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Foundations of Technology
NPN
Teacher Resource Unit 4 Lesson 4
© 2013 International Technology and Engineering Educators Association,
STEMCenter for Teaching and Learning™
Foundations of Technology
Objective:
You will build a simple circuit to show that a NegativePositive-Negative (NPN) transistor will serve as a
current amplifier.
Collector
NPN
Base
2N3904
Emitter
The flat side faces up
You will need the following parts from your kit:
1.
2.
3.
4.
5.
6.
7.
8.
9.
Breadboard
220 ohms resistor (red, red, brown, gold)
3300 ohms resistor (orange, orange, red, gold)
NPN Transistor
2 @ LED (light emitting diode)
9 volt battery lead
3 wires
9 volt battery
Pushbutton switch
Use this schematic to construct the experiment.
base
220 Ohm
3.3K Ohm
+
9 volts
-
Quick Check:
Your circuit should like this one.
1.
2.
3.
4.
This circuit will light the LED’s.
Electrons will not flow through the emitter collector
until there is current through the emitter base
combination.
This makes a small current control a large current
which is referred to as amplification.
An increase of current through the emitter base will
result in a larger current through the emitter
collector side of the circuit.
If you change the 3.3K Ohm resistor you will see a
change in LED brightness. You can also measure
this with your Amp meter.
1.
2.
3.
4.
5.
Connect the 9 volt battery.
Observe the brightness of the LED’s.
Press the pushbutton switch.
Observe and compare the brightness of the LED’s.
Release the pushbutton, both LED’s should turn
off.
Troubleshooting:
1. If the LED’s do not light up, check to make sure they are in correctly.
2. Check the battery. Does it have voltage?
3. Are there any breaks in the circuit?
4. Is the NPN in the right way?
By completing this experiment, you should have
noticed the light from the LED on the emitter
collector was brighter than the LED from the emitter
base. The LED’s only light up after you press the
button.
In complete sentences, write what you learned about
a NPN transistor in a circuit.