Question

Consider an op-amp connected in an inverting configuration to realize a closed-loop gain of -100 V/V utilizing resistors of 1k and 100 k. A load resistance RLis connected from the output to ground, and a low-frequency sine-wave signal of peak amplitude Vpeakis applied to the input. Let the op amp be ideal except that its output voltage saturates at 10 Vand its output current is limited to the range of 20 mA.

1) For RL = 1k, what is the maximum possible value of Vpeak while an undistorted output sinusoid is obtained?

2) Repeat A for RL = 200.

3) If it is desired to obtain an output sinusoid of 10 V peak amplitude, what minimum value of RL is allowed?

Answer 1

The op-amp circuit diagram is as shown below.

Part 1) RL = 1kOhm

When RL = 1kOhm, maximum possible output current =

Hence, RL cannot load opamp upto its 20mA output current rating.

Vpeak is limited by the output voltage saturation limit and op-amp closed-loop gain

Part 2) When RL = 200 Ohm, maximum possible output current

The op-amp output current must be limited to 20 mA. Therefore, maximum allowed output voltage peak

= 200 Ohm X 20 mA = 4 V.

Therefore, the maximum possible value of Vpeak while an undistorted output sinusoid is obtained is

Part 3) If it is desired to obtain an output sinusoid of 10 V peak amplitude, minimum value of RL is