This document provides information on basic electronics components including semiconductors, diodes, transistors, and light-emitting diodes (LEDs). It discusses how semiconductors like silicon can have their conductivity controlled and how adding impurities creates N-type and P-type materials. Diodes, transistors, and other components are formed using PN junctions in silicon. Diodes allow current to pass in one direction, while transistors can act as switches or amplifiers. LEDs emit light when forward biased and are used as indicators.
Semiconductor materials and pn junction by sarmad balochSarmad Baloch
Semiconductor materials and pn junction by sarmad baloch
I AM SARMAD KHOSA
BSIT (5TH A)
(ISP)
FACEBOOK PAGLE::
https://www.facebook.com/LAUGHINGHLAUGHTER/
YOUTUBE CHANNEL:::
https://www.youtube.com/channel/UCUjaIeS-DHI9xv-ZnBpx2hQ
The attached narrated power point presentation discusses the different types of active components used in electronics engineering and the methods to identify active electronic components. The material will be useful for KTU first year B Tech students who prepare for the subject EST 130, Part B, Basic Electronics Engineering.
Semiconductor materials and pn junction by sarmad balochSarmad Baloch
Semiconductor materials and pn junction by sarmad baloch
I AM SARMAD KHOSA
BSIT (5TH A)
(ISP)
FACEBOOK PAGLE::
https://www.facebook.com/LAUGHINGHLAUGHTER/
YOUTUBE CHANNEL:::
https://www.youtube.com/channel/UCUjaIeS-DHI9xv-ZnBpx2hQ
The attached narrated power point presentation discusses the different types of active components used in electronics engineering and the methods to identify active electronic components. The material will be useful for KTU first year B Tech students who prepare for the subject EST 130, Part B, Basic Electronics Engineering.
Introduction to Semiconductor Devices.
In modern world no other technology permeates every nook and cranny of our existence as does electronics.
Application of electronics are : Televisions, radios, stereo equipment, computers, scanners, electronic control systems (in cars for example) etc.
Electronics and Communication Engineering is the Branch of Engineering. Electronics and Communication Engineering field requires an understanding of core areas including Engineering Graphics, Computer Programming,Electronics Devices and Circuits-I, Network Analysis, Signals and Systems, Communication Systems, Electromagnetics Engineering, Digital Signal Processing, Embedded Systems, Microprocessor and Computer Architecture. Ekeeda offers Online Mechanical Engineering Courses for all the Subjects as per the Syllabus. Visit : https://ekeeda.com/streamdetails/stream/Electronics-and-Communication-Engineering
Introduction to Semiconductor Devices.
In modern world no other technology permeates every nook and cranny of our existence as does electronics.
Application of electronics are : Televisions, radios, stereo equipment, computers, scanners, electronic control systems (in cars for example) etc.
Electronics and Communication Engineering is the Branch of Engineering. Electronics and Communication Engineering field requires an understanding of core areas including Engineering Graphics, Computer Programming,Electronics Devices and Circuits-I, Network Analysis, Signals and Systems, Communication Systems, Electromagnetics Engineering, Digital Signal Processing, Embedded Systems, Microprocessor and Computer Architecture. Ekeeda offers Online Mechanical Engineering Courses for all the Subjects as per the Syllabus. Visit : https://ekeeda.com/streamdetails/stream/Electronics-and-Communication-Engineering
Truckers Insurance Hq provides insurance cover for all types of Camper Trailers. Get a truck and trailer insurance quote now with us and save more. For more details, Visit: www.truckersinsurancehq.com
HMIS is an integrated Hospital management system, which addresses All requirements of hospitals. It is a powerful, flexible and easy to use application designed and developed to convey real conceivable benefits to hospitals and clinics which reduce the paper overload.
Penjelasan tentang kitab suci, hari raya, sikap sembahyang, tempat ibadah, konsep keselamatan, konsep keTuhanan, dan permasalahan yang dihadapi oleh sebagian umat Hindu.
Electrical current, voltage, resistance, capacitance, and inductance are a few of the basic elements of electronics and radio. Apart from current, voltage, resistance, capacitance, and inductance, there are many other interesting elements to electronic technology. ... Use Electronics Notes to learn electronics online.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Saudi Arabia stands as a titan in the global energy landscape, renowned for its abundant oil and gas resources. It's the largest exporter of petroleum and holds some of the world's most significant reserves. Let's delve into the top 10 oil and gas projects shaping Saudi Arabia's energy future in 2024.
