MORGAN STATE UNIVERSITY DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING EEGR.215 Materials and Devices Spring 2017 Credits – 4 Written LAB DUE DATE: April 21, 2017 Lab #5: The Zener Diode and Diode Applications Objective: This is the second lab of a group of labs on basic semiconductor components. The student will study semiconductor characteristics (I-V, rectification) and some of their applications. This particular lab will study the zener diode and the diode rectification properties. The student will measure the zener diode’s I-V characteristics and half-wave and full-wave rectification performance. The student will graph these characteristics in EXCEL. Background: The zener diode has properties similar to those of the pn junction diode investigated in the previous lab. The circuit symbol is shown in Figure 1 below. + - Figure 1. Circuit symbol of a zener diode. In the forward-biased direction, the current through a zener diode is given by Vz Izener(V) Isat(eqnVT 1) for Vz > 0 Unlike the pn junction diode investigated in the previous lab, the zener diode can have current flow in the reverse-biased direction. This current flow occurs at a specific zener reverse voltage. Current flow in the reverse direction does not occur until this zener voltage is reached. If the reverse voltage is greater than the zener voltage then current flow will not be maintained. Therefore, zener diodes are often used as voltage regulators in analog circuits. Voltage regulators hold the output voltage at a fixed value; this is very useful for power supply circuits. A class of circuits known as rectifiers use one or more diodes to change an AC input voltage into a constant DC voltage that is either positive or negative. Rectifiers can be made with pn junction diodes because diodes favor current flow in one direction only. The simpliest type of rectifier is the halfwave rectifier, it incorporates one diode in the circuit topology. The half-wave rectifier eliminates the unwanted polarity of the input waveform. Unlike the half-wave recitifier, the bridge rectifier incorporates four diodes in the circuit topology and is able to take both the positive and negative parts of an AC signal and provide full-wave rectification. Equipment Needed: Power Supply (3)Resistor (1 kΩ) (5) Silicon Diode (1N4148) (1) Zener Diode (1N4737A) Voltmeter Ammeter ADS PART 1. Zener Diode Characteristics Build the circuit with a Zener diode as shown in Figure 2. R k + + VZ VS= 5V _ Figure 2 1.1 Measure the diode voltage Vz (obtain a zener diode from lab) as the power supply is varied from 0 to 10 volts using the steps given in Table 1. Record Vz, VR and Iz. Table 1 Measurement results for simple zener diode circuit Source Volage, Vs (Volts) 0 0.2 0.4 0.6 0.8 1.0 2 3 4 5 6 7 8 9 10 Diode Voltage Vz (Volts) 0.51 mV 225.60 mV 0.4082 V 0.5942 V 0.6785 V 0.7004 V 0.7396 V 0.7543 V 0.7637 V 0.7705 V 0.7754 V 0.7801 V 0.7832 V 0.7856 V 0.7884 V Resistor Voltage VR (Volts) 0 mV 0 mV 0 mV 9.84 mV 137.54 mV 299.97 mV 1.3042 V 2.2875 V 3.293 V 4.296 V 5.261 V 6.337 V 7.296 V 8.317 V 9.333 V Calculated Iz=VR/R (mA) 0 mA 0 mA 0 mA 0.00984 mA 0.1375 mA 0.3 mA 1.3042 mA 2.3 mA 3.3 mA 4.2 mA 5.3 mA 6.337 mA 7.3 mA 8.32 mA 9.3 mA 1.2 Continue measuring the circuit, this time apply the negative voltages given in Table 2 and record the results. Table 2 Measurement results for simple zener diode circuit Source Volage, Vs (Volts) 0 -0.2 -0.4 -0.6 -0.8 Diode Voltage VZ (Volts) 0.43 mV 198.30 mV 0.4035 V 0.5964 V 0.6754 V Resistor Voltage VR (Volts) 0V 0V 0.02 mV 8.60 mV 127.12 mV Calculated Iz=VR/R 0 mA 0 mA 0.00002 mA 0.0086 mA 0.12712 mA -1.0 -2 -3 -4 -5 -6 -7 -8 -9 -10 1.3 What is the zener voltage for this particular Zener diode? _______________ 1.4 Using the data in Tables 1 and 2, using EXCEL graph the forward and reverse I-V characteristics for the Zener diode. PART 2. Half-Wave Rectifier Build the rectifier circuit shown in Figure 3 below using silicon pn junction diodes (Use 1N4148). Figure 3. Single diode rectifier 2.1 Using the function generator set up the signal source (Vs). Use a sine wave at 500 Hz with a peak amplitude of 8 Volts. ( Vs = 8 sin(2 500t) ) 2.2 Use the oscilloscope to display both the input and the output at the same time. Sketch these waveforms (Make sure to note the y-axis and x-axis scale and units). Use graph paper to sketch your waveforms. 2.3 Using a DC voltmeter, record the input and output voltages. 2.4 Set your oscilloscope to X-Y setting. This will display channel-1 (your input) on the X axis and channel -2 (the output of the circuit) on the Y axis. This will display the transfer characteristic of your circuit. Sketch the transfer characteristic you observe and comment. (Make sure to label the y-axis and xaxis.) PART 3. Full-Wave Rectifier The half-wave rectifier circuit is not very effective as a rectifier since it uses only one half period of the sine wave. A more commonly used circuit is the bridge rectifier. Build the bridge rectifier shown in Figure 4 using regular silicon pn junction diodes (1N4148). Figure 4. Bridge diode rectifier 3.1 Using the function generator set up the signal source (Vs). Use a sine wave at 500 Hz with a peak amplitude of 4 Volts. ( Vs = 4 sin(2 500t) ) 3.2 Use the oscilloscope to display both the input and the output at the same time (Make sure you are not in X-Y mode, but in normal time measurement). Sketch these waveforms (Make sure to note the y-axis and x-axis scale and units). To properly measure Vo, connect channel-1 of the oscilloscope to the positive end of the resistor (Va). Connect channel-2 of the oscilloscope to the negative end of the resistor (Vb) while connecting the common ends of both channels to Vref. Display both channels and select “add” mode on the oscilloscope. This will give you Va + Vb. Use the “Invert Channel-2” option to get Va + Vb which is equivalent to Vo. 3.3 Is a true DC signal seen at Vo? If not, then what additional components can be used to obtain a true DC signal? Extra Credit (50 points): Simulate the half-wave and bridge rectifiers in parts 2 and 3 in ADS. Compare simulation with measured results. Comment on any similarities or differences between the results. Make sure to show the schematics and plots of the input and output waveforms for each circuit. (Hint: Use the Vt sine source from Transient sources palette if using ADS.)
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