Question

A voltage amplifier with an input resistance of 20 kohms, an ouput resistance of 100 ohms, and a gain of 1000 V/V is connected between a 100 kohm source with an open circuit voltage of 10 mV and a 100 ohm load. For this situation:

(a) What output voltage results?

(b) What is the voltage gain from source to load?

(c) What is the voltage gain from the amplifier input to the load?

(d) If the output voltage across the load is twice that needed and there are signs of internal amplifier overload, suggest the location and value of a single resistor that would produce the desired output.

Answer 1

(a) Vo = 833.3 mV

(b) Vo/Vs = 83.3 V/V

(c) Vo/Vi = 500 V/V

(d) Ri = 5 kOhm

Step-by-step explanation:

Vo = 10 x (20/(20+100))x 1000 x (100/100+100)

Vo = 833.3 mV

Vo/Vs = 833.3/10

Vo/Vs = 83.3 V/V

Vo/Vi = 1000x (100/100+100)

Vo/Vi = 500 V/V

Let Ri is the desired Resistance

RpIIRi = Rs/21

RpIIRs = 4.76

100Ri/(100+Ri) = 4.76

95.24Ri= 476

Ri = 5 kOhm