BME/ISE 3512 Laboratory - Three Diode (1N4001)

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1 BME/ISE 3512 Laboratory Three Diode (1N4001) Learning Objectives: Understand the concept of PN junction diodes, their application as rectifiers, the nature and application of halfwave and fullwave rectifiers, operation of light emitting diodes (LEDs). Laboratory Equipment: NI mydaq Multimeter Supplies and Components: Breadboard 270 Resistor 27 Resistor 1 K Resistor 10 K Resistor 1 F Capacitor Diode 1N4001 (4 each) LED PreLab Questions 1. Discuss the basic operation of a solid state diode. Draw the VI curve for diode. List the forward barrier voltage for germanium and silicon PN junctions. 2. What are the differences between conductors, nonconductors (insulators) and semiconductors? Give an example of each. What category is germanium? 3. For a sine wave input, sketch the output wave form for both a halfwave rectifier, a fullwave rectifier, and full wave rectifier with coupling capacitor. PostLab Questions 1. List several practical uses of diode rectifiers. 2. Explain the operation of a LED. 3. What is the purpose of the series resistor? What circuit parameters determine its value? 4. What are photodiodes? What are the main differences between LEDs and photodiodes?

2 Laboratory Three Diode (1N4001) Laboratory Procedures 1) Measurement of VI curve of the pn junction of a silicon diode (1N4001). Figure 1. Circuit for measuring VI curve a) Build the circuit as shown in Figure 1. The power source is variable. R is used to limit the current passing through the diode (I < 15 ma). The current I is measured using a Multimeter. The voltage across the diode is measured using another multimeter (or an oscilloscope). b) Adjust Vs (the voltage supply) to obtain the value of V as shown in the table below, and record the I at each value of V. V I

3 2) Halfwave rectifier 1N4001 Sine Wave 100 Hz 2 V pp V in R 10 K + V out Figure 2. Circuit of halfwave rectifier In this experiment, a 100 Hz, 2 Vpp sine wave (Vin) is obtained from the Function Generator. In addition to being connected to the diode as shown in Figure 2, Vin is also connected to Channel 0 (AI0+ and AI0 ). Vout, obtained from R, is connected to Channel 1 (AI1+ and AI1 ). Adjust the xaxis or timebase to display 23 cycles of Vin and Vout. Record the voltage measurements for Vin and Vout. Save the data file to plot using Microsoft Excel or Matlab.

4 3) Fullwave bridge rectifier In this experiment, use 4 diodes to build a circuit as shown in Figure 3. Pay special attention to the connections of the 4 diodes that form a ring. Instead of using a transformer, use the function generator of the mydaq to generate a 10 Vpp, 60 Hertz Sine Wave. View the Output signal using the oscilloscope. Adjust the timebase so that 2 3 cycles are displayed on the screen. Save the output signal to be plotted later. 110 V power V in + R 10 K V out Figure 3. Circuit of fullwave rectifier

5 4) Fullwave rectifier with a capacitor for smoothing output. 110 V power V in 1N R 10 K C V out Figure 4. Circuit of fullwave rectifier with a smooth output The circuit for this experiment is almost the same as in Figure 3. The only difference is to add a capacitor of 1 F in parallel with R. Observe the waveform of Vout and compare with that in Figure 3. Try using a larger C (10 F), how does the output change? What is the role of C? Save both waveforms.

6 5) LED (Light Emitting Diode) Just like a diode, an LED also only allows current to pass in one direction. However, an LED is different from an ordinary diode in two aspects. First of all, an LED emits either visible or infrared light when a current passes through it. Second, its VI relation is significantly different than that of an ordinary diode: the voltage drop across the two terminals is much larger than 0.7V. In digital logic circuits, LEDs are usually connected to certain points in the circuit to provide a visible indication of the logic state: 0V (LED if OFF) for logic 0, +5V (LED is ON) for logic 1. According to the manufacture s spec sheets, each LED should be operated at a certain current (20 30 ma) and a certain voltage (3 4 V). In practice, one only needs to make sure that the current passing though the LED does not exceed a limit (e.g. 25 ma). Do not directly connect an LED to a voltage source that is higher than 4.5 V (the LED will be burned!). a) Build the circuit shown in Figure 5 and measure the current I and voltage VLED using a multimeter. b) Based on your measurement, determine the value of R so that I = 10 ma when a power supply is VCC (may be other than 5V). Hint: I = (VCC VLED)/R c) Test your design by performing another measurement using the circuit in Figure 5. In this case, the power supply is 10 V and a new R is used based on your calculation. Measure I and VLED for the new circuit. Multimeter to measure current A + I 5V + R = 270 LED + V LED Figure 5. A test circuit for LED

