## EXPERIMENT 6 FET CHARACTERISTIC CURVES ________________________________________ Bring a diskette to save your data. ________________________________________ OBJECT: The objective of this lab is to investigate the DC characteristics and operation of a field effect transistor (FET). The FET recommended to be used in this lab is 2N5486 n-channel FET. • Gathering data for the DC characteristics ________________________________________ APPARATUS: Dual DC Power Supply, Voltmeter, and 1k resistors, 2N5486 N-Channel FET. ________________________________________ THEORY: A JFET (Junction Field Effect Transistor) is a three terminal device (drain, source, and gate) similar to the BJT. The difference between them is that the JFET is a voltage controlled constant current device, whereas BJT is a current controlled current source device. Whereas for BJT the relationship between an output parameter, iC, and an input parameter, iB, is given by a constant , the relationship in JFET between an output parameter, iD, and an input parameter, vGS, is more complex. PROCEDURE: Measuring ID versus VDS (Output Characteristics) 1. Build the circuit shown below. 2. Obtain the output characteristics i.e. ID versus VDS. a. Set VGS = 0. Vary the voltage across drain (VDS) from 0 to 8 V with steps of 1 V and measure the corresponding drain current (ID). b. Repeat the procedure for different values of VGS. (0V, -0.5V, -1V, -1.5V, -2V, -2.5V, -3.0V, -3.5V, -4.0V). 3. Record the values in Table 1 and plot the graph ID vs. VGS. VGS 0 -0.5 -1.0 -1.5` -2.0 -2.5 -3.0 -3.5 -4.0 VDS ID ID ID ID ID ID ID ID ID 0 0 0.002mA 0.002mA 0.002mA 0.002mA 0.002mA 0.002mA 0.002mA 0mA 1 0 0.7 mA 0.7 mA 0.66 mA 0.6 mA 0.6 mA 0.5 0.1mA 0mA 2 0 1.5 mA 1.3 mA 1.3mA 1.2 mA 1.1 mA 0.7 0.1mA 0mA 3 0 2.1 mA 2.6 mA 1.9 mA 1.8 mA 1.5 mA 0.8 mA 0.1mA 0mA 4 0 2.7 mA 2.6 mA 2.5 mA 2.4 mA 1.7 mA 0.8 mA 0.1mA 0mA 5 0 3.4 mA 3.3 mA 3.1 mA 2.8 mA 1.8 mA 0.9 mA 0.1mA 0mA 6 0 4.1 mA 3.4 mA 3.7 mA 3.2 mA 1.9 mA 0.9 mA 0.1mA 0mA 7 0 4.7 mA 4.5 mA 4.2 mA 3.4 mA 1.9 mA 0.9 mA 0.1mA 0mA 8 0 5.3 mA 5.1 mA 6.6 mA 3.5 mA 2.0 mA 0.9 mA 0.1mA 0mA Table 1. vds=0:8; id=[0 6.2e-3 9.7e-3 11.3e-3 11.9e-3 12.2e-3 12.3e-3 12.3e-3 12.32e-3]; plot(vds,id);grid on;hold on id2=[0 5.23e-3 8.05e-3 9.15e-3 9.57e-3 9.77e-3 9.88e-3 9.9e-3 9.92e-3]; plot(vds,id2);grid on;hold on id3=[0 4.29e-3 6.41e-3 7.17e-3 7.46e-3 7.60e-3 7.67e-3 7.73e-3 7.76e-3]; plot(vds,id3);grid on;hold on ________________________________________ Measuring ID versus VGS (Transconductance Characteristics) 1. For the same circuit, obtain the transconductance characteristics. i.e. ID versus VGS. a. Set a particular value of voltage for VDS, i.e. 5V. Start with a gate voltage VGS of 0 V, and measure the corresponding drain current (ID). b. Then decrease VGS in steps of 0.5 V until VGS is -4V. c. At each step record the drain current. VDS = 5 V VGS ID 0 3.42 mA -0.5 3.36 mA -1.00 3.27 mA -1.50 3.12 mA -2.00 2.79 mA -2.50 1.84 mA -3.00 0.71 mA -3.50 0.11 mA -4.00 0 mA Table 2. 2. Plot the graph with ID versus VGS using Excel, MATLAB, or some other program. Discussion Questions—Make sure you answer the following questions in your discussion. Use all of the data obtained to answer the following questions: 1. Discuss the output and transconductance curves obtained in lab? Are they what you expected? 2. Are the output characteristics spaced evenly? Should they be? 3. What are the applications of a JFET?

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