PC/CP320 Physical Computing
BJTs

Equipment

• BJT -- 2N3904 (Fairchild Semiconductor)

Procedure

1. Using a high current resistor of between 50 and 150 Ω for your load, wire up the circuit on the left of the drawing above with the BJT as your control element. Use a 12V supply and a 1 kΩ base resistor. Remember that when using a BJT, you always need a base resistor!

2. Using the variable voltage supply for the input to the base resistor, see what input voltages are required to produce a voltage across the load of 1V, 2V, 3V, 4V, and 5V.

3. Plot a graph of Vload vs. Vinput.

4. Replace the 1 kΩ base resistor with a 10 kΩ base resistor and repeat. What happens?

5. Now switch the positions of the load and the BJT, as in the right hand picture above. Use a 1 kΩ base resistor as in the original setup.

6. Repeat the investigation of input voltage required to produce each of the desired load voltages.

7. Plot the results on the same graph, and summarize how the relative positions of the load and control element affect the input voltage required.

Demonstrate the relationships between Vload and Vinput for the two configurations.

Resources

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