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Subject: Re: OP Amp Output Resistance
Date: Wed, 25 Sep 2002 14:19:05 -0700
Organization: Ye 'Ol Disorganized NNTPCache groupie
NNTP-Posting-Date: Wed, 25 Sep 2002 21:16:14 +0000 (UTC)
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Bob Wilson wrote:
>In article <3D8D30C9.email@example.com>,
>>All op amps have a non zero output resistance that is not noticable due
>>to feedback unless varying current demand exceeds the bandwidth of the
>>amplifer. I need to know how linear this resistance is.
>>I also would like to know if the output resistance is not specified, if
>>it can be deduced by how output voltage swing specification varies with
>Yes. Varying your load resistance and noting the results will certainly
>allow you to determine what the source resistance is, whether it is an
>opamp or anything else.
Can it be assumed the output resistance is the same or roughly the same
near the power supply rails as it would be near the center of the output
It is the linearity of the open loop output resistance with DC output current I
most want to know about. But there is some interest in how this changes with
frequency of current demand as well. Thanks Glenn for the reference to the spec
sheets for the AD811 and AD712. But the Fig 8 on page 5 of the AD811 spec is
closed loop output resistance. TPC 6 on page 4 of the AD712 spec does not say if
the output resistance is closed or open loop.
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