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Title: basic eletrical engineering
Description: basics of electrical components
Description: basics of electrical components
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Basic Electronics
Semiconductor —I
•
Materials that permit flow of electrons are called
conductors (e
...
, gold, silver, copper, etc
...
g
...
•
Materials whose conductivity falls between those
of conductors and insulators are called
semiconductors
...
germanium
Semiconductors
silicon
Semiconductor —II
•
Silicon is the most common material used to build semiconductor devices
...
•
Si is spun and grown into a crystalline structure and cut into wafers to make
electronic devices
...
– Germanium is another semiconductor material with four valence electrons
...
– In pure form, Si wafer does not contain any free charge carriers
...
– A pure Si wafer is said to act as an insulator
...
4 valence electrons
N-Type Silicon
•
Pentavalent impurities such as phosphorus, arsenic, antimony, and bismuth have 5
valence electrons
...
However, the 5th valence electron of phosphorus atom does not find a
binding electron and thus remains free to float
...
•
When phosphorus is added to Si to yield the above effect, we say that Si is doped
with phosphorus
...
•
The pentavalent impurities are referred to as donor impurities
...
g
...
When boron is added to Si, every boron atom’s three valence electrons are locked up
in covalent bond with valence electrons of three neighboring Si atoms
...
The holes are considered to be positive charge carriers
...
When boron is added to Si to yield the above effect, we say that Si is doped with
boron
...
The trivalent impurities are referred to as acceptor impurities
...
•
The electron of neighboring silicon atom points toward
positive terminal
...
•
It appears as though a hole moves toward the negative
terminal!
Diode
•A diode is a 2 lead semiconductor that acts as a one way gate to electron flow
...
•A pn-junction diode is formed by joining together n-type and p-type silicon
...
Finally, a glass or plastic coating is placed around the joined
crystal
...
•When the anode and cathode of a pn-junction diode are connected to external voltage
such that the potential at anode is higher than the potential at cathode, the diode is said
to be forward biased
...
•When potential at anode is smaller than the potential at cathode, the diode is said to
be reverse biased
...
+
-
+
-
Water Analogy of Diodes
•
When water pressure on left overcomes the restoring force of spring, the gate is
opened and water is allowed to flow
...
•
Spring restoring force is analogous to 0
...
Diode: How it Works —I
•
When
a
diode
is
connected to a battery as
shown, electrons from
the n-side and holes from
the p-side are forced
toward the center by the
electrical field supplied
by the battery
...
When a diode
is arranged in this way, it
is said to be forwardbiased
...
Typically for silicon diodes, an applied voltage of 0
...
This feature is useful in forming a voltage-sensitive switch
...
Diode: How it doesn’t work
•
When a diode is
connected to a battery as
shown, holes in the nside are forced to the
left while electrons in
the p-side are forced to
the right
...
This depletion
region acts as an
insulator
preventing
current from flowing
through
the
diode
...
Attracts holes
Attracts electrons
Reverse-biased (“closed door”)
Diode Applications —Half Wave Rectifier
•Diode converts ac input voltage to a pulsed dc output voltage
...
– o/p voltage become zero
...
6V drop so o/p peak is 0
...
•The o/p frequency is same as the i/p frequency
...
To gain an understanding of device operation, follow current flow through pairs of
diodes in the bridge circuit
...
– o/p voltage peak is 1
...
– The o/p frequency is twice the i/p frequency
...
•Transformer is used to
step down the voltage i/p
...
•A filter capacitor is used
to smooth out the pulses
...
Transistor
•
•
A three lead semiconductor device that acts as:
– an electrically controlled switch, or
– a current amplifier
...
– Turning faucet’s control knob alters the flow rate of water coming out from the faucet
...
