Output Voltage Determination in Op-Amp
Correct Answer: (c) Both positive and negative saturation voltage
Explanation:
The output voltage of an op-amp is primarily determined by both positive and negative saturation voltages, which define the limits of the output voltage range.
Saturation Voltages:
Positive Saturation Voltage (Vsat+):
Maximum positive output voltage the op-amp can deliver, typically around 1-2V below positive supply voltage (+Vs).
Vsat+ is approximately +Vs - 1.4V (for typical op-amp like 741 with ±15V supply)
Negative Saturation Voltage (Vsat-):
Maximum negative output voltage the op-amp can deliver, typically around 1-2V above negative supply voltage (-Vs).
Vsat- is approximately -Vs + 1.4V (for typical op-amp like 741 with ±15V supply)
Output Voltage Range:
The output voltage is limited to: Vsat- < Vout < Vsat+
For ±15V supply: approximately -13.6V < Vout < +13.6V
For single 5V supply: approximately 0V < Vout < +3.6V
Factors Affecting Output Voltage:
1. Saturation Voltages:
These define the absolute limits of output swing
Dependent on supply voltages and circuit design
2. Input Voltage Difference:
Vout = A(open-loop) × (V+ - V-)
For ideal op-amp in open loop: Vout reaches Vsat
3. Feedback Network:
In closed-loop: Vout = Af × Vin
Where Af is the feedback-determined gain
4. Load Current:
Affects output impedance and voltage drop
Relationship Between Factors:
The final output voltage is bounded by saturation voltages, which are determined by the supply voltage. The op-amp cannot exceed these limits regardless of the input signal.
Conclusion:
The output voltage of an op-amp is ultimately determined by both positive and negative saturation voltages, which set the maximum and minimum output limits. These saturation voltages depend on the supply voltage and op-amp design, and represent the boundaries within which the output voltage must operate.