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johnfin
Joined: 13 Feb 2007
Posts: 14
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 04 Mar 2007 3:28 741 Op-amp resistors |
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| How do I determine what values the 2 equal resistors should be for inverting a signal without gain. Also, should the ground of the 741 also have a resistor. I have seen some examples where that is called R3 and is equivilant to the parallel resistance of r1&r2.
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IanP
Joined: 05 Oct 2004
Posts: 6361
Helped: 1509
Location: West Coast
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johnfin
Joined: 13 Feb 2007
Posts: 14
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| 05 Mar 2007 3:21 741 Op-amp resistors |
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| I read the article and that section. Very crypic and not easy to inderstand. I could not find a starting point for a 1:1 inverting signal. I guess I could start with two 1K resistors.
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clairvoyant13
Joined: 10 Dec 2006
Posts: 60
Helped: 1
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| 05 Mar 2007 4:11 Re: 741 Op-amp resistors |
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I think you can use 1k and 1k, 10k and 10k - to - 100k and 100k.
Bye!!!
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sohailshahzad
Joined: 13 Jul 2006
Posts: 30
Helped: 2
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| 05 Mar 2007 6:31 Re: 741 Op-amp resistors |
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| Resistor selection depends upon your requirement. The formulas are avail which are used to find the value of resistence.
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vsmGuy
Joined: 26 Jun 2006
Posts: 445
Helped: 23
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| 05 Mar 2007 6:43 741 Op-amp resistors |
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Easiest way to choose is vakues whihc do not draw much current.
You must make sure that the assumptions of opamp (high i/p impedance) is followed.
Click on "Helped me" button if I helped you.
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johnfin
Joined: 13 Feb 2007
Posts: 14
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| 06 Mar 2007 14:00 Re: 741 Op-amp resistors |
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| The formulas are easy r2/r1 BUT knowing what they do is the problem. For plain inversion of the signal you want two of the same values for r1 and r2. Why use a resistor at all if the value will be 1. My signal is a 10ma modified square wave and I have tried two 1K resistors, and the output signal is not an inversion of the input signal. Also used r3(gnd) with a value of the parallel resistance of r1&r2 per the 741 spec sheet.
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vsmGuy
Joined: 26 Jun 2006
Posts: 445
Helped: 23
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| 07 Mar 2007 10:41 741 Op-amp resistors |
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A voltage follower can be BOTH inverting AND noninverting...
Have a go through Floyd...
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ender84567
Joined: 20 Jan 2007
Posts: 82
Helped: 7
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| 09 Mar 2007 1:01 741 Op-amp resistors |
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| what are you trying to do? in general a 741 sucks at pretty much everything, the only real use i've ever found for them is when i needed a transistor level model since this is available for the 741
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vsmGuy
Joined: 26 Jun 2006
Posts: 445
Helped: 23
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| 09 Mar 2007 2:18 741 Op-amp resistors |
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| That is true.. there are better and cheaper variants of 741
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