Question

Deisgn an op-amp circuit that will give you an output voltage from 5V to 0V. There must be a resistor where when the resistance is 3475 voltage is 5v and when the resitance is 10,000 the output votlage must be zero.

Answer 1

Answer:

One of the ways to accomplish this is to use the resistance as a part of Wheatstone bridge and op-amp in difference amplifier configuration. This circuit is shown below:

First about the bridge:

In the following circuit R1, R2 and R4 are fixed at 10K. R2 is the resistance that varies from 10K to 3475ohms.

When R2 is equal to 10000 ohms, the voltage Va and Vb are both 2.5V. Therefore the difference amplifier gives an output voltage equal to

Vout = (RF/R5) (Vb - Va) = 0V

When R2 is equal to 3475 ohms then Va = 2.5V but Vb changes to

Vb = 10K * 5/(10K + 3.475K) = 3.71 volts …………......using potential divider theorem

Therefore Vout = (RF/R5)*(3.71 - 2.5) = (RF/R5)*1.21 = 4.13*1.21 =5V

Hope this helps.