If the circuit values are as specified, what is Vo?

If the circuit values are as specified, what is Vo?

• A. -12 Vdc
• B. 12 Vdc
• C. 0 Vdc
• D. -6 Vdc

Answer: (A)

When an op-amp is used with feedback, it tries to drive its inputs to be equal. But the output can only swing between its supply rails. If the required output to satisfy the feedback would be more negative than the negative supply allows, the amplifier saturates at that negative rail. In this circuit, the specified values push the output toward the negative rail, so Vo ends up at the negative supply level, which is -12 Vdc. The other options would require either a balanced zero output, a positive swing, or a non-rail-limited level, none of which occur because the circuit is limited by the negative supply.

When an op-amp is used with feedback, it tries to drive its inputs to be equal. But the output can only swing between its supply rails. If the required output to satisfy the feedback would be more negative than the negative supply allows, the amplifier saturates at that negative rail. In this circuit, the specified values push the output toward the negative rail, so Vo ends up at the negative supply level, which is -12 Vdc. The other options would require either a balanced zero output, a positive swing, or a non-rail-limited level, none of which occur because the circuit is limited by the negative supply.