Question

Q1. You are given a 12 V DC power supply. You are expected to develop a voltage divider to achieve a voltage of nominal 5V value using a pair of resistors from the E 12 range, with the restrition that you are not expected to draw a current of more than 1 mA from the 12 V DC supply i. Develop a simple circuit showing the possible values for each resistor pair, and the range of the DC output possible due to 4 possible combinations of E 12 range of resistors. [Hint: Based on the restriction of less than 1 mA to be drawn from the power supply, calculate the values of nearest resistor pair values; and then calculate the resultant output voltage closest to 5 V]. Based on the selected case which gives you the output voltage value closest to 5V, apply the tolerance of E 12 and calculate the possible range of DC output value You are given a set of multimeters with the following characteristics to measure this output voltage ii. iii. . An ideal voltmeter with infinite resistance b. A voltmeter with 10 MQ internal resistance A voltmeter with 1 ΜΩ internal resistance C. d. A voltmeter with 100 k0 internal resistance Draw a circuit diagram for each case and estimate the voltage range expected for one of the selected resistor pairs in part (i). What does this tell you about selecting a good voltmeter? Q2. In Q1 we see the impact of resistor tolerances in building a resistor divider as well as using a practical voltmeter to measure that voltage Propose an op-amp buffer circuit that can be inserted between the resistive divider and your multimeter to cure the problem of meter loading. Draw the suggested circuit showing the connection of the multimeter and the op-amp circuit i. If you want to measure the voltages up to ±12 V DC what practical measures you should consider in building the above circuit. ii. If the multimeter used is an analogue type with an indicator movement, which requires a current of SO μΑ for full scale deflection, for a voltage measurement range of 15 V what resistor should be added in series with this moving coil. State your assumptions. ii. Figure below indicates a circuit usable for an analogue multimeter. The voltmeter measures the voltage V applied between the op-amps non-inverting terminal and the ground. Assuming that the coil produces full-scale deflection when the current passing through it is at 50 μΑ, find a suitable value for R for the meter to deflect fully at 15 V DC v. What is the input resistance of the op-amp based analogue voltmeter in part (il)? Q3 Figure below shows a utilizes a 10 kQ potentiometer to realize an adjustable gain amplifier. 10-k2 pot (1-x) to i. Derive an expression for the gain as a function of the potentiometer setting of x assuming that the op-amp is ideal. What is the range of gains possible? ii. Show how to add a fixed resistor so that the gain could be in the range of 1 to 21 V/V.What should be the value of the resistor to be added? Q4. Consider the op-amp circuit in Figure below. R, th Ri i. Give suitable name to this circuit as used in the recommended text book i. By application of superposition principle, derive an expression for the differential mode gain of the circuit. (show your calculation in a step by step mode). i Derive an expression for the common mode gain of the circuit, with a suitable diagram to assist your calculation. iv. What is the mathematical relationship for the resistors, to achieve a zero common mode gain?

Answer 1

the op amp de at A sso thatte beuoeen Loo Hence the đHaxene ipt Lg 94% terminal . Trus-the us tage at the fnvesting frput noue the artlied voHageU The corrent though R( can be determined as 19 SRR-500. 四飞30

les R2 2. Ry 2- R2R 피 U as haue haue R F R2tRy 2010 Co haue m IR 3