Main Question or Discussion Point

Hi

Does anybody have any useful material on how to calculate unknown voltages in an amplifier circuit.

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Baluncore
2019 Award
Does anybody have any useful material on how to calculate unknown voltages in an amplifier circuit.
Yes. But there are many different types of circuits. It is best to attach a picture or post a link to the actual circuit.
We can then show you how to find the unknown voltage.

Yes. But there are many different types of circuits. It is best to attach a picture or post a link to the actual circuit.
We can then show you how to find the unknown voltage.
Here are the circuit examples. Thanks

#### Attachments

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CWatters
Homework Helper
Gold Member
Hints for circuit a)....
There is an input current specified.
For the op amp to be operating in a linear mode what must the voltage be on the -ve input?
If the input impedance of the opamp is high, where does the input current go?

Hints for circuit a)....
There is an input current specified.
For the op amp to be operating in a linear mode what must the voltage be on the -ve input?
If the input impedance of the opamp is high, where does the input current go?
Hi Thanks for the reply. I am just starting out with learning about these circuits so my original question was does anybody have any material that can help me understand how to calculate unknown voltages in these types of circuits. The image is an example of what im working towards solving. The hints are much appreciated though.

Baluncore
2019 Award
You need to know that ...
An op-amp output voltage rises if input(+) is greater than input(–).
The op-amp output voltage falls if input(+) is lower than input(–).
That means that when input(+) is equal to input(–) the output will be stable.

Currents flowing through resistors drop voltages. Ohms law. V = I * R.
Chains of resistors form potential dividers.

Start here with op-amp circuits.
https://en.wikipedia.org/wiki/Operational_amplifier_applications#Amplifiers

• Enochfoul
analogdesign
Hi Enochfoul,

MIT has received permission to provide a older edition of "Op Amps for Everyone", which is Texas Instruments' stellar and easy-to-follow introduction to op amps. It covers almost everything you would need to know about op amps to become an expert, and will be really helpful in solving the kinds of problems you showed and can expect to encounter.

http://web.mit.edu/6.101/www/reference/op_amps_everyone.pdf

• jim hardy, davenn and Enochfoul
Thanks for all of your help.

jim hardy
Gold Member
2019 Award
Dearly Missed
• davenn
Thank you for all of the information there is a lot of it! I am still trying to figure out how to calculate the unknown voltages and I have looked everywhere for a worked example to show how to calcualte the unknowns. It is probably staring me right in the face in the materials you have given me! Does anybody have a worked example of a how to find these unknown voltages? I am a bit overwhelmed by the amount of information out there.

Baluncore