Hierarchical Digital Twin of a Naval Power SystemKerry Sado
A hierarchical digital twin of a Naval DC power system has been developed and experimentally verified. Similar to other state-of-the-art digital twins, this technology creates a digital replica of the physical system executed in real-time or faster, which can modify hardware controls. However, its advantage stems from distributing computational efforts by utilizing a hierarchical structure composed of lower-level digital twin blocks and a higher-level system digital twin. Each digital twin block is associated with a physical subsystem of the hardware and communicates with a singular system digital twin, which creates a system-level response. By extracting information from each level of the hierarchy, power system controls of the hardware were reconfigured autonomously. This hierarchical digital twin development offers several advantages over other digital twins, particularly in the field of naval power systems. The hierarchical structure allows for greater computational efficiency and scalability while the ability to autonomously reconfigure hardware controls offers increased flexibility and responsiveness. The hierarchical decomposition and models utilized were well aligned with the physical twin, as indicated by the maximum deviations between the developed digital twin hierarchy and the hardware.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
(CNN)s, to adversarial attacks and presents a proactive training technique designed to counter them. We
introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
When combined with 3D convolution and deep curriculum learning optimization (CLO), itsignificantly improves
the immunity of models against localized universal attacks by up to 40%. We evaluate our proposed approach
using contemporary CNN architectures and the modified Canadian Institute for Advanced Research (CIFAR-10
and CIFAR-100) and ImageNet Large Scale Visual Recognition Challenge (ILSVRC12) datasets, showcasing
accuracy improvements over previous techniques. The results indicate that the combination of the volumetric
input and curriculum learning holds significant promise for mitigating adversarial attacks without necessitating
adversary training.
2. Semiconductor —I
• Materials that permit flow of electrons are called
conductors (e.g., gold, silver, copper, etc.).
• Materials that block flow of electrons are called
insulators (e.g., rubber, glass, Teflon, mica, etc.).
• Materials whose conductivity falls between those
of conductors and insulators are called
semiconductors.
• Semiconductors are “part-time” conductors
whose conductivity can be controlled.
germanium
Semiconductors
silicon
3. Semiconductor —II
• Silicon is the most common material used to build semiconductor devices.
• Si is the main ingredient of sand and it is estimated that a cubic mile of seawater
contains 15,000 tons of Si.
• Si is spun and grown into a crystalline structure and cut into wafers to make
electronic devices.
4. Semiconductor —III
• Atoms in a pure silicon wafer contains four electrons in outer orbit (called valence
electrons).
– Germanium is another semiconductor material with four valence electrons.
• In the crystalline lattice structure of Si, the valence electrons of every Si atom are
locked up in covalent bonds with the valence electrons of four neighboring Si atoms.
– In pure form, Si wafer does not contain any free charge carriers.
– An applied voltage across pure Si wafer does not yield electron flow through the wafer.
– A pure Si wafer is said to act as an insulator.
• In order to make useful semiconductor devices, materials such as phosphorus (P) and
boron (B) are added to Si to change Si’s conductivity.
4 valence electrons
5. N-Type Silicon
• Pentavalent impurities such as phosphorus, arsenic, antimony, and bismuth have 5
valence electrons.
• When phosphorus impurity is added to Si, every phosphorus atom’s four valence
electrons are locked up in covalent bond with valence electrons of four neighboring
Si atoms. However, the 5th valence electron of phosphorus atom does not find a
binding electron and thus remains free to float. When a voltage is applied across the
silicon-phosphorus mixture, free electrons migrate toward the positive voltage end.
• When phosphorus is added to Si to yield the above effect, we say that Si is doped
with phosphorus. The resulting mixture is called N-type silicon (N: negative charge
carrier silicon).
• The pentavalent impurities are referred to as donor impurities.
5 valence electrons
6. P-Type Silicon —I
• Trivalent impurities e.g., boron, aluminum, indium, and gallium have 3 valence
electrons.
• 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. However, a
vacant spot “hole” is created within the covalent bond between one boron atom and
a neighboring Si atom. The holes are considered to be positive charge carriers.
When a voltage is applied across the silicon-boron mixture, a hole moves toward the
negative voltage end while a neighboring electron fills in its place.
