Question

For the Op-Amp in the figure below find the magnityde of the output voitage Vout R. 100 kΩ Op-amp parameters +12 V AOL = 80,000 22 Mo Tout 75 0(maximum) Slew rate-8 V/μs Rin 100 kΩ in 16 Vpp RL -12 V

Answer 1

One of the properties of an ideal op amp is that it can drive any load. In other words, the ideal op amp will supply whatever output current is necessary to achieve the output voltage set by the input and the feedback network.

Consider the circuit with and without a load resistor. Without a load resistor (i.e. RL→∞) there is clearly only one path for the output current to flow -- into the feedback resistor, and this current also flows entirely into the input resistor since no current flows into an ideal op amp's inputs. This sets the relationship between the input and output voltages for the inverting amplifier. Adding a finite load resistance doesn't affect the feedback network nor the relationship between input and output -- it just means that the op amp needs to supply more output current (the usual current into the feedback network, as well as the current into the load resistor to satisfy Ohm's Law). Since an ideal op amp can output any current necessary, the load resistor does not affect the transfer function.