EMT 1255 Experiment #10 JFET Characteristics PDF

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Summary

Lecture - Prof. Jang (chairman and he is a terrible instructor)
Lab - Prof. Bustamante (Recommended) ...

Description

Experiment #: JFET Characteristics

Due Date: 05/11/2018 Objective

The objective of this experiment is to be able to measure and graph the drain characteristics curves for a junction field-effect transistor (JFET), measure the V GF (off) and I DSS for a JFET. Also we will be able to connect a JFET as two-terminal constant-current source to maintain constant illumination in an LED.

Equipment ● ● ● ●

One 100 ohms resistor One 10K ohms resistor One 2N5458 n channel JFET One milliammeter 0- 10 range

Procedure 1. We measured and recorded the values of the resistors listed in table 11-1. 2. We constructed the circuit shown in figure 11-2. 3. We started up by setting V GG and V DD at 0 V, then connected a voltmeter between the drain and source. We kept V GG a 0 and slowly increased V DD until the voltage across the drain and source was 1.0 V 4. With V DS at 1.0 V we measured the voltage across R2 (VR2). And then computed the drain current, I D, by applying ohm’s law to R2. 5. Without disturbing V GG, We slowly increased V DD to set V DS to 2.0 V then measured and recorded VR2 for this setting, once again we computed the current by applying ohm’s law the same way we did in step 4. 6. We repeated step 4 and 5 for each value of V DS listed in the table 11-2. 7. Once we were done recording the values listed on the table 11-2 for V DS, we adjusted VGG to -0.5 which previously was set to 0 V, once we had V GG set to -0.5, we proceed to repeat the steps 4-5. 8. We repeated step 7 twice more to get the values of the table when V GG was set to -1.0 V and -1.5 V.

Data

Questions • a) I DSS is found in a graph when the voltage across the drain and source is increasing but the current remain constant. The point where the current start to be constant between the increasing voltages is I DSS. • a) No. b) We can see from the graph that JFET is nonlinear because the current does not remain constant at all voltages, and does not vary on a constant rate. • The pitch off voltage for my JFET is 4.0 V across the drain and source. • We should only operate a JFET reverse bias on the gate source because, the drainsource current is largest when the gate-source voltage VGS is zero, typically about 50mA. Forward gate currents larger than 50mA will burn out the JFETs.

Conclusion

we were able to measure and graph the drain characteristics curves for a junction fieldeffect transistor (JFET), measure the V GF (off) and I DSS for a JFET. Unfortunately we were not able to complete the last to part of the experiment since we didn’t have enough time due to difficulties we faced when completing the table, we had to rebuild our circuit many times, and measure it many more times, we try out two different transistors and we still got the same results which didn’t match with the values we were expecting. With the help of our instructor we rebuilt our circuit one last time and we try one more different transistor which ended up being the problem. The first two transistors we tried were factory faulty, but once we replace it with the third transistor we got the values expected....