BJT Lab

Problem 1

Design an experiment to calculate Beta for the following BJTs:  2N2222A, 2N3904, and 2N3906.  Make note of the base current used in the experiments and compare the values obtained to those found in the prep.  Measure Beta for two more 2N2222A BJTs and compare the three results.

P2N2222A

 Problem-1 (= =54.15) (= =21.1)

2N3904

 Problem-1 (= =12.4119) )= =21.1)

2N3906

 Problem-1 (= =8.235) (= =10.59)

Problem 2

Design an emitter follower amplifier (This will be referred to as a Class A amplifier in the Output Stage notes) and use two 2N2222A BJTs together to make a Darlington configuration.  Make DC measurements, plot the input and output sinewave, and explain what the circuit is doing verbally and with calculations.

Emitter Follower

 Problem-2 Input Voltage:   (50mV_{pk}) Input Current:   (309A) Output Current:   (3.4mA) Current Gain:   (=11)

emitter Follower

Darlington Pair

 Problem-3 Input Voltage:   (50mV_{pk})  Input Current:   (.04A) Output Current:   (.3A) Current Gain:   (=7.5)

Emitter follower 2

Problem 3

Design a Bypassed Common-Emitter amplifier with dual supplies using a fixed IB type of a biasing scheme to get a gain of -8V/V (± 0.5 V/V).   The input should be a 1 volt peak to peak sinewave with a frequency of 5 kHz.  Plot the output and input on the scope.  Also, plot vbe on the scope and comment on whether or not your circuit violates the small signal condition. (The peak value of vbe should be < 10 mV).  It will be difficult to get a clean signal on the scope for vbe so do your best.  We will not be strict on grading.)
 Problem-3 Yellow: InputLight Blue: OutputPink: Base VoltageDark Blue: Emitter VoltagePurple: Base-Emitter Voltage

bypassed

Problem 4

Purposefully violate the small signal condition by modifying the circuit or the input voltage used in part 3 and print the output that results.   Please do not make the signal so large you get clipping.  We are looking for non-linear gain distortion.

Problem-4

Problem 5

Make appropriate DC measurements in your circuit built in part 3) to determine your maximum signal swing.  Based on your measurements answer the following two questions: If the input voltage amplitude is increased will your circuit go into active mode or cut-off mode first?  What is the maximum peak to peak output you could expect before your circuit goes into active or cut-off mode?

Problem-5

Problem 6

Design a Bypassed Common-Emitter amplifier with dual supplies using the current mirror biasing scheme to get as large of a gain as possible.  Bonus points for highest gain.

problem-6

Problem 7

Build a Class B amplifier and print the output on the scope so that the cross over distortion can be easily seen (“zoom” into it).  Also, show how the output voltage changes when you connect the output to different load resistors (We have some power resistors in the lab you ).

Problem-7

Problem-7-Distortion

Rename 7 Changed Rl

Problem 8

Design a Class AB amplifier and print the output on the scope and show that the cross-over distortion has been removed.  Also, show how the output voltage changes when you adjust the value of your current source (made from a current mirror).  There are many different ways to bias a Class AB amplifier.  You are free to pick the one you want to try.

Problem-8

Measurements:

(Current Mirror: 2.00 mA)

(Current In: .02 mA)

(Current Out: 5.9 mA)

(Current Gain: ==295)

(Current Mirror: 5.5 mA)

(Output Voltage: 2.5mV_{pk})

Problem-8-scope

(Current Mirror: 1.99 mA)

(Output Voltage: 40mV_{pk})

Problem-8-Adjusted-Current-Mirror

Special Design

Using the provided photo-interrupter, build a circuit that turns on an LED and sounds an alarm when your ID is present in the channel.  To create the alarm, send a 500 Hz sine or square wave through a Class A, B, or AB amplifier with the speaker connected to the output.  You will have to build a circuit to generate the sine or square wave.  The trick will be to figure out how to have the speaker only make a sound when your ID is in the photo-interrupter channel. ONE MORE Requirement on this one:  Add in a relay to turn on the LED.  Even though the relay is not required for this circuit if you wanted to replace the LED with a high power lamp in the future it would be needed so it is good to get practice with them.