Download ELE2 - FENC

GCSE
REVISION NOTES
Dangers of Electricity
• An electric current can cause:
– Electric shock, muscle spasms
– The heart may be stopped
– Burning
• Do NOT touch the casualty until the
electricity is disconnected
• Keep the casualty warm
• Get assistance
Preventing Accidents
• Never work alone
• Carry out a risk assessment for all
activities
• Know how to summon help
• Do not touch the inside of electrical
equipment for some time after it is
switched off
– May be hot
– Capacitors may hold a lethal charge
Protective Measures
• Circuit breakers
– Thermal
– Magnetic
– Fuse – 3A <700W
13A>700W
• Transformer
– Primary and secondary are isolated
– Provides safe low voltage from the
mains
Three Pin Mains Plug
earth
(green & yellow)
neutral
(blue)
3
A
M
P
fuse
live
(brown)
cable clamp
cable
©IKES0902
Systems
FEEDBACK
INPUT
PROCESS
OUTPUT
©IPK01
• Complex systems broken down into
sub-systems.
• Identify sub-systems in circuit
diagrams.
Processes and Concepts
•
•
•
•
•
Timing
Amplifying
AND, OR, NOT
NAND, NOR
Memorising
•
•
•
•
•
•
•
•
Bit
Byte, KB, MB, GB
Address
Data
Read
Write
Hardware
Software
Flow Charts
No
START
END
INPUT
OUTPUT
PROCESS
COMPARE
Yes©ikes1001
• Used to determine the sequence of
operations required
• Aids logical thought
Logic Gates
A
INPUTS
A
B
OUTPUT
AND
B
OUT
0
0
0
1
0
0
1
1
0
1
0
INPUTS
A
B
OUTPUT
OR
1
A
B
OUT
0
0
1
1
0
1
0
1
1
1
0
1
©IPK01
INPUT
A
OUTPUT
NOT
A
OUT
0
1
1
0
©IPK01
©IPK01
INPUTS
A
B
OUTPUT
EX-OR
A
B
OUT
0
0
1
1
0
1
0
1
1
0
0
1
©IPK01
• NOT, AND, OR, NAND, NOR, EX-OR
• Truth tables – every combination of inputs.
D-Type Flip-Flop
D
S Q
CK D Q Q
0 0 Q Q
R Q
0 1 Q Q
 0 0 1
 1 1 0
>CK
• S sets Q to 1, R resets Q to 0. Not dependent on
the state of the clock, CK.
• On the rising edge of CK, Q is set to the logic
state of D.
Frequency Divider
• To make a flip-flop
D
Q
toggle:output
>CK
• Both Set and
input
Reset are
Q
R
connected to 0
• D is connected to Q
• The D input is then always opposite to Q and so
toggling occurs on each successive clock pulse.
S
input
Q
©IKES0902
4017 counter
5
1
+Vs
1
• 10 decoded outputs
0
2
6
input
7
0
R
4
0
1
7
0V
2
3
©IKES0902
CI
Carry
9
4
3
1
CK
©IKES0902
8
555 Monostable
+Vs
R
+Vs
RESET
T  1.1  R  C
OUT PUT
T RIGGER
T HRESHOLD
DISCHARGE
Vin
Vout
GND CONT ROL
C
10nF
0V
©IPK01
•
•
•
•
•
•
When the TRIGGER input goes below 1/3Vs
OUTPUT goes high and DISCHARGE switches off
C charges through R
Until capacitor voltage =2/3Vs (THRESHOLD voltage)
OUTPUT goes low and DISCHARGE switches on
Capacitor discharged.
555 astable
tH  0.7R1  R 2C
+Vs
R1
+Vs
RESET
tL  0.7 R2 C
DISCHARGE
OUT PUT
R2
T RIGGER
T HRESHOLD
GND CONT ROL
C
Vout
10nF
0V
•
•
•
•
•
•
•
•
©IPK01
1.44
f
R1  2 R 2C
When first switched on, TRIGGER is less than 1/3Vs
OUTPUT goes high, DISCHARGE switches off
Capacitor charges through R1 and R2
Until capacitor voltage = 2/3Vs (THRESHOLD)
OUTPUT goes low, DISCHARGE switches on
Capacitor discharges through R2
Until capacitor voltage = 1/3Vs (TRIGGER)
OUTPUT goes high, process repeats
Operational Amplifier
+Vs
+
V+
V–
-Vs
Differential amplifier
• Large input resistance
109
• Large open-loop voltage
gain, A,  106
V
out
0V • Low output resistance 
100
• Frequency compensated
• Gain-bandwidth product
Vout  A(V  V)
Comparator
+Vs
R1
R2
V1
V2
+
–
V1 V 2  Vout   Vs
V 2 V1  Vout   Vs
R3
©IPK01
0V
• Can be used as a one-bit analogue to
digital converter
The Audio Amplifier
• LM380, LM386, TBA820
• Bandwidth
Vout
Voltage gain (Gv) 
Vin
• At least half of its rated power
• At least 70% of its rated voltage gain
voltage
gain
100
80
70
60
40
bandwidth
20
10
10
10 2
10 3
10
4
10
5
10
6
frequency / Hz
Prefixes
• giga
• mega
• kilo
×1,000,000,000
×1,000,000
×1,000
(G)
(M)
(k)
GHz
MHz, M
kHz, k, kV
• milli
• micro
• nano
×0.001
×0.000 001
×0.000 000 001
(m)
()
(n)
mV, mA, mW
V, A, W, F
nF
• pico
×0.000 000 000 001
(p)
pF
Voltage and Current
• Voltage ACROSS object – Volts
• Current THROUGH object – Amps
• Power = Voltage x Current – Watts
• Resistance = Voltage/Current - Ohms
V
I
R
Alternating Current
voltage or current
peak value
• Sine wave
rms value
• Continuously
reverses direction
0
amplitude
time
1 cycle
• Peak value = 1.4 x rms value
• Frequency = 1 / time period
©IKES0902
Series and Parallel
• Series:-
1.4 k
– Current is the same
– Voltage is shared
2.2 k
3.7 k
©IPK01
• Parallel:– Current is shared
– Voltage is the same
10k
5k
©IPK01
Resistors
• In series – R T  R1  R 2  R 3
• In parallel –
1
RT
• Colour Code
• BS1852
• Preferred values
• Tolerance

