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EE2201 E2002 LAB 1 - Diode Characteristics PRELAB P1. For the diode circuit of Fig. P1-1, choose a value of R1 that will give a diode current of iD ≈ 10µA. (Assume iL = 0) P2. Choose a value of R1 that will give a diode current of iD ≈ 10mA. iR R1 iD D1 iL + +10V + VD - Fig. P1-1. P3. For the diode rectifier circuits of Fig. P1-2(a) and (b), plot (as a function of time) vOUT and iD when vIN is a 1kHz sine wave with peak amplitude of 5V. P4. For the diode rectifier circuits of Fig. P1-2(a) and (b), plot the input-output transfer characteristic (vOUT as a function of vIN). R2 10kž D3 + vIN + + iD - D2 vIN VOUT - - Fig. P1-2(a) iD R3 10kž Fig. P1-2(b) 1 + VOUT - EE2201 E2002 LAB 1 - Diode Characteristics PURPOSE: The purpose of this laboratory assignment is to investigate the operation of two types of p-n junction diodes, the 1N4148 and 1N4004. Upon completion of this lab you should be able to: Measure and plot the V-I terminal characteristics of a diode. Determine the exponential model parameters IS and n. Build rectifying circuits that take advantage of the nonlinear V-I characteristic of the diode. Use the oscilloscope X-Y mode to display the transfer characteristics of diode circuits. MATERIALS: ECE Lab Kit DC Power Supply DVM Function Generator Oscilloscope NOTE: Be sure to record ALL results in your laboratory notebook. Diode pin designation reminder: Band on package indicates cathode: ANODE CATHODE BAND 2 1N4148 DIODE: V-I CHARACTERISTIC V-I Characteristic: Forward bias L1. Build the diode circuit shown in Fig. 1-1, using the 1N4148 for diode D1. By using different values for resistor R1, you will measure the diode voltage vD as diode current iD varies over a three decade range from approximately 10µA to 10mA. iR R1 iL + +10V iD D1 + VD - Figure 1-1. L2. Vary R1 to cover the range 1kΩ to 1MΩ in logarithmic fashion using the values: 1kΩ, 2kΩ, 5.1kΩ, 10kΩ, 20kΩ, 51kΩ,100kΩ, 200kΩ, 510kΩ, 1MΩ. In each case, record the diode voltage vD and calculate the diode current iD from 10V v D iD (1) R1 Note that Eq. (1) assumes iL is negligible, so that iD≈iR. L3. Measurement note: to ensure accuracy in determining iD: Using the DVM, measure the actual values of the resistors used for R1. Since the resistor value has a tolerance of ±5%, using the nominal value of R1 in Eq. (1) would give an uncertainty of ±5% in the calculated value of iD. To set the supply voltage to 10V, measure the output using the DVM. The meter on the power supply isn’t very accurate (a few percent at best); using the DVM allows you to realize an accuracy of better than ±0.1% in the 10V term in Eq. (1). When measuring vD, use the DVM on the 2V scale to get mV resolution. You’re looking for small changes in vD, so it's important to measure with as fine a resolution as possible. Constant-voltage-drop model L4. If you were modeling this diode with a constant-voltage-drop model, what voltage would you use to model operation for currents near 5mA? 3 V-I Characteristic: Reverse bias L5. Reconfigure the power supply connections to apply a negative voltage to the diode, as shown in Fig. 1-2. Also reconfigure the DVM to measure the voltage drop across the 1MΩ resistor R1. iD D1 iL + VD + + VSUPPLY iR1 R1 1Mž + VR1 - DVM - Figure 1-2. L6. Sweep the power supply from 0V to 10V (use increments of 1 or 2V), and record the voltage drop across R1. Calculate the voltage on the reverse biased diode from vD = vR1 – vSUPPLY (2) Also calculate the current that flows in each case, from v (3) iD R1 R1 Note that Eq. (3) assumes iL is negligible, so that iD≈-iR. 1N4004 DIODE: V-I CHARACTERISTIC L7. Repeat parts L1 though L6, using the 1N4004 diode for D1. 4 CLIPPING CIRCUIT L8. The intended function of this circuit is to (ideally) pass the input signal unchanged to the output when vIN is positive, and “clip” the negative portion of the signal so that vOUT=0 when vIN is negative. R2 10kž + + vIN D2 - VOUT - Figure 1-3. Input, output waveforms L9. Build the diode circuit shown in Fig. 1-3, using the 1N4148 for diode D2. Use the function generator to set up the input signal source vIN=(5V)sin(2[1kHz]t), a 5V peak sine wave at a frequency of 1kHz. L10. Set up the oscilloscope to view vIN on channel 1 at 2V/div, and vOUT on channel 2 at 2V/div. Set both inputs to zero (GND) and adjust the vertical position of each trace so that both are centered vertically. Once the vertical position is adjusted correctly, when viewing the voltage waveforms, be sure both channels are on DC coupling. Set up the time base of the scope to show at least one full cycle of the sine wave. L11. Sketch the input and output waveforms as shown on the oscilloscope. How well does this circuit meet the functional goal expressed in section L8? Transfer characteristic L12. Change the display format of the oscilloscope to XY. This will display channel 1 (vIN) on the horizontal axis, and channel 2 (vOUT) on the vertical axis. The result will be a plot of vOUT as a function of vIN: the transfer characteristic. L13. Sketch the transfer characteristic. How does it compare with the functional goal expressed in section L8? Limit of clipping behavior L14. Change the display format of the oscilloscope back to the YT format of section L10. Reduce the input amplitude until clipping behavior is no longer evident in the output waveform. At what amplitude does the circuit stop performing the clipping function? 