Analog Electronics ppt on Photo Diodes and LED by Being topper

1. Photodiode and LIGHT EMITTING DIODE
Presentation by JASWANT KUMAR
ROLL NO.-12
IT(3rd SEM.)
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2. About
LEDs
(1/2)
• A light emitting diode (LED) is essentially a PN junction optosemiconductor that emits a monochromatic (single color) light
when operated in a forward biased direction.
• LEDs convert electrical energy into light energy.
LED SYMBOL
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3. ABOUT LEDS (2/2)
• The most important part of a light emitting diode (LED) is the
semi-conductor chip located in the center of the bulb as shown at
the right.
• The chip has two regions separated by a junction.
• The junction acts as a barrier to the flow of electrons between the
p and the n regions.
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4. LED CIRCUIT basic
•
In electronics, the
LED circuit is an electric
power circuit used to power a light-emitting diode
or LED. The simplest such circuit consists of a
voltage source and two components connect in
series: a current-limiting resistor (sometimes called
the ballast resistor), and an LED. Optionally, a
switch may be introduced to open and close the
circuit. The switch may be replaced with another
component or circuit to form a continuity tester.
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5. HOW DOES A LED WORK?
• Each time an electron recombines with
a positive charge, electric potential
energy is converted into
electromagnetic energy.
• For each recombination of a negative
and a positive charge, a quantum of
electromagnetic energy is emitted in
the form of a photon of light with a
frequency characteristic of the semiconductor material.
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6. Mechanism behind photon emission in LEDs?
Mechanism is “injection
Electroluminescence”.
Luminescence
part tells us that we are producing photons.
Electro part tells us that
the photons are being produced
by an electric current.
Injection tells us that
photon production is by
the injection of current carriers.
e-
e-

7. Producing photon
Electrons recombine with holes.
e-
h
CB
VB

8. e-
Energy of photon is the energy of
band gap.
CB
VB
holes

9. • When sufficient voltage is applied to the
chip across the leads of the LED,
electrons can move easily in only one
direction across the junction between the
p and n regions.
• When a voltage is applied and the current
starts to flow, electrons in the n region
have sufficient energy to move across the
junction into the p region.
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10. How Much Energy Does an LED Emit?
• The energy (E) of the light emitted by an LED is related to the
electric charge (q) of an electron and the voltage (V) required to light
the LED by the expression: E = qV Joules.
• This expression simply says that the voltage is proportional to the
electric energy
• The constant q is the electric charge of a single electron, -1.6 x 10 -19
Coulomb.
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11. Colours of LEDs
• LEDs are made from gallium-based
crystals that contain one or more
additional materials such as phosphorous
to produce a distinct color.
• Different LED chip technologies emit
light in specific regions of the visible
light spectrum and produce different
intensity levels.
• LEDs are available in red, orange, amber, yellow, green, blue and white.
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12. LED Characteristics & Colours
• One of the major characteristics of an LED is
its colour. The different LED characteristics
have been brought about by a variety of
factors, in the manufacture of the LED. The
semiconductor make-up is a factor, but
fabrication technology and encapsulation
also play major part of the determination of
the LED characteristics.
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13. Some Types of LEDs
Bargraph
7-segment
Starburst
Dot matrix
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14. LED Performance
LED performance is based on a few primary characteristics:
•
•
•
•
•
•
•
Color
White light
Intensity
Eye safety information
Visibility
Operating Life
Voltage/Design Current
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15. Applications
•
Sensor Applications
• Mobile Applications
• Sign Applications
• Automative Uses
• LED Signals
• Illuminations
• Indicators
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16. 2. PHOTODIODE
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17. What is photodiode
Symbol of photodiode
Photodiodes are semiconductor light sensors
that generate a current or voltage when the
P-N junction in the semiconductor is
illuminated by light
A photodiode is a type of photodetector
capable of converting light into either current
or voltage, depending upon the mode of
operation. The common, traditional solar cell
used to generate electric solar power is a
large area photodiode.
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18. Principle of operation
•
PHOTODIODE CROSS SECTION
A photodiode is a p-n junction or PIN
structure. When a photon of sufficient
energy strikes the diode, it excites an
electron, thereby creating a free electron
(and a positively charged electron hole).
This mechanism is also known as the inner
photoelectric effect. If the absorption
occurs in the junction's depletion region, or
one diffusion length away from it, these
carriers are swept from the junction by the
built-in field of the depletion region. Thus
holes move toward the anode, and
electrons toward the cathode, and a
photocurrent is produced. This
photocurrent is the sum of both the dark
current (without light) and the light current,
so the dark current must be minimized to
enhance the sensitivity of the device.
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Photodiode P-N junction state

19. Photodiode types
•
•
•
•
PN photodiode
PIN photodiode
Schottky type photodiode
APD (Avalanche photodiode)
All of these types provide the following features and are
widely used for the detection of the intensity, position, colour
and presence of light.
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20. Features of photodiode
•
•
•
•
•
•
Excellent linearity with respect to incident light
Low noise
Wide spectral response
Mechanically rugged
Compact and lightweight
Long life
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21. APPLICATION of photodiode
 P-N photodiodes are used in similar applications to other photodetectors, such as
photoconductors, charge-coupled devices, and photomultiplier tubes. They may
be used to generate an output which is dependent upon the illumination (analog;
for measurement and the like), or to change the state of circuitry (digital; either
for control and switching, or digital signal processing).
 Photodiodes are used in consumer electronics devices such as compact disc
players, smoke detectors, and the receivers for infrared remote control devices
used to control equipment from televisions to air conditioners. For many
applications either photodiodes or photoconductors may be used. Either type of
photosensor may be used for light measurement, as in camera light meters, or to
respond to light levels, as in switching on street lighting after dark.
 Photodiodes are often used for accurate measurement of light intensity in
science and industry. They generally have a more linear response than
photoconductors.
 They are also widely used in various medical applications, such as detectors for
computed tomography .
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22. Photodiode Alarm circuit
This Photodiode based Alarm can be used to give a warning alarm when
someone passes through a protected area. The circuit is kept standby through a
laser beam or IR beam focused on to the Photodiode. When the beam path
breaks, alarm will be gets active.
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23. Working of alarm circuit
•
The circuit uses a PN Photodiode in the reverse bias mode to detect light
intensity. In the presence of Laser / IR rays, the Photodiode conducts and
provides base bias to T1. The NPN transistor T1 conducts and takes the reset
pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the
components R3, VR1 and C3. The Astable operates only when its resent pin
becomes high. When the Laser / IR beam breaks, current thorough the
Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high
and enables IC1. The output pulses from IC1 drives the speaker and alarm tone
will be generated.
A simple IR transmitter circuit is given which uses
Continuous IR rays. The transmitter can emit IR
rays up to 5 meters if the IR LEDs are enclosed
in black tubes.
IR Transmitter Circuit
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24. ::The END::
Thank you for your
Attention!