1
R1

1
R2
Diodes
anode
cathode
-40
cathode
symbol
component outline
current/mA
10
current/mA
10
reverse bias
-60
breakdown
anode
-20
Figure 4.5(a)
8
forward bias
reverse bias 8
6
6
4
4
2
2
0
+20
voltage/V
-1
forward bias
0
1
voltage/V
©IPK01
Figure 4.5(b)
• Conventional current flow.
• Allows current to pass in one direction.
• 0.7V across a forward biased silicon diode
Rectification
Half wave
diode
+
Vin
Vout
©IKES0902
V
V
load
time
time
input waveform
_
output waveform
©IKES0902
A
D1
V
time
D4
D2
D3
+ Full wave
V
B
load
Vout
_
time
©IKES0902
LEDs
+Vs
R
0V
0V
©IPK01
• Find the voltage
across R.
• Note the maximum
current through the
LED
• Calculate R
• Choose the next
largest preferred
value
Resistive Input Devices
• LDR
resistance
/ ohms 7
10
10
6
10
5
10
4
10 3
10
©IPK01
2
0.1
1
10
10 2 10 3 10 4
illumination/lux
• Thermistor
resistance
/ ohms
10
5
10
4
10 3
10 2
10
©IPK01
– as light level
increases, the
resistance
decreases
– Log-log graphs.
0
20
40 60 80 100o
temperature / C
– As the temperature
increases, the
resistance
decreases
– Log-lin graphs
Voltage Dividers
I
 R2
V
in
V out 
R1  R 2
R1
Vin
R2
Vout
©IPK01
• This formula is not
on the data sheet!
Transistors and MOSFETs
n-channel MOSFET
npn transistor
collector
drain
large
current
base
large
current
gate
small current
emitter
©IPK01
Vgs
source
©IPK01
• MOSFETs
• Very high input resistance
• Voltage operated
• Transistors
• Low input resistance – needs base series resistor
• Current operated
Output devices
+Vs
• Motor
• Relay
• solenoid
protection
diode
input
0V
©IPK01
• Use diode with inductive devices
• To remove large induced voltage
• Diode protects semiconductor when the
device is switched OFF
Three Terminal Regulators
top view
• Provides
constant output
voltage
• 7805 = 5V +Vin
• 7812 = 12V
• 7815 = 15V
metal tab
output
common
input
mounting hole
78xx
470nF
©IKES0902
+Vout
100nF
1 - 10k
0V
0V
©IKES0902
Audio Systems
• A domestic hi-fi installation:
– Tuner
– Amplifier
– Microphone
– Loudspeaker
– Minidisk
– MP3 player
– CD player
– Cassette tape recorder
The Simple Receiver
aerial
•
•
•
•
•
rf tuned
circuit
demodulator
af
amplifier
loud
speaker
Aerial/earth – changes em waves into electrical signal
Tuned circuit – filters out required signals
Demodulator – removes bottom half of the AM signal
Rf filter – removes the remaining rf signal
Output – recovered information signal
The Simple Receiver
-Limitations
• Poor selectivity:
– Only one tuned circuit
– Increase the number of tuned circuits
– Difficult to tune several tuned circuits together
• Poor sensitivity:
– No amplification – uses energy received by the
aerial
– Add rf amplifier
– Add af amplifier
Amplitude Modulation (AM)
• Frequency
constant
• Amplitude
varies
• Broadcast
bandwidth is
9kHz
• Long and
medium wave
bands
Voltage
Carrier
time
Voltage
Information
time
Voltage
Amplitude
Modulated
Carrier
time
©ikes1201
Frequency Modulation (FM)
Voltage
• Constant
amplitude
• Varying
frequency
• Broadcast
bandwidth
is 100kHz
• VHF wave
band
Carrier
time
Voltage
Information
time
Voltage
Frequency
Modulated
Carrier
time
©ikes1201