5 RECTIFYING CIRCUIT L15. The intended function of this circuit is to (ideally) allow vIN to provide current through D3 to R3 (with vOUT=vIN) when vIN is positive, and allow no current through D3 to R3 (with vOUT=0) when vIN is negative. D3 + vIN - R3 10kž + VOUT - Figure 1-4. Input, output waveforms L16. Build the diode circuit shown in Fig. 1-4, using the 1N4004 for diode D3. Use the function generator to set up the input signal source vIN=(5V)sin(2[100Hz]t), a 5V peak sine wave at a frequency of 100Hz. L17. Set up the oscilloscope to view vIN on channel 1 at 2V/div, and vOUT on channel 2 at 2V/div. Set both inputs to zero (GND) and adjust the vertical position of each trace so that both are centered vertically. Once the vertical position is adjusted correctly, when viewing the voltage waveforms, be sure both channels are on DC coupling. Set up the time base of the scope to show at least one full cycle of the sine wave. L18. Sketch the input and output waveforms as shown on the oscilloscope. How well does this circuit meet the functional goal expressed in section L15? Transfer characteristic L19. Change the display format of the oscilloscope to XY. This will display channel 1 (vIN) on the horizontal axis, and channel 2 (vOUT) on the vertical axis. The result will be a plot of vOUT as a function of vIN: the transfer characteristic. L20. Sketch the transfer characteristic. How does it compare with the functional goal expressed in section L15? Limit of rectifying behavior L21. Change the display format of the oscilloscope back to the YT format of section L17. Reduce the input amplitude until rectifying behavior is no longer evident in the output waveform. At what amplitude does the circuit stop performing the rectifying function? 6 LAB WRITEUP 1N4148 AND 1N4004 DIODES: V-I CHARACTERISTIC For each of the 1N4148 and 1N4004: W1. Using your measured data, plot the overall V-I characteristic (both forward and reverse bias) on linear axes. Identify the forward and reverse bias regions. W2. On the same axes with your data plot from section W1, plot the V-I characteristic of the constant-voltage-drop model you determined in section L4. W3. Discussion: Compare your measured data to the constant-voltage-drop model. How well does the constant-voltage-drop model predict the diode’s V-I behavior? Are there any deviations from the model (e.g. at low currents or high currents)? W4. Plot the forward bias data on semilog axes (X axis: linear scale for vD; Y axis: logarithmic scale for iD). Alternatively, use linear axes to plot ln(iD) as a function of vD. In either case, the data points should fall on a straight line if the exponential model holds for the V-I characteristic. W5. Determine the exponential model parameters IS and n. W6. Discussion: Compare your measured data to the exponential model by plotting the exponential model equation on the same axes with your data plot from section W4. How well does the exponential model predict the diode’s V-I behavior? Are there any deviations from the model (e.g. at low currents or high currents)? W7. Discussion: Compare the constant-voltage-drop and the exponential models: Which is more accurate? Which is easier to use in circuit design and analysis? Note the tradeoff between model accuracy and ease of use – a recurring theme in modeling nonlinear devices. CLIPPING CIRCUIT W8. In the case of the 5V peak sine wave input, plot (as a function of time) the measured v IN and vOUT waveforms. Also, calculate and plot the diode voltage vD and diode current iD. On your plot, identify the diode operating regions (forward and reverse bias). W9. Plot the transfer characteristic from your X-Y plot in section L12. W10. Discussion: given your results in W8 and W9, how well does this circuit’s performance compare with the functional goal expressed in section L8? W11. What was the limiting amplitude below which the circuit could no longer perform the clipping function? 7 W12. Discussion: Explain what causes the limit observed in W11. 8 RECTIFYING CIRCUIT W13. In the case of the 5V peak sine wave input, plot (as a function of time) the measured v IN and vOUT waveforms. Also, calculate and plot the diode voltage vD and diode current iD. On your plot, identify the diode operating regions (forward and reverse bias). W14. What was the largest reverse bias voltage on the diode? (Note: this is also called the Peak Inverse Voltage, or PIV, and will be important in the design of rectifier circuit when we consider the problem of reverse breakdown). W15. Plot the transfer characteristic from your X-Y plot in section L19. W16. Discussion: given your results in W13 and W15, how well does this circuit’s performance compare with the functional goal expressed in section L15? W17. What was the limiting amplitude below which the circuit could no longer perform the rectifying function? W18. Discussion: Explain what causes the limit observed in W17. 9