FUNDAMENTALS FOR THE BEGINNER
HOW AN NPN TRANSISTOR WORKS
A kit for these experiments can be purchased
from the Nuts & Volts Webstore at
www.nutsvolts.com or call us at 800-783-4624.
In this experiment, we will build a simple circuit to observe an
NPN transistor serving as a current amplifier.
1. Build the Circuit.
Using the schematic along with the pictorial diagram, place
the components on a solderless breadboard as shown. Verify
that your wiring is correct.
2. Do the Experiment.
Theory: In this circuit, the electrons flow from the negative
of the battery through the emitter, the base, LED1, the switch,
the 3,300 ohm resistor, then back to the positive of the battery.
At the same time, electrons flow through the collector, LED2,
and the 220 ohm resistor. Notice that electrons do not flow until
the switch is pressed. There must be emitter-base current before
any current will flow in the emitter-collector circuit. This act of a
smaller current controlling a larger current is referred to as
amplification. Within limits, as we increase the current in the
emitter-base circuit it will increase the current flowing in the
emitter-collector circuit. By adjusting the value of R1, you can
use an ammeter to observe the change in currents.
Procedure: Connect a nine-volt battery to the battery snap and
press the pushbutton switch to cause current to flow. Both LEDs
should light up. When you release the pushbutton switch, both
LEDs should turn off.
In doing this experiment, you can see that the NPN transistor is
working as a current amplifier, sending more current through
LED2 than LED1.
C = collector
E = emitter
These experiments are provided
by GSSTechEd at
You can order parts for this
experiment from their website
GK01049 220 ohm resistor
3.3K ohm resistor
Switch with wires