Electronics > Projects, Designs, and Technical Stuff
sallen key butterworth low pass filter
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MarkF:
If you want a LC Filter Design on-line calculator, I use this one.  Butterworth and Chebyshev series or shunt calculations.

   https://www-users.cs.york.ac.uk/~fisher/lcfilter/
soldar:
I do not know if it helps but I found this: https://consort3.wordpress.com/2018/06/10/4th-order-single-op-amp-low-pass-filter/
Conrad Hoffman:

--- Quote from: Benta on June 08, 2019, 10:11:45 pm ---
--- Quote from: Conrad Hoffman on June 08, 2019, 10:00:40 pm ---I wrote a calculator for it here- http://www.conradhoffman.com/chsw.htm fifth item down. The design gets some criticism, but I've built many and they work well. You'll want to sim it in LTSpice or similar. I believe the Bessel filter (at least this one) is defined more by phase shift, so you'll probably enter a lower frequency than the -3dB target. Click on Bessel then start with the 18 kHz and try an ISF of 0.0555 to get all 1000 pF caps.

--- End quote ---

Sorry, but .zip files turn me off.
Apart from that, please provide calculations about what you're postulating. "I believe the..." etc. doesn't really suffice.

--- End quote ---

Can't really help you then, but you can go to the source I used- Function Circuits: Design and Applications, 1976, part of the Burr-Brown electronics series. Out of print, but commonly available used.
Benta:
If you can't work without .zip files, fine, that's your karma.
But does the link provided by soldar represent the topology you're talking about?

Conrad Hoffman:

--- Quote from: Benta on June 09, 2019, 10:38:21 pm ---If you can't work without .zip files, fine, that's your karma.
But does the link provided by soldar represent the topology you're talking about?

--- End quote ---

Yes, same filter, but with his addition of damping. The reason I use the zip files is because I can't just put up an exe file. Well, I can, but most people couldn't (and shouldn't) download it. The math for the filter is unwieldy, so a numerical solution is used. Either way, it's not something you'd want to do by hand.
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