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Electronics => Projects, Designs, and Technical Stuff => Topic started by: raff5184 on February 27, 2017, 11:25:24 pm

Title: op amp feedback values
Post by: raff5184 on February 27, 2017, 11:25:24 pm
Hi I am building this evaluation board: http://www.analog.com/media/en/technical-documentation/user-guides/UG-755.pdf (http://www.analog.com/media/en/technical-documentation/user-guides/UG-755.pdf)

How do I design CF  and CL in the fist circuit on page 3? Is there a formula?
Thank you
Title: Re: op amp feedback values
Post by: tpowell1830 on February 28, 2017, 01:37:16 am
It depends on how you want to use the Op Amp. if you are just using as an Op amp with gain, you don;t really need Cf and CL. How do you plan to use it? If you want to create an oscillator, there is one formula and if you just want to amplify a signal there is another. Did you get any other info with the device? I don;t see the specs. Look at Dave's video on setting Op amp gains etc or this one from w2aew that I like.

https://www.youtube.com/watch?v=K03Rom3Cs28 (https://www.youtube.com/watch?v=K03Rom3Cs28)
Title: Re: op amp feedback values
Post by: danadak on February 28, 2017, 02:23:41 am
This might help -


http://www.ti.com/lit/an/sloa020a/sloa020a.pdf (http://www.ti.com/lit/an/sloa020a/sloa020a.pdf)


Regards, Dana.
Title: Re: op amp feedback values
Post by: raff5184 on February 28, 2017, 03:03:48 am
I just plan to use it as a power amplifier, to increase the input voltage or power in general.
I found the formula CL= 1/(2*pi*R*f) , but apparently I don't need it since, if I am correct, CL is used to create a low-pass filter(?)
Title: Re: op amp feedback values
Post by: tpowell1830 on February 28, 2017, 03:12:28 am
Quote from: raff5184 on February 28, 2017, 03:03:48 am
I just plan to use it as a power amplifier, to increase the input voltage or power in general.
I found the formula CL= 1/(2*pi*R*f) , but apparently I don't need it since, if I am correct, CL is used to create a low-pass filter(?)

Yes, a low pass filter. I think that the drawing is showing that all of those features are available on the board, but you don't necessarily need them. If you want to create a high gain amplifier, there is a method to choosing the components and you can do it with a much smaller component count than is shown.