Water out
Water in
Transistor Types: BJT, JFET, and MOSFET
•
Bipolar Junction Transistor (BJT)
– NPN and PNP
•
Junction Field Effect Transistor (JFET)
– N-channel and P-channel
•
Metal Oxide Semiconductor FET (MOSFET)
– Depletion type (n- and p-channel) and enhancement type (n- and p-channel)
BJT
JFET
MOSFET
BJT Types
•
NPN and PNP
...
– PNP: a small output current and a negative voltage @ its base (with VB
...
If a negative voltage is applied to
the base, things get even worse as
the pn junction between the base
and emitter becomes reversebiased resulting in the formation of
a depletion region that prevents
current flow
...
6V) is
applied to the base of an npn
transistor, the pn junction between
the base and emitter becomes
forward-biased
...
Some electrons exit through the
base, but because the p-type base
is so thin, the onslaught of
electrons that leave the emitter get
close enough to the collector side
that they begin jumping into the
collector
...
Recall, positive current flow is in
the direction opposite to the
electron flow current flows from
collector to emitter
...
•No current passes from collector to emitter when base is not activated
...
• Current passes from collector to emitter when base is activated
...
JFET
•
•
Junction field effect transistors like
semiconductor devices
...
•
•
•
Unlike BJTs, JFETs do not require a bias current and are controlled
by using only a voltage
...
When VG - VS 0, then JFETs become resistive to current flow
through the drain-source pair “JFETs are depletion devices
...
•
•
•
In n-channel JFET, a –ve voltage applied @ its gate (with VG < VS) reduces current
flow from drain to source
...
In p-channel JFET, a +ve voltage applied @ its gate (with VG > VS) reduces current
flow from source to drain
...
JFETs have very high input impedance and draw little or no input current
– if there is any circuit/component connected to the gate of a JFET, no current is drawn
away from or sunk into this circuit
...
Similar to JFET
...
1014Ω
...
– If too much static electricity builds up on the gate, then the MOSFET may be damaged
...
– When a voltage applied @ the gate causes VG VS the drain-source channel reduces
resistance to current flow
...
– When a voltage applied @ the gate causes VG VS the drain-source channel increases
resistance to current flow
...
Light emitting electronic devices: ones that generate electromagnetic energy under
the action of electrical field
...
Light detecting devices: ones that transform electromagnetic energy input into
electrical current/voltage
...
Light emitting diodes
Infrared detector
Light-Emitting Diodes (LEDs)
LED 101— I
•
•
2 lead semiconductor device
...
– Visible or infrared light
...
Recall diodes act as a one way gate to current flow
...
•
An LED conducts and emits light when its anode is made more positive (approx
...
4V) than its cathode
...
LED 101— II
• Similar to diodes, LEDs are current-dependent devices
...
• Too little current through LED LED remains OFF
...
• Large current through LED brightly lit LED
...
• A resistor placed in series with LED accomplishes current control
+
-
Anode
Cathode
LED symbol
LED 101—III
•
•
Vs
R
I
VR
•
•
Let Vs be the supply voltage
...
Let I be the desired current flow through LED
...
– LEDs can handle only limited current (varies from
20mA to 100mA)
...
Visible-Light LED
•
•
•
•
•
•
•
Inexpensive and durable
...
Common colors: green (~565nm), yellow (~585nm), orange (~615nm), and red
(~650nm)
...
8V
...
Typical brightness levels: 1
...
0mcd/1mA to 3
...
High-brightness LEDs exist
...
g
...
Blinking LED
• Contain a miniature integrated circuit that causes LED to flash from 1 to 6 times/second
...
May also be used as simple oscillators
...
One LED is red or orange, the other is green
...
Current flow in the other direction turns the first LED OFF and the second LED ON
...
Used as a polarity indicator
...
7 individual LEDs are used to make up the display
...
Unlike liquid crystal displays (LCD), 7-segment LED displays tend to be more
rugged, but they also consume more power
...
When the pn junction is forward-biased, electrons in the n side are excited across the pn
junction and into the p side, where they combine with holes
...