• When boron is added to Si to yield the above effect, we say that Si is doped with
boron. The resulting mixture is called P-type silicon (P: positive charge carrier
silicon).
• The trivalent impurities are referred to as acceptor impurities.
3 valence electrons
7. P-Type Silicon —II
• The hole of boron atom points towards the negative terminal.
• The electron of neighboring silicon atom points toward
positive terminal.
• The electron from neighboring silicon atom falls into the
boron atom filling the hole in boron atom and creating a “new”
hole in the silicon atom.
• It appears as though a hole moves toward the negative
terminal!
8. Diode
•A diode is a 2 lead semiconductor that acts as a one way gate to electron flow.
– Diode allows current to pass in only one direction.
•A pn-junction diode is formed by joining together n-type and p-type silicon.
•In practice, as the n-type Si crystal is being grown, the process is abruptly altered to
grow p-type Si crystal. Finally, a glass or plastic coating is placed around the joined
crystal.
•The p-side is called anode and the n-side is called cathode.
•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.
–In a forward-biased diode current is allowed to flow through the device.
•When potential at anode is smaller than the potential at cathode, the diode is said to
be reverse biased. In a reverse-biased diode current is blocked.
+ - + -
9. 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 .
• When water pressure is from right to left, the gate is pressed against the solid stop
and no water is allowed to flow.
• Spring restoring force is analogous to 0.6V needed to forward bias a Si diode.
10. 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. The
electrons and holes
combine causing the
current to pass through
the diode. When a diode
is arranged in this way, it
is said to be forward-
biased.
Forward-biased (“open door”)
Repels holes
Repels electrons
11. Diode: How it Works—II
• A diode’s one-way gate feature does not work all the time.
• Typically for silicon diodes, an applied voltage of 0.6V or greater is needed,
otherwise, the diode will not conduct.
• This feature is useful in forming a voltage-sensitive switch.
• I-V characteristics for silicon and germanium diodes is shown below.
12. Diode: How it doesn’t work
• When a diode is
connected to a battery as
shown, holes in the n-
side are forced to the
left while electrons in
the p-side are forced to
the right. This results in
an empty zone around
the pn- junction that is
free of charge carries
creating a depletion
region. This depletion
region acts as an
insulator preventing
current from flowing
through the diode.
When a diode is
arranged in this way, it
is said to be reverse-
biased. Reverse-biased (“closed door”)
Attracts holes Attracts electrons
13. Diode Applications —Half Wave Rectifier
•Diode converts ac input voltage to a pulsed dc output voltage.
•Whenever the ac input becomes negative at diode’s anode, the diode blocks current
flow.
– o/p voltage become zero.
•Diode introduces a 0.6V drop so o/p peak is 0.6V smaller than the i/p peak.
•The o/p frequency is same as the i/p frequency.
Vin
14. Diode Applications —Full Wave Rectifier
• A full-wave rectifier does not block negative swings in the i/p voltage, rather it
transforms them into positive swings at the o/p.
• To gain an understanding of device operation, follow current flow through pairs of
diodes in the bridge circuit.
• It is easily seen that one pair (D3-Rout-D2) allows current flow during the +ve half
cycle of Vin while the other pair (D4-Rout-D1) allows current flow during the -ve half
cycle of Vin.
– o/p voltage peak is 1.2V below the i/p voltage peak.
– The o/p frequency is twice the i/p frequency.
D1 D3
D2 D4
15. Diode Applications —AC2DC Power Supply
•An AC2DC power supply
is built using a transformer
and a full-wave rectifier.
•Transformer is used to
step down the voltage i/p.
•Rectifier converts AC to
pulsed DC.
•A filter capacitor is used
to smooth out the pulses.
•Capacitor must be large
enough to store sufficient
charge so as to provide a
steady current supply to the
load:
f is rectified signal’s
frequency (120Hz).
1/LoadR C f
16. Transistor
• A three lead semiconductor device that acts as:
– an electrically controlled switch, or
– a current amplifier.
• Transistor is analogous to a faucet.
– Turning faucet’s control knob alters the flow rate of water coming out from the faucet.
– A small voltage/current applied at transistor’s control lead controls a larger current flow
through its other two leads.
Water in
Water out
17. 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 MOSFETJFET
18. BJT Types
• NPN and PNP.
– NPN: a small input current and a positive voltage applied @ its base (with VB>VE)
allows a large current to flow from collector to emitter.
