模拟电路实验.docx

1、模拟电路实验Project 1Power SuppliesObjective: This project will show some of the basic principles of power supplies using fullwave rectifier, Zener diode, and fixed-voltage regulator circuits.Components: Bridge Rectifier (50 PIV, 1 A), Zener diode (10 V at 500 mW), 7805 regulatorIntroduction:Most of the d

2、irect current (DC) power used in electronic devices is derived by converting 60 Hz, 115 V alternating current (AC) power to direct current power. This AC to DC conversion usually involves a step-down transformer, rectifier, filter, and a regulator. The step-down transformer is used to decrease the A

3、C line voltage from 115 VRMS to an RMS value near the DC voltage needed. The output of the step-down transformer is then fed into a diode rectifier circuit that only outputs positive halves of the input sinusoid. A filter is then used to smooth the rectifier output to achieve a nearly constant DC vo

4、ltage level. A regulator can be added after the filter to ensure a constant output voltage in spite of changes in load current and input voltages.Two different types of voltage regulators will be used in this project. The first involves a Zener diode circuit and the second involves a voltage regulat

5、or circuit. A Zener diode can be used as a voltage regulator when the diode is reverse biased and operated in the breakdown region. To maintain voltage regulation, the Zener diode must be operated in the breakdown region at a current greater than the knee current (IZK). For currents greater than IZK

6、, the Zener diode characteristic curve is nearly vertical and the voltage across the diode changes very little. Of course there is a maximum current the diode can tolerate, so good regulation is provided when the diode is reverse biased with currents between IZK and IZMAX. Zener diodes are available

7、 with a wide variety of breakdown voltages. Another type of voltage regulator is available with the 7800 series regulators. This series of fixed-voltage regulators is numbered 78xx, where xx corresponds to the value of the output voltage. Output voltages from 5 to 24 volts are available. These regul

8、ators are easy to use and work very well.Design:1. Find approximations for the DC voltage level and AC peak to peak ripple voltage for the bridge rectifier and filter circuit of Figure 1-1.2. For the Zener diode regulator circuit of Figure 1-2 assume that the Zener diode will regulate at 10 V over a

9、 current range of 5 mA to 25 mA. Assuming that the current flowing through R is always between 5 mA and 25 mA and the Zener diode is regulating at 10 V, find the minimum values of R and RL required. You may assume the forward diode drop for the two diodes is 1 V.Lab Procedure:1. Construct the bridge

10、 rectifier circuit of Figure 1-1 without the capacitor. Use the Variac with the step-down transformer for the input voltage to the bridge rectifier. With the transformer plugged into the Variac, adjust the Variac until the secondary voltage from the transformer equals 12 VRMS. BE CAREFUL not to shor

11、t the secondary terminals! Observe the secondary waveform on the oscilloscope. Put the oscilloscope on DC coupling and observe the load voltage waveform VL. Remember that both the input source and the load cannot share a common ground terminal.2. Remove power from the circuit. Insert the capacitor a

12、s shown in Figure 1-1 being sure to observe the correct polarity. Energize the circuit. With the oscilloscope on DC coupling observe VL. Measure the DC voltage level using the digital voltmeter. With the oscilloscope on AC coupling observe the ripple voltage VR. Compare these measured values with th

13、e calculated values.3. Observe the effect of loading on the circuit by changing the load resistor from 1 k to 500 . Measure the DC voltage level with the digital voltmeter. Observe the ripple voltage with the oscilloscope set on AC coupling. Compare these values with the previously recorded values.4

14、. Record the Zener diode characteristic curve from the digital curve tracer. Note the value of the breakdown voltage in the breakdown region. Also note the value of the knee current IZK.5. After verifying your designed values for R and RL with the instructor, construct the Zener diode regulator circ

15、uit of Figure 1-2. Measure the DC voltage level with the digital voltmeter for the minimum value of RL along with several values above and below the minimum value. Be careful not to overload the Zener diode. Comment on the circuits operation for these different load resistances.6. Construct the 7805

16、 regulator circuit of Figure 1-3 being careful to observe the correct pin configuration of the regulator. Measure the load voltage for RL equal to 300 , 200 , and 100 . Calculate the current for each of these cases. Does the value of the load resistor affect the output voltage?7. Using RL equal to 2

