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i was reading on the unity buffer amplifier. I did understand, that it can help provide extra current that source might not be able to provide. But where does this current come from?

Is it from the External power supply to the opamp?

If Yes, does that mean we should keep a different power supply for both the opamp and the source?

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Yes, the current comes from the opamp's power supply.

As long as the power supply has enough current capacity for both the source and the opamp, it can be use for both.

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  • \$\begingroup\$ As far as I understand opamps are only voltage boosting devices, how they supply current? \$\endgroup\$ – AKR Sep 7 '13 at 3:27
  • \$\begingroup\$ @AKR: Your understanding is incorrect. The output stage of an opamp is a voltage source. This means that it has an arbitrarily low output impedance (depending on the implementation technology) and can supply an arbitrary amount of current, which is drawn from its power supply. \$\endgroup\$ – Dave Tweed Sep 7 '13 at 3:41
  • \$\begingroup\$ Do we have some range of this arbitrary current? \$\endgroup\$ – AKR Sep 7 '13 at 3:44
  • \$\begingroup\$ @AKR: Look at the datasheet for your opamp. \$\endgroup\$ – Dave Tweed Sep 7 '13 at 3:49
  • \$\begingroup\$ Look at the datasheet, but 5ma or 20ma or sometimes 50ma would be typical values. \$\endgroup\$ – Brian Drummond Sep 7 '13 at 10:33

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