7 Grading Rubric: Diode 1N4001 (Lab 4) Name: Points Cover Page / 2 I) Introduction Discuss the following principles of a Diode: What are the typical doping agents for ntype and ptype silicon? How does each doping agent bond with silicon? What is a hole in ptype silicon? / 10 What are forwardbiasing and reversebiasing? What is a forwardbarrier voltage? Explain how this makes a diode, in effect, a voltagesensitive switch. II) Circuit Diagrams (Circuit Maker Only) 1) Experiment 1 Measure the VI Curve of 1N4001 Diode / 4 Resistor should be labeled with its measured value! For the ammeter, you can choose to either: a) include an ammeter in your circuit diagram, or b) simply note the direction of the current (I). Also be sure to label the part number of the diode (1N4001). 2) Experiment 2 HalfWave Rectifier / 4 3) Experiment 3 FullWave Bridge Rectifier / 4 For the stepdown transformer, there s actually a symbol in Circuit Maker called Transformer. You can search for transformer to find it. There s also a fullwave rectifier bridge; the symbol is called FW Bridge. 4) Experiment 4 FullWave Bridge Rectifier w/ Smoothing Capacitor / 4 Here, you only need one circuit diagram; indicate that two different capacitors (1μF and 10 μf) were used. 5) Experiment 5 LED / 4 There is an LED in Circuit Maker, too, under Diodes. Again, either include the ammeter in your circuit diagram, or simply indicate the direction of the current. III) Data and Results 1) Experiment 1 Measure VI Curve of 1N4001 Diode a. Measured Values of R / 2 b. Data Table for Values of V and I / 5 c. Graph of VI Curve from Experimental Data / 5 2) Experiment 2 HalfWave Rectifier a. Measured Value of R / 2 b. Graph of V OUT vs. Time / 5 3) Experiment 3 FullWave Rectifier a. Graph of V OUT vs. Time / 5 4) Experiment 4 FullWave Rectifier with Smoothing Capacitor a. Graph of V OUT vs. Time Using 1 μf Capacitor / 5 b. Graph of V OUT vs. Time Using 10 μf Capacitor / 5 5) Experiment 5 LED a. Measured Value for V LED, I, and R for both 5V and 10V / 6 b. Show the calculations for the resistor when the current is 10 ma / 4 IV) Discussion 1) Experiment 1 Measure the VI Curve of 1N4001 a) From the VI curve, can you identify (approximately) the forward barrier (bias) / 5 voltage? How did you identify where it is on the graph? 2) Experiment 2 HalfWave Rectifier a) Why is the negative part of the sine wave clipped? What property of the / 5 diode causes this?

8 3) Experiments 3 and 4 Full Wave Rectifier a) Plot all three output voltages (using no capacitor, the 1 μf capacitor and the 10 μf) on one graph (don t use the timeaxis data in this graph, since the three experiements weren t performed simultaneously; label the xaxis as Samples [n] ). Since the experiments weren t performed simultaneously, the peaks of the / 5 waveforms won t be aligned. However, you should be able to see the effects of the capacitor; explain what the capacitor does to the output signal. Why is this useful? V) PostLab Questions a) PostLab Question #1 / 2 b) PostLab Question #2 / 2 c) PostLab Question #3 / 2 Refer to Experiment 5 to see how to determine R based on V CC, V LED, and I. d) PostLab Question #4 / 2 VI) References / 1

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