EE 321 Lab 5 Fall 2003EE321 – Lab 5Diodes, Part 2 — Rectifier CircuitsThe purpose of this laboratory is to investigate the use of diodes in rectifier circuits and tobuild precision rectifiers.Half Wave Rectifiers1. Construct the simple half-wave rectifier shown in Figure 1 (use a 1N4001 diode). Test itsoperation at 100 Hz for a range of input am plitudes, from to 20 V p-p down to 1 V p-p, bysuperimp osing the input and output waveforms on your scope. Describe your results, andsketch a sample waveform.vi5k Ω2. How well does the rectifier work at higher frequencies (keep the input at 1 V p-p)? Theundershoot that you observe at 100 kHz is caused by diode capacitance. Temporarily replacethe rectifier diode (large capacitance) with a 1N4148 switching diode (low C). This shouldreduce the switching transient.3. Replace the diode in your circuit with the ‘superdiode’ shown in Figure 2 (use the 1N4148switching diode). Repeat the above measurements, using a low input frequency (about100 Hz).Does this give better rectification, and why? Increase the signal frequency to about 2 kHz.What causes the delayed turn-on of the rectifier? (Hint: Look at the output of the op ampon the other trace.)iV5k Ω741 Vo4. Substitute a 411 op amp for the 741. Compare the behavior of the two rectifiers at 2 kHzfrequency. Why is the performance improved with the 411? (Hint: Look at the output of theop amp on the other trace.)1EE 321 Lab 5 Fall 2003Full Wave Rectifiers5. Construct the ”bridge” rectifier (Figure 3) using a transformer to float the signal generator(10-20 V p-p, 100 Hz) and the 1N4001 diodes. Be sure to connect diodes as shown. Use aload of 5 kΩ.vivOR− +L6. Verify that the output is full-wave rectified. Sketch the output waveform for a 3 V p-p input.What is the flat part of the output waveform caused by? (Hint: How much voltage Viisrequired to turn the diodes on?) Because the grounds of the signal generator and the outputare different, both the input and output can NOT be viewed at once. The voltage betweenthe positive side of the signal generator and rectifier ground is dificult to interpert.7. Place a 10 µF capacitor across the load resistance, being careful to observe the polarity ofthe electrolytic capacitor. The input signal should be 10 V p-p. Sketch the output waveformand compare to the waveform without the filter capacitor. Measure the average DC voltageand peak voltage. Explain the waveform. Why is this called ‘filtering’ the output?8. Measure the p-p ”ripple” on the output, both amplitude and frequency. How does the fre-quency compare to the input frequency? Compare the p-p ripple amplitude with its theoreticalvalue. (To measure the ripple, AC couple your oscilloscope.)2EE 321 Lab 5 Fall 2003Pre-Lab1. Consider the ‘superdiode’ shown in Figure 2. Sketch the waveforms you would expect at theoutput of the op-amp and the top of the resistor. Consider the following:• If Vois positive which way is current flowing in the load resistor? Where is the c urrentcoming from? Which way is current flowing in the diode? What voltage would youexpect at the output of the op-amp?• Do the same for Vonegative.2. Consider the ”bridge” rectifier of Figure 3.• Sketch the current path thru the diodes during each half-cycle (first when the sine inputis positive and then when it is negative). Indicate the voltage drop across each diodeand the resistor.• Reverse any one diode and draw the current paths and find voltages as above. Whatwould the result be if you did this in the lab?3. Consider the ’ripple’ voltage for a full wave rectifier as you will use in Part 8. There will bea 5 kΩ load and a 10 µf capacitor. First sketch a figure of the waveform as in Figure 3.30 inSedra and Smith with correct time and voltage scales (use Vi= 10 V p-p).Use three methods to find the ripple amplitude. Calculate a number for each method.(a) Use ∆v/∆t = i/C to find the voltage drop. Show that this gives a peak to peak ripplevoltage of iT/C where T is the period of the rectified signal.(b) Use V = Vpeake−t/τfor the voltage drop. Show that this gives a peak to peak ripplevoltage of Vpeak(1 − e−T/τ).(c) Use a formula in the book.Reduce the load resistance to 100 Ω, and find the ripple voltage by the three methods. Whichmake sense, and which