– PNP: a small output current and a negative voltage @ its base (with VB<VE) allows a
much larger current to flow from emitter to collector.
19. NPN BJT: How it works — I
• When no voltage is applied at
transistor’s base, electrons in the
emitter are prevented from passing
to the collector side because of the
pn junction.
• If a negative voltage is applied to
the base, things get even worse as
the pn junction between the base
and emitter becomes reverse-
biased resulting in the formation of
a depletion region that prevents
current flow.
20. NPN BJT: How it works — II
• If a positive voltage (>0.6V) is
applied to the base of an npn
transistor, the pn junction between
the base and emitter becomes
forward-biased. During forward
bias, escaping electrons are drawn
to the positive base.
• 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. Increasing the base
voltage increases the emitter-to-
collector electron flow.
• Recall, positive current flow is in
the direction opposite to the
electron flow current flows from
collector to emitter.
22. NPN Transistor in a Complete Circuit —I
NPN: VB = VEOFF
•Normally OFF.
•No current passes from collector to emitter when base is not activated.
23. NPN Transistor in a Complete Circuit —II
NPN: VB > VE ON
• When VB > VE we have an operating circuit.
• Current passes from collector to emitter when base is activated.
25. JFET
• Junction field effect transistors like BJTs are three lead
semiconductor devices.
• JFETs are used as:
– electrically controlled switches,
– current amplifiers, and
– voltage-controlled resistors.
• Unlike BJTs, JFETs do not require a bias current and are controlled
by using only a voltage.
• JFETs are normally on when VG - VS = 0.
• When VG - VS 0, then JFETs become resistive to current flow
through the drain-source pair “JFETs are depletion devices.”
26. JFET Types
• Two types of JFETs:
– n-channel and p-channel.
• In n-channel JFET, a –ve voltage applied @ its gate (with VG < VS) reduces current
flow from drain to source. It operates with VD > VS.
• In p-channel JFET, a +ve voltage applied @ its gate (with VG > VS) reduces current
flow from source to drain. It operates with VS > VD.
• 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.
27. MOSFET
• Metal oxide semiconductor FET.
• Similar to JFET.
• A metal oxide insulator is placed @ the gate to obtain a high input impedance @ the
gate
– gate input impedance approx. 1014Ω.
• Use of insulator as described above yields a low gate-to-channel capacitance.
– If too much static electricity builds up on the gate, then the MOSFET may be damaged.
28. MOSFET Types
• Enhancement type:
– Normally off, thus no current flows through drain-source channel when VG = VS.
– When a voltage applied @ the gate causes VG VS the drain-source channel reduces
resistance to current flow.
• Depletion type:
– Normally on, thus maximum current flows through drain-source channel when VG = VS.
– When a voltage applied @ the gate causes VG VS the drain-source channel increases
resistance to current flow.
VG < VS VG > VSVG > VS VG < VS
Current flow increases with: Current flow decreases with:
29. Optoelectronics
Light emitting diodes Infrared detector
• In optoelectronics we deal with 2 types of electronic devices.
• Light emitting electronic devices: ones that generate electromagnetic energy under
the action of electrical field. Example: light emitting diodes (visible and infrared
light).
• Light detecting devices: ones that transform electromagnetic energy input into
electrical current/voltage. Examples: photoresistors, photodiodes, phototransistors,
etc.
31. LED 101— I
• 2 lead semiconductor device.
• Light emitting PN-junction diode.
– Visible or infrared light.
• Has polarity.
• Recall diodes act as a one way gate to current flow.
– A forward-biased PN-junction diode allows current flow from anode to cathode.
• An LED conducts and emits light when its anode is made more positive (approx.
1.4V) than its cathode.
– With reverse polarity, LED stops conducting and emitting light.
32. LED 101— II
• Similar to diodes, LEDs are current-dependent devices.
– LED brightness is controlled by controlling current through LED.
• Too little current through LED LED remains OFF.
• Small current through LED dimly lit LED.
• Large current through LED brightly lit LED.
• Too much current through LED LED is destroyed.
• A resistor placed in series with LED accomplishes current control
+
Anode
-
Cathode
LED symbol
33. LED 101—III
• Let Vs be the supply voltage.
• Let Vf be the required forward bias voltage for the
LED.
• Let I be the desired current flow through LED.
