Download ECEN 3711 -- BJTs, the Curve Tracer, and a DTL Circuit -

ECEN 3711
BJTs, the Curve Tracer, and a DTL Circuit [10 points]
Lab #7
Purpose: To use the Tektronix 577 curve tracer to obtain I-V traces for a BJT (Bipolar Junction
Transistor), to take measurements of a simple BJT DTL circuit, and to use PSpice for BJT circuit
simulation.
Equipment: CADET Trainer, variable DC supply, Tektronix 577 curve tracer, oscilloscope (with
10:1 probe), digital multimeter. You should have a spec sheet for the 2N2222 BJT.
Procedure: Listen and take notes as needed while your instructor introduces the BJT and demonstrates how to use the 577 curve tracer to display BJT characteristics. We will use 2N2222 npn bipolar
junction transistors and suitable diodes (1N4002) for this lab experiment.
In the work below, please do #1 and then relinquish the 577 to another group. You may watch another
group work with its BJT, but please get your own 577 data with your own BJT.
1. When a 577 is available, insert a 2N2222 into its test socket. Carefully adjust sweep (VCE) and the
display to show the normal forward-mode common-emitter characteristics for VCE from 0 to 10 V
(horizontal axis) and IC from 0 to 10 mA (vertical axis). Base-current steps and VCE series resistance should be set to fill about ¾ of the screen. Sketch or photograph the characteristics. Be sure
to label axes and family values. Also, carefully find the maximum (breakdown) VCE.
With the device still in the test fixture, find the base current, IB, needed to give (IC, VCE) = (2 mA,
2 V) and calculate F at this point. Next find the cutoff current (use VCE = 4 V), and then find the
saturation voltage (use IC = 4 mA). Compare these values with the spec sheet.
[1.5 pts]
2. Build this circuit on an SK board. Monitor Vo
with the oscilloscope (using a 10:1 probe) to be
sure the circuit does not oscillate* and be sure the
scope’s vertical input is set to be sensitive to small
signals. Use a DMM to obtain a table of Vo versus
Va and Vb with each of the four combinations of 0
and 3.5 V applied.
[1 pt]
3. Continue to monitor Vo and take adequately
detailed measurements of Vo and each VBE for
0 ≤ Va ≤ 3.5 V with Vb = 0 V. Repeat with
0 ≤ (Va=Vb) ≤ 3.5 V.
[1.5 pts]
4. Discuss and evaluate your results. What kind of logic gate is this circuit? Describe what the
oscilloscope showed, especially for the range when Vo was changing.
[1 pt]
5. Run an OrCAD/PSpice DC sweep of Vo vs. 0 ≤ (Va=Vb) ≤ 3.5 V. Find and use the Q2N2222 BJT
for your circuit. Compare with experimental results. Do another plot showing input current, Ia,
versus the same input voltages.
[3 pts]
As always, nice tables and plots are expected for this lab. [2 pts]
*Notes: Add a 0.1μF capacitor between the 3.5 and 0 V lines near their source, but on your SK board. This is called a decoupling
capacitor and will minimize transient signals in the power-supply lines.
Take care how you wire your experimental circuit. Be sure that only power (0 and 3.5 V feeds) are run in the long (vertical)
double SK socket runs. Those runs should not be used for signal connections.
Avoid using extra junction points. Wire neatly with reasonable length wires, and make convenient use of colors to help you
debug. Consider the need to be able to remove a chip/device for testing or substitution without messing up your wiring.
P.Munro 03-May-2017 05:17 AM