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Old 23rd January 2005, 06:52 PM   #1
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Default High/Low-Pass filter calculations

Im planning to build some active filters. Searching the web came up with the perfect document - The SLOA093 ap note from TI on active filter design. One simple question. What units do the calculations use? Farads and Ohms right? I dont want to buy components 1,000,000 time too large. :P
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Old 23rd January 2005, 08:01 PM   #2
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Default Re: High/Low-Pass filter calculations

Quote:
Originally posted by Matttcattt
What units do the calculations use? Farads and Ohms right? I dont want to buy components 1,000,000 time too large. :P
I think it assumes just Farads and Ohms. Of course you can enter Millifarads, but be sure to treat the result as Milliohms
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Old 23rd January 2005, 09:53 PM   #3
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Thanks. I just wanted to get a second opinion.
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Old 23rd January 2005, 10:24 PM   #4
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Default Filter Calcs

Hi Matttcattt
The calculations are intended for basic units ie. ohms, farads and hertz. Just use the appropriate multiplier when entering your component values.
Eg. 100 pF = 100 x 10 to -12 power, 0.1 mF = 0.1 x 10 to -6 power, 1k ohm = 1 x 10 to +3 power, 10 KHz = 10 x 10 to +3 power. You get the idea?
Hope this helps.
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Rob
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Old 24th January 2005, 10:55 PM   #5
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Thanks.

I dont like standard form (1x10^-6F). I prefer long decimals (0.000001F).
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Old 24th January 2005, 11:04 PM   #6
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You could try the sim on National's website, Webbench, it uses real world values.
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Old 25th January 2005, 10:17 PM   #7
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TI also has a rather powerful program called FilterPro that will automate much of this for active filters. You can choose topology and choose some components while allow the rest to be auto-selected. I'd check it out.
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Old 26th January 2005, 04:28 AM   #8
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Quote:
Originally posted by Evan Shultz
TI also has a rather powerful program called FilterPro that will automate much of this for active filters. You can choose topology and choose some components while allow the rest to be auto-selected. I'd check it out.
I agree, simple and easy to work with.

Here is the link: http://www-s.ti.com/sc/techzip/slvc003.zip
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Old 26th January 2005, 06:38 PM   #9
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I've already calculated the values and ordered the parts now, but I'll have a look anyway.
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