• Then, the current limiting resistance R is sized as
follow:
• If R is chosen smaller than the above value, a
larger current will flow through the LED.
– LEDs can handle only limited current (varies from
20mA to 100mA).
– If current through LED is larger than the maximum
allowed value, than the LED will be damaged.
Vs
Vf
VRI
R
R s f
s fR
V V V
V VV
R
I I
34. Visible-Light LED
• Inexpensive and durable.
• Typical usage: as indicator lights.
• Common colors: green (~565nm), yellow (~585nm), orange (~615nm), and red
(~650nm).
• Maximum forward voltage: 1.8V.
• Typical operating currents: 1 to 3mA.
• Typical brightness levels: 1.0 to 3.0mcd/1mA to 3.0mcd /2mA.
• High-brightness LEDs exist.
– Used in high-brightness flashers (e.g., bicycle flashers).
35. Blinking LED
• Contain a miniature integrated circuit that causes LED to flash from 1 to 6 times/second.
• Typical usage: indicator flashers. May also be used as simple oscillators.
36. Tricolor LED
• Two LEDs placed in parallel facing opposite directions.
• One LED is red or orange, the other is green.
• Current flow in one direction turns one LED ON while the other remains OFF due
to reverse bias.
• Current flow in the other direction turns the first LED OFF and the second LED ON.
• Rapid switching of current flow direction will alternatively turn the two LEDs ON
giving yellow light.
• Used as a polarity indicator.
• Maximum voltage rating: 3V
• Operating range: 10 to 20mA
37. 7-Segment LED Display
• Used for displaying numbers and other characters.
• 7 individual LEDs are used to make up the display.
• When a voltage is applied across one of the LEDs, a portion of the 8 lights up.
• Unlike liquid crystal displays (LCD), 7-segment LED displays tend to be more
rugged, but they also consume more power.
38. How LED Works
• The light-emitting section of an LED is made by joining n-type and p-type semiconductors
together to form a pn junction.
• 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.
• As the electrons combine with the holes, photons are emitted.
• 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.
• Often a reflector placed beneath the semiconductor is used to direct the light upward.
39. Photoresistors —I
• Light sensitive variable resistors.
• Its resistance depends on the intensity of light incident upon it.
– Under dark condition, resistance is quite high (M: called dark resistance).
– Under bright condition, resistance is lowered (few hundred ).
• Response time:
– When a photoresistor is exposed to light, it takes a few milliseconds, before it
lowers its resistance.
– When a photoresistor experiences removal of light, it may take a few seconds
to return to its dark resistance.
Symbol
40. Photoresistors —II
• Some photoresistors respond better to light that contains
photons within a particular wavelength of spectrum.
– Example: Cadmium-sulfide photoresistos respond to
light within 400-800nm range.
– Example: Lead-sulfide photoresistos respond to infrared
light.
41. How Photoresistor Works
• Special semiconductor crystal, such as cadmium sulfide or lead sulfide is used to make
photoresistors.
• 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.
• When this semiconductor is illuminated, incoming photons of light collide with the bound
electrons, stripping them from the binding atom, thus creating holes in the process.
• Liberated electrons contribute to the current flowing through the device.
42. Photoresistor Application —Light Activated Relay
• Light-sensitive voltage divider is being
used to trip a relay whenever the light
intensity change.
• Light-activated circuit:
– When the photoresistor is exposed to
light, its resistance decreases.
– Transistor’s base current and
voltage increase and if the base current
and voltage are large enough, the
collector-emitter pair of the transistor
conducts triggering the relay.
• The value of R1 in the light-activated
circuit should be around 1 KΩ but
may have to be adjusted.
• Dark-activated relay works in a similar
but opposite manner.
• R1 in the dark-activated circuit
(100KΩ) may also have to be adjusted.
• A 6 to 9-V relay with a 500Ω coil can
be used in either circuit.
Light activated relay Dark activated relay
43. Photodiode
• Photodiode is a 2 lead semiconductor device that transforms light energy to electric
current.
• Suppose anode and cathode of a photodiode are wired to a current meter.
– When photodiode is placed in dark, the current meter displays zero current flow.
– When the photodiode is expose to light, it acts a a current source, causing current flow
from cathode to anode of photodiode through the current meter.
• Photodiodes have very linear light v/s current characteristics.
– Commonly used as light meters in cameras.
• Photodiodes often have built-in lenses and optical filters.
