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Often in power supply schematics they use two diodes at the inputs of opamps:

schematic

simulate this circuit – Schematic created using CircuitLab

What's the purpose of having two diodes at opamp inputs?

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    \$\begingroup\$ Limit the input swing when the opamp bottoms out to speed up the recovery? \$\endgroup\$ – winny Nov 16 '19 at 11:36
  • \$\begingroup\$ @winny For poor old opamps? \$\endgroup\$ – ElectronSurf Nov 16 '19 at 11:39
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    \$\begingroup\$ Pretty much. Also, whoever did the schematic is not within his or hers right mind when negative voltages are pointing up and positives down and C13 is “103”. But sure, if you look at older application notes for opamps, you should be able to find your antiparallel diodes there. \$\endgroup\$ – winny Nov 16 '19 at 12:07
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It's because op-amps should have near 0 voltage difference between the inputs. The diodes are there so that a large voltage difference doesn't de-bias the input stage by causing the internal transistors to operate in non-linear modes. Sometimes those diodes are internal to the op-amp. Basically just input protection diodes.

That's one of the (many) reasons you don't want to use op-amps as comparators. Comparators will never have those diodes, while sometimes op-amp do have them, meaning that they will draw a lot of current and clamp when the input(s) swing.

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It's provide protection again positive spike whose voltage is more than opamp vcc and negative spike whose negative voltage more than -vcc of opamp

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    \$\begingroup\$ Not in this case. The diodes aren't connected to Vcc or Vcc-, or ground. \$\endgroup\$ – JRE Dec 12 '19 at 11:58

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