Using your measurements for Figs. 1, 2, and 3, plot the output voltages in the data I attached

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unabarrr

Engineering

Electrical Laboratory 1

The Catholic university of America

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There are two document one has the data which I did in class and the another one his the assignment I want you to answer the assignment using the data on the document I attached

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EXPERIMENT 3 SILICON DIODES OBJECTIVE To study the characteristics and applications of silicon diodes. THEORY Diodes are nonsymmetrical electrical devices. They conduct better when one end, called the anode, is positive with respect to the other end, called the cathode. Physical diodes are often marked with a line, like a minus sign, at the cathode, signifying that the diode will conduct better when this end is more negative than the other end. The symbol for a diode contains an arrowhead pointing from the anode to the cathode, which is the direction in which the current preferentially flows. There are several useful approximations to describe the operation of diodes in circuits: 1) Crude. The diode is a short circuit, like a closed switch, when voltage is applied in the forward direction, and an open circuit, like an open switch, when the voltage is applied in the reverse direction. This is also called the "ideal diode" approximation, and is usually a good starting point in understanding a new circuit. 2) Standard. The diode is a 0.7 volt source, with no series resistance, when voltage is applied in the forward direction, and an open circuit when the voltage is applied in the reverse direction. This somewhat better approximation tries to account for the voltage drop across the diode when current is flowing through it in the forward direction by saying that the voltage across the diode is always exactly 0.7 volts. 3) Theoretical. Theoretically, the current through many silicon diodes at room temperature is related to the voltage across them by the equation - 10 - V  kTV  26 mV I = I0  e − 1 ≈ I0 e   (3 − 1) where k is Boltzman’s constant, T is the absolute temperature, and Io is the “leakage” current when the diode is reverse biased. This approximation implies a theoretical value for the differential resistance of the forward conducting diode. The differential resistance of the diode, r, which is also called the "ac" resistance, relates the change in voltage to a change in current: rd = δV δI (3 − 2 ) where δV and δI are small changes in the voltage and current in the diode from its operating point. For many silicon diodes at room temperature r is given approximately by r= 26 mV ohms I (3 − 3) where I is the current in amps flowing through the diode. This resistance is often only a few ohms. It is in series with the 0.7 volts already present in the standard approximation. The current - voltage characteristics of the three models are shown with the figures. PROCEDURE - 11 - 1) Connect the circuit in Fig. 1, and apply voltages varying from -10 to 10 volts to the input, in one volt increments. With the digital voltmeter, measure and record the output voltages. How do your results compare with the crude approximation? How do they compare with the standard approximation? 2) Connect the circuit in Fig. 2, and apply voltages from -10 to 10 volts to the input, in one volt increments. With the digital voltmeter, measure and record the output voltages. Since the output does not change much, be sure to measure to three significant figures. How do your results compare with the crude approximation? How do they compare with the standard approximation? 3) Connect the circuit in Fig. 3 and apply voltages from -2 to 2 volts to the input, in 0.2 volt increments. With the digital voltmeter, measure and record the output voltages, again to 3 significant figures. This circuit is called a "limiter." It permits small input voltages to pass without attenuating them at all, but it limits the output to at most about ± 0.7 volt with large input voltages. Note that in the crude approximation this circuit would not work at all; the two ideal diodes "back to back" would simply constitute a short to ground and the output would always be zero. ASSIGNMENT Using your measurements for Figs. 1, 2, and 3, plot the output voltages, (Y axes), as a function of the input voltages, (X axes). On the same plots, show the outputs that would be expected in the crude and standard approximations. Use the data from the part 2 to compute the current flowing through the diode. This is the same as the current flowing through the 1 kΩ resistor, since there is no place else for that current to flow. The current through the 1 kΩ resistor may be computed, using Ohm's law, from - 12 - I= (Vin − Vout ) 1 kΩ (3 − 4 ) Plot the current flowing through the diode (Y axis) as a function of the output voltage, which is the voltage across the diode (X axis). On the same plot show the current - voltage relationship expected in the standard approximation. What is the maximum voltage difference between your experimental data and the standard approximation? Using the same data, compute the differential resistance of the diode from equation (3-2) by taking differences between successive data points for ∆V and ∆I. Plot the differential resistance (Y axis) as a function of the current (X axis) through the diode. The current used in this plot should be the average of the two successive values that form ∆I. For comparison, also plot equation (3-3) on the same graph. How does your plot of differential resistance compare with the theoretical approximation in equation (3-3)? - 13 - - 14 - - Vez -V Figures ou -lovo 6.26 -910 @ 733 z 631 65.29 -V 5114.3 -50 TV3-36 - 3U 2.36 2V90 0.63 I vo 21 O COMO Standard Crude Theoretical in o otvo? Out ZIK 1ka Curent Figure 1 0 0.7 Voltage Il veo 넝 Diode Models - Vorzo fo 호에 Fisurezi in you -9.96 1ks ar -9.04 V loul-20 9 0.67 Dr 0.68 7068 6v 6.67 5V 0.66 4r BV 0.63 2v 0.57 to out br -8.07 -> -7.05 - 60 -6.00 -5v 4.95 - 40 -4.00 -3V-3.09 -zu - 1.93 In O- 2.0 0.60 1kg 18 2.59 Ho Out 7.6 0.59 1.4 0.59 0.57 -1.2-0.52 -.Y-0.53 -1.6 - 0.55 -1.8 -0.55 Figure 3 - 2.0 -0.50 6.5Y Figure 2 0.60 14 -ir - 124
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I was having a hard time with this subject, and this was a great help.

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