TRANSISTORS AS SWITCHES

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TRANSISTORS AS SWITCHES
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TRANSISTORS AS SWITCHES
Common Formats
Advantages
Cost
Durability
Size
Efficiency
Silicone Chips now contain over a million
transistors for only a few pence each.
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How Transistors Work..
The transistor is a bipolar device made up from 3
layers of semi conductor materials
P type (good Conductor)
N type (poor Conductor)
P type
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How Transistors Work..
The transistor layers are termed
P
Collector
N
Base
P
Emitter
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How Transistors Work..
C
Apply Signal 0.6 Volts
P
N
Resistance of N type Semi-conductor Decreases
B
P
E
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How Transistors Work..
C
Apply Signal 0.6 Volts
P
The Transistor becomes an excellent
conductor Across the collector and emitter
N
B
P
E
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How Transistors Work..
The BC 108 is common general-purpose transistor.
The diagram below shows the position of the legs
when viewed from underneath the case.
The transistor has to be connected into circuits
correctly. The arrowhead on the emitter indicates
the direction of conventional current flow ?
that is, opposite to the electron flow.
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How Transistors Work..
Or apply Voltage Directly
c
If you apply Voltage Directly
b
e
0v
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How Transistors Work..
c
b
e
The Transistor must be protected from short
circuit by placing loads at the base and the
collector
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How Transistors Work..
c
c
b
b
e
e
Build the following circuit using crocodile clips
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How Transistors Circuits are built.
Transistor Circuit Group
Using input transducer devices that convert a
change in physical conditions into a change in
resistance and voltage. This can then be
processed in an electrical network based on a
voltage divider circuit.
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How Transistors Circuits are built.
Voltage Divider Circuit Group
Example 1 a simple voltage divider can be used
to fine tune the signal to the transistor
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How Transistors Circuits are built.
Thermistor Divider Circuit Group
Example 2 a thermistor in the voltage divider
can be used to trigger the transistor at a given
temperature
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How Transistors Circuits are built.
LDR Divider Circuit Group
Example 3 a LDR in the voltage divider can be
used to trigger the transistor at a given light
Level
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Build a circuit on a bread board
Problem Mr Mrs Beverage go regularly to their
local clubby. When coming home, usually too worse
for drink. They stot and fumble in the dark
trying to open the door for ages, causing him to
swear loudly and wake up Mr Walker next door.
Brief Design Mr Beverage a system that will
bring on a Light when it gets dark and has an
adjustment that can alter for summer time-
leaving Mr Beverage more money for drink.
Investigate LDR voltage divider configuration to
provide a darkness sensor
Design Build A proto type using a breadboard