• Response time of a photodiode slows with increasing surface area.
• Photodiodes are more sensitive than photoresistor.
Symbol
44. How Photodiode Works
• Photodiode: A thin n-type
semiconductor sandwiched with a
thicker p-type semiconductor.
• N-side is cathode, p-side is anode.
• Upon illumination, a # of photons pass
from the n-side and into the p-side of
photodiode.
– Some photons making it into p-side
collide with bound electrons within p-
semiconductor, ejecting them and
creating holes.
– If these collisions are close to the pn-
interface, the ejected electrons cross the
junction, yielding extra electrons on the
n-side and extra holes on the p-side.
– Segregation of +ve and -ve charges
leads to a potential difference across the
pn-junction.
– When a wire is connected between the
cathode and anode, a conventionally
positive current flow from the anode to
cathode
45. Photodiode Applications—Photovoltaic Current Source
• Photodiode converts light energy directly into electric current that can be
measured with meter.
• The input intensity of light and the output current are nearly linear.
46. • Solar cells are photodiodes with very large surface areas.
• Compared to usual photodiodes, the large surface area in photodiode of a
solar cell yields
– a device that is more sensitive to incoming light.
– a device that yields more power (larger current/volts).
• Solar cells yield more power.
• A single solar cell may provide up to 0.5V that can supply 0.1A when
exposed to bright light.
Solar Cell—I
48. Solar Cell Basic Operation—Power Sources
• Each solar cell produces an
open-circuit voltage from
around 0.45 to 0.5 V and may
generate as much as 0.1 A in
bright light.
• Similar to batteries, solar cells
can be combined in series or
parallel.
• Adding cells in series, yields
output voltage that is the sum
of the individual cell voltages.
• Adding solar cells in parallel,
yields an increased output
current vis-à-vis a single solar
cell.
49. Solar Cell Basic Operation—Battery Charger
• Nine solar cells placed in series can
be used to recharge two 1.5 V NiCd
cells.
• The diode is added to the circuit to
prevent the NiCd cells from
discharging through the solar cell
during times of darkness.
• It is important not to exceed the safe
charging rate of NiCd cells. To slow
the charge rate, a resistor can be
placed in series with the batteries.
50. Phototransistor
• Phototransistor is a light sensitive transistor.
• In one common type of phototransistor, the base lead of a BJT is replaced by a light
sensitive surface.
• When the light sensitive surface @ the base is kept in darkness, the collector-emitter
pair of the BJT does not conduct.
• When the light sensitive surface @ the base is exposed to light, a small amount of
current flows from the base to the emitter. The small base-emitter current controls
the larger collector-emitter current.
• Alternatively, one can also use a field-effect phototransistor (Photo FET).
• In a photo FET, the light exposure generates a gate voltage which controls a
drain-source current.
Phototransistor Photo FET
51. How Phototransistor Works
• The bipolar phototransistor resembles a
bipolar transistor that has extra large p-type
semiconductor region that is open for light
exposure.
• 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 barrier-
provided the photons are of the right
frequency/energy.
• As electrons jump from the p-region into the
lower n-region, holes are created in the p-
type semiconductor.
• The extra electrons injected into the lower n-
type 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.
52. Phototransistor Applications—Light Activated Relay
• A phototransistor is used to control the base current supplied to a power-switching
transistor that is used to supply current to a relay.
• 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.
• This allows the power-switching transistor to turns on, and current flows through the
relay, triggering it to switch states.
• The 100K pot is used to adjust the sensitivity of device by controlling current flow
through the phototransistor.
53. Phototransistor Applications—Dark Activated Relay
• A phototransistor is used to control the base current supplied to a power-switching
transistor that is used to supply current to a relay.
• When light is removed from the phototransistor, the phototransistor turns off,
allowing more current to enter into the base of the power-switching transistor.
• This allows the power-switching transistor to turns on, and current flows through
the relay, triggering it to switch states.
• The 100K pot is used to adjust the sensitivity of device by controlling current flow
through the phototransistor.
54. Phototransistor Applications—Tachometer
• A phototransistor is being used as a frequency counter or tachometer.
• A rotating disk is connected to a rotating shaft. The rotating disk has one hole in it.
• For the given setup, the disk will allow light to pass through the hole once every
revolution.
• The light passing through the disk triggers the phototransistor into conduction.
• A frequency counter is used to count the number of electrical pulses generated.