The pn-junction section of an LED is encased in an epoxy shell that is doped with light
scattering particles to diffuse light and make the LED appear brighter
...
Photoresistors —I
• Light sensitive variable resistors
...
– Under dark condition, resistance is quite high (M: called dark resistance)
...
• Response time:
– When a photoresistor is exposed to light, it takes a few milliseconds, before it
lowers its resistance
...
Symbol
Photoresistors —II
• Some photoresistors respond better to light that contains
photons within a particular wavelength of spectrum
...
– Example: Lead-sulfide photoresistos respond to infrared
light
...
When this semiconductor is placed in dark, electrons within its structure resist flow through
the resistor because they are too strongly bound to the crystal’s atoms
...
Liberated electrons contribute to the current flowing through the device
...
Light-activated circuit:
– When the photoresistor is exposed to
light, its resistance decreases
...
•
•
•
•
The value of R1 in the light-activated
circuit should be around 1 KΩ but
may have to be adjusted
...
R1 in the dark-activated circuit
(100KΩ) may also have to be adjusted
...
Light activated relay
Dark activated relay
Photodiode
•
•
Photodiode is a 2 lead semiconductor device that transforms light energy to electric
current
...
– When photodiode is placed in dark, the current meter displays zero current flow
...
•
Photodiodes have very linear light v/s current characteristics
...
•
•
•
Photodiodes often have built-in lenses and optical filters
...
Photodiodes are more sensitive than photoresistor
...
N-side is cathode, p-side is anode
...
– Some photons making it into p-side
collide with bound electrons within psemiconductor, ejecting them and
creating holes
...
– Segregation of +ve and -ve charges
leads to a potential difference across the
pn-junction
...
The input intensity of light and the output current are nearly linear
...
Compared to usual photodiodes, the large surface area in photodiode of a
solar cell yields
– a device that is more sensitive to incoming light
...
Solar cells yield more power
...
5V that can supply 0
...
Solar Cell—II
Solar Cell Basic Operation—Power Sources
•
•
•
•
Each solar cell produces an
open-circuit voltage from
around 0
...
5 V and may
generate as much as 0
...
Similar to batteries, solar cells
can be combined in series or
parallel
...
Adding solar cells in parallel,
yields an increased output
current vis-à-vis a single solar
cell
...
5 V NiCd
cells
...
It is important not to exceed the safe
charging rate of NiCd cells
...
Phototransistor
•
•
•
•
•
Phototransistor is a light sensitive transistor
...
When the light sensitive surface @ the base is kept in darkness, the collector-emitter
pair of the BJT does not conduct
...
The small base-emitter current controls
the larger collector-emitter current
...
• In a photo FET, the light exposure generates a gate voltage which controls a
drain-source current
...
When photons from a light source collide
with
electrons
within
the
p-type
semiconductor, they gain enough energy to
jump across the pn-junction energy barrierprovided the photons are of the right
frequency/energy
...
The extra electrons injected into the lower ntype slab are drawn toward the positive
terminal of the battery, while electrons from
the negative terminal of the battery are draw
into the upper n-type semiconductor and
across the np junction, where they combine
with the holes, the net result is an electrons
current that flows from the emitter to the
collector
...
When light comes in contact with the phototransistor, the phototransistor turns on,
allowing current to pass from the supply into the base of the power-switching
transistor
...
The 100K pot is used to adjust the sensitivity of device by controlling current flow
through the phototransistor
...
When light is removed from the phototransistor, the phototransistor turns off,
allowing more current to enter into the base of the power-switching transistor
...
The 100K pot is used to adjust the sensitivity of device by controlling current flow
through the phototransistor
...
• A rotating disk is connected to a rotating shaft
...
• For the given setup, the disk will allow light to pass through the hole once every
revolution
...
• A frequency counter is used to count the number of electrical pulses generated
Title: basic eletrical engineering
Description: basics of electrical components
Description: basics of electrical components