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According to the author of this schematic the bias currents will not flow without a power supply-input signal common ground. I don't understand why the bias currents wouldn't just flow into the negative terminals of the voltage source even without a dedicated ground.

I would be really grateful for any pointers.

enter image description here

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    \$\begingroup\$ Currents always flow in loops. why the bias currents wouldn't just flow into the negative terminals of the voltage source Where would you then connect the negative terminal of the voltage source? I suggest that you draw this (start on paper) and see if there is a loop where the bias current can flow. If there is no loop, the current cannot flow. \$\endgroup\$ Dec 15 '20 at 16:02
  • \$\begingroup\$ How many opamps have you seen with a +V pin, -V pin, and a GND pin? where the GND is actually involved with the analog pins (not auxiliary digital functions)? \$\endgroup\$
    – DKNguyen
    Dec 15 '20 at 16:15
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I don't understand why the bias currents wouldn't just flow into the negative terminals of the voltage source even without a dedicated ground.

They would. They will find a way to flow (out of the bases) into a more negative voltage whether it be ground (0 volts) or the negative rail or somewhere slightly more negative that the common-emitter point of the transistors.

If there is no connection to the bases or, the connection is to a voltage higher than the common emitter node, then bias currents (for this particular op-amp you sketched) won't flow.

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  • \$\begingroup\$ Thank you for the answer again Andy. Two questions in one day! Sorry I'm taking of your time, but this is all very confusing at times! \$\endgroup\$ Dec 15 '20 at 17:55
  • \$\begingroup\$ No problem @ZhelyazkoGrudov \$\endgroup\$
    – Andy aka
    Dec 15 '20 at 18:03

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