UChicago Instructional Physics Laboratories

Resistors: 270ΩΩ { $\Omega$ , 470ΩΩ { $\Omega$ , 820ΩΩ { $\Omega$ , 1k, 3.3k, 33k Capacitors: 4.7μμ { $\mu$ F  2x multimeters

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For npn Bipolar-Junction Transistors(BJTS), there are three well-defined behavior regimes, as shown below.  Note that this is a first-order model; real devices will exhibit small deviations depending on their construction.

What this is asking you to do:

To use the diode test mode of your meter, turn the switch to the picture of a diode and push the yellow button until a diode is shown in the top right corner.

Connect the leads across the different metal legs of the transistor systematically; there should be one pin that connects to the other two via pn-junctions.

The direction of the junction (from anode to cathode) is from the COM lead to the red lead.

This is a tip, not an instruction.

The (B)ase, (C)ollector, and (E)mitter pins of your transistor are as shown below:

{ ${/download/attachments/205261936/2N3904.png?version=1&modificationDate=1555511845000&api=v2}$ 5 kHz is a reasonable starting place for your sine wave; anything above 20 kHz may start to distort

Footnote 2 basically notes that if VinVin { $V_{in}$  is around -6V or less, our transistor model breaks down and there can be current in the “wrong” direction (opposing the direction of the arrow)

The instructions in the book are fairly hard to follow, so an alternative version is laid out below:

Input/Output Impedance

Use the circuit below to test the transistor circuit's input impedance (i.e., how much it will affect another circuit's output when it is connected)

{ ${/download/attachments/205261936/Lab4_inputImpedance.png?version=1&modificationDate=1555440905000&api=v2}$ Setting both channel 1 and channel 2 of your scope to AC coupling here may make your life easier.

Using a VinVin { $V_{in}$ of ~ 1V in amplitude and several kHz in frequency, adjust RR { $R$ (by using larger resistors or connecting some resistors in series) until the amplitude of VoutVout { $V_{out}$ is about half the amplitude of VinVin { $V_{in}$ . At this point, R is equal to the circuit's input impedance. What is the ratio of { $R$ to [Math Processing Error] { $R_E$ when this happens? Use the circuit below to test the transistor circuit's output impedance (i.e., how sensitive the circuit is to having other elements connected to { $V_{out}$ ) { ${/download/attachments/205261936/Lab4_OutputImpedance.png?version=1&modificationDate=1555440919000&api=v2}$ Now, again using using a { $V_{in}$ of about 1 V in amplitude and several kHz in frequency, adjust [Math Processing Error] { $R_{load}$ until [Math Processing Error] { $V_{out}$ is half the amplitude of [Math Processing Error] { $V_{in}$ . At this point, [Math Processing Error] { $R_{load}$ is equal to the circuit's output impedance. What is the ratio of [Math Processing Error] { $R_{load}$ to [Math Processing Error] { $R_B$ ? (Please do not attach loads smaller than 50 ohms, they may get unreasonably hot)

4L.3 Current source

Remember that to measure current, you need to use the COM and mA/10A ports on your multimeter and place it in series with the component you'd like to measure.

Use the resistor substitution box as a 10k variable load.

When thinking about voltage compliance, at what collector voltage does the current begin to drop?  What else is this voltage related to?

4L.4 Skip this

4L.5 Transistor switch

The power transistor we use is configured differently than our previous transistor, as shown below.

{ ${/download/attachments/205261936/MJE3055.png?version=2&modificationDate=1555521460000&api=v2}$ Stop after switch portion, don't continue to 5.1 or 5.2