### 6.2.6 Transistors

```Transistors
Transistors
•
•
•
•
•
•
Transistors
Parts of the Transistor
The First Transistor
Transistors as Amplifiers
Transistors as Switches
Night Light Circuit
This presentation is intended to be used with Activity 6.2.6 Transistors
Transistors
Transistor: A small electronic device used in
a circuit as an amplifier or switch.
Symbol for Circuit
Diagrams
npn transistor
The First Transistor
•Considered by some to be the
greatest invention of the 20th
century
•Invented at Bell Laboratories
in 1947
•It is a crucial component in
almost all modern electronic
devices
•Engineers are working toward
making them smaller so that
more can be placed on
computer chips. Many today
human hair.
Replica
Parts of the Transistor
EMITTER
BASE
COLLECTOR
The small base current controls the larger collector
current.
How It Works
When there is no current
to the base, no current
can flow between the
collector and the emitter,
and the transistor is off.
A small current to the base enables
the transistor to conduct current from
the collector to the emitter, and
allows a larger current to flow
through the transistor. Components
connected to the collector can use
this larger current.
How it Works
EMITTER
BASE
COLLECTOR
The small base current controls the larger collector current.
Transistors as Amplifiers
(input)
(output)
Transistors as Switches
Draw the schematic
diagram for the circuit as
shown using 6 DC volts.
When the push switch is closed,
you should notice that the LED in
the circuit connected to the base is
very dim.
But the other LED that is controlled
is much brighter.
DC
1K
A small current amount switching
on a larger current
Small Current
5.1 K
Large
Current
Night Light Circuit
Challenge: Create a system with a light that comes on
when it is dark, similar to a street light.
In the following circuit, will the LED be bright (on) at day or night?
The LED will be bright during the day
because brightness causes the
photoresistor’s resistance to
decrease.
When the resistance of the circuit
decreases, more current can flow to
the LED.
Night Light Circuit
1 KΩ
10 KΩ
Current will always take the path of
least resistance.
Does current reach the base of the
transistor?
Will current be able to reach the
light?
Night Light Circuit
1 KΩ
10 KΩ
In brightness the photoresistor’s
resistance is low.
Does voltage reach the base of the
transistor?
Will voltage be able to reach the
light?
Night Light Circuit
1 KΩ
10 KΩ
In darkness the photoresistor’s
resistance is high.
Will the base circuit of the transistor
be activated?
Will current be able to reach the
light?
Night Light Circuit
Build the circuit as shown using 6 DC volts to test using actual components using
Snap Circuits® spring sockets.
1 KΩ
10 KΩ
On Pg. 7 use the following to fill in
the blanks:
• Low or high
• Insulator or conductor
• Closed (on) or Open (off)
If the circuit does not work as expected, troubleshoot using the
flow chart provided in Activity 6.2.6 Transistors (omit the
suggestion to check solder connections).
Night Light Circuit
Create a permanent night light circuit.
Once you have tested all components to ensure that they are working
properly, solder them to a permanent board as shown by your instructor.