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Transcript
Characteristics, Structures, and
Applications






Description of LED and Infrared LED
Schematic Symbol
Structure
Function and Characteristics
Application and Operation
Actual Component Figure
LED is a semiconductor chip that
generates light when current is
applied to it, which is very
different from any other technology
currently used in lighting. There
are also different types of LED
emitters that have different
characteristics that affect their
applicability in lighting.

An infrared light-emitting diode (IRLED) is a
type of electronic device that
emits infrared light not visible to the naked
eye. An infraredLED operates like a
regular LED, but may use different materials
to produce infrared light.

LED is visible than Infrared LED

Infrared LEDs have a lower forward voltage,
and a higher rated current compared to
visible LEDs. This is due to differences in the
material properties of the junction.

A typical drive current for an infrared LED
can be as high as 50 milliamps, so dropping in
a visible LED as a replacement for
an infrared LED could be a problem with
some circuit designs.
 run
very low current levels, in
the tens of Milliamps
 commonly
LEDs”
 Low
cost
referred as “indicator
 applications
(push buttons,
switches), clocks, tail lights on
cars and trucks, reader boards and
low wattage accent lighting
applications
 approximately
50% of their initial
light output within a few thousand
hours and cannot generate or
maintain enough light for use in
general lighting applications
 always
of surface mount form
factor (meaning a chip or multiple
chips on a die)
 running
hundreds of milliamps per
chip and generate a much more
useful amount of light
 far
more expensive than their low
powered LED cousin but for
“general lighting applications”
they will perform best
 main
concern with high powered
LEDs is negligible heat
die
 lead frame which houses the die
 encapsulation epoxy which
protectively surrounds the die,
and also disperses the light
 anvil
 post

 The
die is bonded with conductive
epoxy into a recess in one half of
the lead frame, called the anvil
due to its shape. The recess in
the anvil is shaped to throw the
light radiation forward. The die's
top contact is wire-bonded to the
other lead frame terminal, the
post.
 LEDs
are p-n junction devices constructed
of gallium arsenide (GaAs), gallium
arsenide phosphide (GaAsP), or gallium
phosphide (GaP). Silicon and germanium are
not suitable because those junctions
produce heat and no appreciable IR or
visible light. The junction in an LED
is forward biased and when electrons cross
the junction from the n- to the p-type
material, the electron-hole recombination
process produces some photons in the IR or
visible in a process
called electroluminescence. An exposed
semiconductor surface can then emit light.
LED
is a semiconductor chip doped,
with impurities to create a p-n
junction. The current flows from
the p-side, or anode, to the nside, or cathode, but not in the
reverse direction. Charge carriers
electrons and holes that flow into
the junction from electrodes with
different voltages (3 to 3.9VDC).
 When
an electron meets a hole, it
falls into a lower energy level,
and releases energy in the form of
a photon (Photon=light). The
wavelength of the light emitted,
and therefore its color, depends
on the band gap energy of the
materials forming the p-n
junction.
 AV instruments such as Audio, TV, VCR,

CD, DVD, MD etc.
 Home appliances such as Air conditioner,
Fan etc.
 The other equipments with wireless
remote control.
 CATV set top boxes.
 Multi-media Equipment.
Sensors and light barrier systems for long
distances





indication lights
computer components
watches
medical devices
tanning equipment

The simplest way to operate an LED is
to apply a voltage source across it
with a resistor in series. The LED
emits constant-intensity light as long
as the operating voltage (VB) remains
constant (although the intensity
decreases with increasing ambient
temperature). You can vary the light
intensity as required by changing the
resistor value.

Note that the voltage
drop across an LED
increases with forward
current. Assuming that
a single green LED
with 10mA forward
current should have a
constant operating
voltage of 5V, the
series resistor
RV equals (5V VF,10mA)/10mA = 300Ω.