Foundations of Technology

NPNNPN

© 2013 International Technology and Engineering Educators Association, STEMCenter for Teaching and Learning™ Foundations of Technology

Teacher Resource Unit 4 Lesson 4

Objective:You will build a simple circuit to show that a Negative-

Positive-Negative (NPN) transistor will serve as a current amplifier.

NPN

2N3904

Collector

Base

Emitter

The flat side faces up

You will need the following parts from your kit:1. Breadboard

2. 220 ohms resistor (red, red, brown, gold)

3. 3300 ohms resistor (orange, orange, red, gold)

4. NPN Transistor

5. 2 @ LED (light emitting diode)

6. 9 volt battery lead

7. 3 wires

8. 9 volt battery

9. Pushbutton switch

Use this schematic to construct the experiment.

220 Ohm

+

-9 volts

Quick Check:

Your circuit should like this one.

3.3K Ohmem

itter

colle

ctor

ba

se

This circuit will light the LED’s.

1. Electrons will not flow through the emitter collector until there is current through the emitter base combination.

2. This makes a small current control a large current which is referred to as amplification.

3. An increase of current through the emitter base will result in a larger current through the emitter collector side of the circuit.

4. 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. Connect the 9 volt battery.

2. Observe the brightness of the LED’s.

3. Press the pushbutton switch.

4. Observe and compare the brightness of the LED’s.

5. 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.