The preferred Exercise is shown in Exercises 5B or 5C.

Transcription

1 ECE 231 Laboratory Exercise 5A The preferred Exercise is shown in Exercises 5B or 5C. Laboratory Group (Names) OBJECTIVES Validate the Schottky diode equation. Calculate the dc and dynamic (ac) resistance of a diode. Observe the rectifying characteristics of a diode. EQUIPMENT REQUIRED ECE 231 Circuit Board (In Stock room) Two banana cables (one for DC power supply and one for DMM) One lot of clip leads and/or jumper wires DMM (digital multimeter) One DC power supply One diode Four or more resistors (available in bins adjacent to the 5 th floor stock BACKGROUND The Schottky diode equation (1) is a very good approximation of how an actual diode behaves in the laboratory. The plot of this equation is shown in Figure 1. The experiment will be to investigate the properties of a diode in quadrant I and III. Most diodes if operated in the breakdown region (far left) will be destroyed. There are however diodes made to operate in this region, and they are called zener diodes. The next region (center) is the reverse region. This is the normal region when a diode is reverse biased. The next region, quadrant I, is the normal forward biased region. I diode = I s (e V D/(nV T ) 1) Some definitions I s is the reverse saturation current and is approximately equal to 1-12 A. It is sometimes referred to as I o or I r. This current is proportional to the area of the diode. We will not measure this current in this experiment. V D = diode voltage, n is approximately 1 to 2. Use 1 for this lab. V T is 26 mv at 3 o K. 1

2 V D should be in the range of.6 to.75 V for silicon diodes and.3 V for germanium diodes.is usually taken as 1. Some industrial diodes can be several inches in diameter. Common ones used by students are shown in Figure 2. The ones used on circuit boards with surface mounted components are only about 1 or 2 mm across. See Figure 3 for typical electronic schematic symbols for diodes. Photodiodes may receive light or output light (Light Emitting Diode LED). Zener diodes are designed to operate in the breakdown region. There breakdown voltage can range from several volts to tens of volts. Figure 1. Plot of diode characteristic equation. Source: Wikimedia Commons 2

3 Figure 2. An assortment of typical diodes. Anode + - Anode Cathode + - Zener diode Cathode General purpose diode Photodiode or LED Figure 3. Electronic symbols for diodes. PROCEDURE Part 1 1. Construct the circuit shown in Figure 4 on the protoboard. Identify three resistors on the protoboards with values of 1, 1K, and 1K. Measure the resistor values using 3

4 the multimeter. Do not use the color code to determine the resistance value. You are going to construct three circuits using these resistors. 2. Measure and calculate the voltages, currents, and r ac for Table 1. r ac = V i = V V 8 V i 12 V i 8 V D1 V1 Vs 1Vdc V1 DIODE R1 Multimeter (volts) R1 = 1 R1 = 1 R1 = 1 Figure 4. Linear resistor network. Table 1. Diode Data Vs = 1 I diode= V diode= Plot data in Figure 5 V1/R1 Vs-V1 rac R1 I = V1/R1 Vdiode = Vs-V1 Vs = 8 R1 = 1 1 Vs = 12 R1 = 1 1 r ac = 1 3. Plot the diode curve in Figure 5. Alternatively, you can copy the oscilloscope display and paste it in your lab report when performing experiments 5B or 5C. 4. Connect the circuit shown in Figure 4, but replace the DC sources with a 1 KHz, 5 V sine wave and replace the multimeter with the oscilloscope. Set R1 = 1 ohms. Draw your results in Figure 6. 4

5 1 9 8 Current -ma Diode Voltage X 1-1 Figure 5. Diode Characteristic Curve Voltage

6 Time Figure 6. ½ Wave rectifier oscilloscope trace 1. Write a professional comprehensive lab report using a word processor. Show your results and include a comprehensive conclusion. There are lots of sample lab reports on the internet. Conclusion 6