Mar 12, 2020 #1 chandlerbing65nm Member level 5 Joined Apr 5, 2018 Messages 80 Helped 0 Reputation 0 Reaction score 1 Trophy points 8 Activity points 709 Hi folks, I am just curious about the op amp test circuit of analog devices, why is the feed back loop connected to the positive input of the DUT, knowing that positive feedbacks are unstable and saturates the ouput. Kindly refer to this article by analog devices. https://www.analog.com/en/analog-dialogue/articles/simple-op-amp-measurements.html#
Hi folks, I am just curious about the op amp test circuit of analog devices, why is the feed back loop connected to the positive input of the DUT, knowing that positive feedbacks are unstable and saturates the ouput. Kindly refer to this article by analog devices. https://www.analog.com/en/analog-dialogue/articles/simple-op-amp-measurements.html#
Mar 12, 2020 #2 D dick_freebird Advanced Member level 7 Joined Mar 4, 2008 Messages 8,956 Helped 2,333 Reputation 4,683 Reaction score 2,511 Trophy points 1,393 Location USA Activity points 71,375 Because in the classical servo measurement loop the integrator (auxiliary amplifier) provides the inversion.
Because in the classical servo measurement loop the integrator (auxiliary amplifier) provides the inversion.
Mar 13, 2020 #3 chandlerbing65nm Member level 5 Joined Apr 5, 2018 Messages 80 Helped 0 Reputation 0 Reaction score 1 Trophy points 8 Activity points 709 But what is the purpose of connecting the feedback at the positive input, rather than the negative input.
But what is the purpose of connecting the feedback at the positive input, rather than the negative input.
Mar 13, 2020 #4 S sutapanaki Advanced Member level 4 Joined Nov 2, 2001 Messages 1,346 Helped 523 Reputation 1,048 Reaction score 486 Trophy points 1,363 Location US Activity points 11,152 If you connect the feedback to the negative input you will end up having a positive feedback. That's the purpose.
If you connect the feedback to the negative input you will end up having a positive feedback. That's the purpose.
Mar 13, 2020 #5 E Easy peasy Advanced Member level 6 Joined Aug 15, 2015 Messages 4,746 Helped 1,402 Reputation 2,804 Reaction score 1,933 Trophy points 1,393 Location Melbourne Activity points 26,219 you need to look at the WHOLE circuit - not just the op-amp bit ...
Mar 14, 2020 #6 Ata_sa16 Full Member level 6 Joined Mar 29, 2016 Messages 343 Helped 59 Reputation 118 Reaction score 58 Trophy points 28 Location Milky Way Galaxy, 179° 56′ 39.4″ Activity points 2,221 The way to test this is easy Imagine TP1 rises 1) V+ of DUT will increase 2) output of DUT will increase 3) V- of Aux opamp will increase 4) TP1 will drop Therefore the loop is negetive feedback and stable Now assume you connect to negetive input 1) V- of DUT will increase 2) output of DUT will decrease 3) V- of Aux opamp will decrease 4) TP1 will increase further ... positive feedback !
The way to test this is easy Imagine TP1 rises 1) V+ of DUT will increase 2) output of DUT will increase 3) V- of Aux opamp will increase 4) TP1 will drop Therefore the loop is negetive feedback and stable Now assume you connect to negetive input 1) V- of DUT will increase 2) output of DUT will decrease 3) V- of Aux opamp will decrease 4) TP1 will increase further ... positive feedback !