17、00 , record the 7805 regulator input voltage (pin 1) and output voltage (pin 3). Decrease the regulator input voltage by decreasing the setting of the Variac. For each decrease in amplitude, record the regulator input and output voltages. Continue decreasing the amplitude until the output of the reg

18、ulator drops a measurable amount below 5 V. What is the minimum input voltage needed for the 7805 regulator to produce a 5 V output?Questions:1. Why cant the input source and load have a common ground in the bridge rectifier circuit?2. Can the Zener diode be used as a conventional diode? Explain you

19、r answer and verify with a curve from the curve tracer.3. Would the value of the output filter capacitor have to increase, decrease, or remain the same to maintain the same ripple voltage if the bridge rectifier were changed to a half-wave rectifier? Explain your answer.4. How would increasing the f

20、requency of the input source affect the ripple voltage assuming all components remained the same?Project 2Analog Applications of the Operational AmplifierObjective: This project will demonstrate some of the analog applications of an operational amplifier through a summing circuit and a bandpass filt

21、er circuit.Components: 741 op-ampIntroduction:Figure 2-1 shows a weighted summer circuit in the inverting configuration. This circuit can be used to sum individual input signals with a variable gain for each signal. The virtual ground at the inverting input terminal of the op-amp keeps the input sig

22、nals isolated from each other. This isolation makes it possible for each input to be summed with a different gain.The bandpass filter shown in Figure 2-2 uses an op-amp in combination with resistors and capacitors. Since the op-amp can increase the gain of the filter, the filter is classified as an

23、active filter. This bandpass filter circuit is extremely useful because the center frequency can be changed by varying a resistor instead of changing the values of the capacitors. The center frequency is given by:The center frequency can be changed by varying the variable resistor R3. Increasing R3

24、decreases the center frequency while decreasing R3 increases the center frequency. The bandwidth is given by:Notice that the bandwidth is independent of the variable resistor R3 so the center frequency may be varied without changing the value of the bandwidth. The gain at the center frequency of the

25、 bandpass filter is given by:Design:1. Find the relationship between the output and inputs for the weighted summer circuit of Figure 2-1.2. Design a bandpass filter with a center frequency of 2.0 kHz and a bandwidth of 200 Hz. Let the voltage gain at the center frequency be 20. Check your design wit

26、h PSPICE. Use 15 V supplies for the op-amp. Use RL = 2.4 k.Figure 2 - 1: Weighted SummerFigure 2 - 2: Bandpass FilterLab Procedure:1. Construct the summing amplifier of Figure 2-1. Design for the transfer function to be VO = -2 VIN1 - VIN2. Use 15 V supplies for the op-amp. Use RL = 2.4 k.2. Let VIN

27、1 be a 1 V peak sine wave at 1 kHz and VIN2 equal to 5 V DC. Verify the amplifiers operation by monitoring the output waveform on the oscilloscope.3. Construct the bandpass filter of Figure 2-2. Use the designed values for the resistors and capacitors. Use 15 V supplies for the op-amp. Use RL = 2.4

28、k.4. Record and plot the frequency response (you may want to use computer control for the sweep and data collection). Find the center frequency, corner frequencies, bandwidth, and center frequency voltage gain to verify that the specifications have been met.5. Change R3 to lower the center frequency

29、 from 2.0 kHz to 1.0 kHz. Repeat part 4 for the new frequency response. Verify that the new center frequency is 1.0 kHz. What is the new bandwidth? What is the new center frequency voltage gain? Compare with the measurements of Procedure 4.Questions:1. Could the summer circuit be used with the input

30、s connected to the noninverting terminal and produce the same affect without the inversion? Explain.2. What is/are the benefit(s) of using an op-amp circuit to produce a bandpass filter over using an RLC circuit with a noninverting op-amp at the output of the RLC circuit?Project 3Analog Computer App

31、lications using the Operational AmplifierObjective: This project will focus on the use of the operational amplifier in performing the mathematical operations of integration and differentiation. The design of a simple circuit (analog computer) to solve a differential equation will also be included.Co

32、mponents: 741 op-ampIntroduction:Figures 3-1 and 3-2 illustrate two op-amp based circuits designed to perform differentiation and integration respectively. The operations are performed real-time and can be helpful in observing both initial transients and steady state response. The analysis of the circuits is based on the ideal op-amp assumptions and performed in the time domain. The resistor RI shown in the two circuits is included to help with stability and for general circuit protection. The value for RI is nominally set e