Lab 2 Operational Amplifier

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Victor Gregory
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1 Lab 2 Operational Amplifier Last Name: First Name: Student Number: Lab Section: Monday Tuesday Wednesday Thursday Friday TA Signature: Note: The Pre-Lab section must be completed prior to the lab session. Lab objectives o Introduction to LM741 OpAmp o digital-to-analog converter with OpAmp o Current Source controlled by voltage Equipment o Measurement tools (Oscilloscope, Digital multimeter), o DC and AC voltage sources, o Range of resistances. Pre Lab Mark: /2 Lab Mark: /8 Total: /10 Page 1 of 7 v.4 Oct 2014

2 Prelab 1. A dependent source is either a voltage or current source whose value is proportional to some other voltage or current in the circuit. There are four different kinds of dependent sources. In this lab, you will build a voltage dependent voltage source using an OpAmp. a. Using KCL, find the value of V o in terms of V in, R 1, and R 2. R2 R1 Vin Figure 1 b. For the circuit shown in Figure 2, find the values of V x and V o in terms of V s, R a, R b, R 1 and R 2. How does any change in the value of R L affect the value of V o and I? R1 R2 Vs Ra Vx Rb RL I Figure 2 c. Assuming the circuit shown in Figure 2 is equivalent to the one shown in Figure 3, write the appropriate term for the dependent voltage source and choose the right polarity. V O Figure 3 Page 2 of 7 v.4 Oct 2014

3 2. A digital-to-analog converter (DAC) is a unit whose input is an n-bit digital word and whose output is an analog signal proportional to the binary value of the digital input. One way to implement the DAC is by using an Op-Amp. a. For the circuit shown in Figure 4, find the value of V o in terms of V 1, V 2, R and R F. R/2 Rf R V2 Figure 4 b. For the special case of R F = R, complete Table 1. V 1 (V) V 2 (V) V o (V) Table 1 3. Op-Amps can be used as adders. The circuit shown in Figure 5 is an example of the application of an Op-Amp an adder. Find the value of V o in terms of V 1, V 2, V 3, R 1, R 2, R 3, R and K. V2 V3 R1 R2 R3 (K-1)R R Figure 5 Page 3 of 7 v.4 Oct 2014

4 4. To make a current source, an Op-Amp can be used to feed a circuit with a constant current. The current generated is independent from the load and changes with variation of the input voltage value. Figure 6 shows a current source that is controlled with voltage. Figure 6 The output current I L is independent from R L. The current flowing to the load varies based on the voltage of the source and R. Therefore, with changing the voltage, we can adjust the current flowing into our circuit. Page 4 of 7 v.4 Oct 2014

5 Lab work: (741 Op-Amp) 1. Consider the circuit shown in Figure 7. Find the value of in terms of V 1 and V 2. Figure 7 If R= 20 kω, determine V 1 and V 2 such that you get -10V, -2.5 V, and 7.5 V for and write the results in the table below. (Note: input voltages, V 1 or V 2 can only be 0V or 5V) V2 Simulate the circuit using MultiSim for the case of = 7.5V. Show the results to the TA. Build the circuit and measure the output voltage for the case of = 7.5V. Op-Amp supply voltages are ±15V. Show the output voltage to the TA. The pin out of op-amp 741 is shown below. 1 2 V V Consider the circuit shown in Figure 8. From your Pre-Lab calculations, you know the value of V o in terms of V 1, V 2. Page 5 of 7 v.4 Oct 2014

6 Figure 8 Assuming R = 100 kω, find and verify it by simulating the circuit using Multisim. Use a combination of DC and AC signals as inputs as listed below: v : 5 V DC v V2: Sine waveform 1 V (peak-to-peak) at 1 khz (AC) Show the TA the output voltage. Hint: In this example, output voltage (V o ) is a combination of AC voltage (1KHz) and DC voltage. So you should use the oscilloscope in simulation to see both DC and AC signals. Build the circuit you have simulated and draw the output waveform that you see on the screen of the oscilloscope. Indicate lt/div and Time/Div. and 0V (ground) line of the oscilloscope screen. lt/div (with unit) = Time/Div (with unit) = Op-Amp is also used to make a current source. Figure 9 shows an example of a current source. Page 6 of 7 v.4 Oct 2014

7 Figure 9 From the PreLab, you know the value of I! in term of V S. Using the values of V s, R L and R from the table below, find the output current I! in Figure 9. Simulate the circuit using MultiSim and measure the output current of OpAmp I! and write down the values in the table below. Build the circuit and measure the output voltage for each case. (Hint: to have Vs= 2.5V you can use a voltage divider with two equal resistors) V s R L (KΩ) R(KΩ) I calculated I simulated I measured V out measured Do you think that this current source is ideal? If not, describe the reason. Page 7 of 7 v.4 Oct 2014

Lab 3 Transient Response of RC & RL Circuits

Lab 3 Transient Response of RC & RL Circuits Last Name: First Name: Student Number: Lab Section: Monday Tuesday Wednesday Thursday Friday TA Signature: Note: The Pre-Lab section must be completed prior