Transcript Electronics - Mill Creek High School

Electronics
Chapter 12
Objectives
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Identify the value of resistors based on the
resistor color code
State the purpose of using capacitors in
conjunction with resistors for timing functions
Recognize purpose of common electronic
components (resistor, capacitor, diode)
Explain purpose of specific ICs
Convert schematics into electronic circuits
Construct and troubleshoot electronic circuits
Electronics: definitions
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Electronics: science that deals with electron flow
Becomes a technology when applied to serve a
useful purpose (camera, stereo, computer, etc)
Electronic Circuit: a group of electronic
components designed to perform a certain,
specific, function.
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standard components are used in different ways
Electronic Device: made of one or more
electronic circuits
Resistors
 Resistors:
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restrict the flow of electrons
To protect components from burning out
To modify recharging times for batteries
and capacitors
Ohm: unit of measurement for resistance
 Amount
of resistance in a resistor is
determined by reading the colored bands on
the resistor
Reading a resistor
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Four-band resistor
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Five band resistor:
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First TWO bands - represent digits
Third band - represents the multiplier
Fourth band – represents the resistance
tolerance
First THREE bands - represent digits
Fourth band - represents the multiplier
Fifth band – represents the resistance tolerance
Note: any resistor with no tolerance band has
a tolerance of +/- 20%
Resistor Color Band Chart
Troubleshooting Resistors
 Calculate
the value of the resistor using
the bands
 Measure resistance using a multi-meter
 If it is not within the tolerance the resistor
has failed
 (BE SURE THERE IS NO POWER FIRST!!!)
Variable Resistors
 Amount
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Dimmer switches on lights at home
Volume controls on stereos
 How
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or resistance is adjustable
they work
Inside is a length of resistance material (often
carbon)
The wiper slides along the resistance wire when
knob is turned
The greater distance
that the electrons flow
through the resistance
material the more
restricted the flow
Capacitors
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Ability to store (and discharge) electrical
charge very quickly
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Used to smooth out variations in power pulses
Ie: AC units, TV’s , camera flashes, etc
Farad (F): unit for measuring capacity
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Most capacitors are rated in microfarads
(millionths) or picofarads (trillionths)
Most capacitors rate only a few microfarads
Capacitor types
 Ceramic
Disk: made of ceramic and silver
 Electrolitic: made of an electrolyte and
aluminum
Diodes
 Allows
for only one way
flow of electricity
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(similar to a check valve
in a fluid system)
 Can
also serve as a
switch only allowing the
flow of electricity when it
reaches a certain
voltage.
 Size usually indicates the
amperage rating
Diodes
 Electricity
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can only flow:
INTO the diode through the cathode
OUT OF the diode through the Anode
 This
is called Forward Bias
 Alternating current reverses polarity all the time …..
The diode only allows it to flow in one direction.
 Testing diodes with multi-meter:
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A good Diode shows LOW resistance (ohms) in one
direction and infinitely high in the opposite direction
Rectifier Circuits
 Convert
AC current to DC current: since
electricity only flows in one direction
through diode and it is restricted in the
opposite direction.
 The result is a pulsating DC current
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(the gap between pulses is the half of the
AC cycle that is blocked)
Rectifier Circuit
Zener Diodes
 Only
allows one way flow of electricity
(just like a standard diode)
 Difference is that it conducts electricity in
the Reverse Biased direction
 It is able to maintain a steady voltage
 Often used in voltage regulation circuits
Light-Emitting Diodes (LEDs)
 Can
be produced in many colors
 Cathode (attached to negative side of
circuit) is shorter and indicated by a flat
spot on the base of the LED
 Many uses: Flashlights, headlights, LED
displays on digital readouts, etc.
 Do not produce heat (wasted energy) so
they are more efficient than
incandescent bulbs
Transistors
A
solid-state switching device (no moving
parts)
 Bipolar Transistors: three connectors
(emitter, base and collector
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Current flows between the emitter and
collector
Current is “switched” on or off by applying
current to the base.
 Can
also be used for amplification Small
current applied to B controls larger flow
through E/C
Bipolar Transistors
Field Effect Transistors
 Similar
to Bipolar transistors but…..
 Cheaper to make
 Can carry more voltage than Bipolar
 Two types:
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MOSFET: metal-oxide semiconductor field
effect transistor (may have 4th terminal)
JFET: Junction field effect transmitter (three
terminals
Field Effect Transmitters
Integrated Circuits
A
collection of electronic circuits
(indistinguishable to the naked eye)
etched into a thin layer of silicon and
installed into a plastic or ceramic housing
 Housing contains series of pins that allow
the IC to be installed into a base called a
“socket”
Integrated Circuits
 Used
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for:
Counting functions
Timing functions
Logic Functions (and, or, not)
Two types (TTL & CMOS)
Integrated Circuit
 CMOS
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Complimentary
Metal Oxide
Semiconductor
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Works with up to 18V
Easily damaged by
static electricity
(con)
Very little current
draw (pro)
Identified by
numbers starting
with “4”
 TTL
– Transistortransistor logic –
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works on low
voltage (5V or less)
Not damaged by
static electricity
(pro)
Has a high current
draw (con)
Identified by
numbers starting
with “74”
Uses for ICs
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7448-Decoder drivers for 7 pin leds
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741-operational amplifier (op-amp)- increase AC
or DC signal by up to 100,000 times
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Radios, TV, or any sound outputting device
555 (CMOS technology)
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Digital readouts on clocks, watches, etc
Monostable applications – turns on for a given
time (seatbelt light on your dashboard)
Astable applications – blinking lights (indicators)
556 – two 555 combined can do both functions
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Blinks for a fixed period of time then turns off
Fuses and Circuits
 Protect
electronic circuits form excessive
current flow (amps)
 Both open circuit in case of excessive
loads
 Breakers can be reset
 Fuses melt and must be replaced
 Must be sized properly to protect
components
Circuit Boards and Solderless
Breadboards
 Platform
for electronic circuits
 Copper paths make the connections
between components
 Solderless breadboards do the same and
components can be easily installed or
removed
Schematic Diagrams Symbols