Lab 5: Transistor Switching

Introduction:
The purpose of this experiment is to demonstrate how a transistor works. Transistor is a semiconductor device which can switch the flow of the current. In this experiment, we are going to analyze the currents in the base and emitter portion of the 2N3904 transistor.

Procedure:
First we build the circuit same as diagram below:

with: R₁ =220 Ω, R₂ =10 KΩ, R₃ =680 Ω, Q₁ = 2N3904, D₁ =LED.

When we take out the resistor 2, and use our fingertip to connect the circuit, the LED still glows, even though our skin has a high resistance. There is only a trickle of voltage reaching the transistor, and the transistor still responds.

Now, take the LED out and build the circuit same as the diagram below:

Insert two multimeters A1 and A2 to measure the currents flow through the base and emitter portion.

Data:    A1 is the current flows through the base, and A2 is the current flow through the emitter.

A1 (mA)	A2 (mA)
0	0.1
0.1	34
0.134	36.2
0.2	42.5
0.31	47.3
0.44	51.6
0.58	53.5
0.75	54.7

The following graph represents our data points:

As we can see, the transistor becomes saturated when the emitter's current is about 40 mA.

The following graph will show where the most linear of the graph and the beta gain of the transistor is 64.42 which is the slope of the graph.