LED工作原理中英文翻译

英文原文

How Light Emitting Diodes Work

Light emitting diodes, commonly called

LEDs, are real unsung heroes in the electronics

world. They do dozens of different jobs and are found in all kinds of devices. Among other things,

they

form

the

numbers

on

digital

clocks,

transmit

information

from

remote

controls,

light

up

watches

and

tell

you

when

your

appliances

are

turned

on.

Collected

together,

they

can

form

images on a jumbo television screen or illuminate a traffic light. Basically, LEDs are just tiny light

bulbs that fit easily

into an electrical circuit. But unlike ordinary

incandescent bulbs, they don't

have a filament that will burn out, and they don't get especially hot. They are illuminated solely by

the movement of electrons in a semiconductor material, and they last just as long as a standard

transistor.

In

this

article,

we'll

examine

the

simple

principles

behind

these

ubiquitous

blinkers,

illuminating some cool principles of electricity and light in the process.

What is a Diode? A diode is the simplest sort of semiconductor device. Broadly speaking, a

semiconductor

is

a

material

with

a

varying

ability

to

conduct

electrical

current.

Most

semiconductors are made of a poor conductor that has had impurities (atoms of another material)

added to it. The process of adding impurities is called doping. In the case of LEDs, the conductor

material

is

typically

aluminum-gallium- arsenide.

In

pure

aluminum-gallium-arsenide,

all

of

the

atoms bond perfectly to their neighbors, leaving no free electrons (negatively- charged particles) to

conduct electric current. In doped material, additional atoms change the balance, either adding free

electrons

or

creating

holes

where

electrons

can

go.

Either

of

these

additions

make

the

material

more conductive. A semiconductor with extra electrons is called N-type material, since it has extra

negatively-charged

particles.

In

N-type

material,

free

electrons

move

from

a

negatively-charged

area to a positively charged area. A semiconductor with extra holes is called P-type material, since

it effectively has extra positively- charged particles. Electrons can jump from hole to hole, moving

from

a

negatively-charged

area

to

a

positively- charged

area.

As

a

result,

the

holes

themselves

appear to move from a positively- charged area to a negatively-charged area. A diode comprises a

section of N-type

material bonded to a section of P-type material, with electrodes on each end.

This

arrangement

conducts

electricity

in

only

one

direction.

When

no

voltage

is

applied

to

the

diode,

electrons

from

the N-type

material

fill

holes

from

the

P-type

material

along

the

junction

between the layers, forming a depletion zone. In a depletion zone, the semiconductor material is

returned to its original insulating state -- all of the holes are filled, so there are no free electrons or

empty spaces for electrons, and charge can't flow. To get rid of the depletion zone, you have to get

electrons

moving

from

the

N-type

area

to

the

P-type

area

and

holes

moving

in

the

reverse

direction. To do this, you connect the N-type side of the diode to the negative end of a circuit and

the P-type side to the positive end. The free electrons in the N-type material are repelled by the

negative electrode and drawn to the positive electrode. The holes in the P-type material move the

other way. When the voltage difference between the electrodes is high enough, the electrons in the

depletion

zone

are

boosted

out

of

their

holes

and

begin

moving

freely

a

result,

the

depletion zone the negative end of the circuit is hooked up to the N-type layer

and the positive end is hooked up to P-type layer, electrons and holes start moving. If the P-type

side is connected to the negative end of the circuit and the N-type side is connected to the positive

end, current will not flow. No current flows across the junction because the holes and the electrons

are each moving in the wrong direction. When the positive end of the circuit is hooked up to the

N-type layer and the negative end is hooked up to the P-type layer, the depletion zone gets bigger.

The interaction between electrons and holes has an interesting effect -- it generates light! In the

next section, we'll find out exactly why this is.

How Can a Diode Produce Light? Light is a form of energy that can be released by an atom.

It is made up of many small particle-like packets that have energy. These particles, called photons,

are the most basic units of light. Photons are released as a result of moving electrons. In an atom,

electrons

move

in

orbitals

around

the

nucleus.

Electrons

in

different

orbitals

have

different

amounts

of

energy.

Generally

speaking,

electrons

with

greater

energy

move

in

orbitals

farther

away from the nucleus. For an electron to jump from a lower orbital to a higher orbital, something

has to boost its energy level. Conversely, an electron releases energy when it drops from a higher

orbital

to

a

lower

one.

This

energy

is

released

in

the

form

of

a

photon.

A

greater

energy

drop

releases a higher- energy photon, which is characterized by a higher frequency. As we saw in the

last section, free electrons moving across a diode can fall into empty holes from the P-type layer.

This involves a drop from the conduction band to a lower orbital, so the electrons release energy

in the form of photons. This happens in any diode, but

you can only see the photons when the

diode

is

composed

of

certain

material.

The

atoms

in

a

standard

silicon

diode,

for

example,

are

arranged in such a way that the electron drops a relatively short distance. As a result, the photon's

frequency is so low that it is invisible to the human eye -- it is in the infrared portion of the light

spectrum. This isn't necessarily a bad thing, of course: Infrared LEDs are ideal for remote controls,

among other things. Visible light-emitting diodes (VLEDs), such as the ones that light up numbers

in a digital clock, are made of materials characterized by a wider gap between the conduction band

and

the

lower

orbitals.

The

size

of

the

gap

determines

the

frequency

of

the

photon

--

in

other

words,

it

determines

the

color

of

the

light. While

all

diodes

release

light,

most

don't

do

it

very

effectively. In an ordinary diode, the semiconductor material itself ends up a lot of the light energy.

LEDs are specially constructed to release a large number of photons outward. Additionally, they

are housed in a plastic bulb that concentrates the light in a particular direction.

LEDs have several advantages over conventional incandescent lamps. For one thing, they

don't have a filament that will burn out, so they last much longer. Additionally, their small plastic

bulb makes them a lot more durable. They also fit more easily into modern electronic circuits. But

the main advantage is efficiency. In conventional incandescent bulbs, the light-production process

involves generating a lot of heat. This is completely wasted energy, unless you're using the lamp

as a heater. LEDs generate very little heat, relatively speaking. A much higher percentage of the

electrical power is going directly to generating light, which cuts down on the electricity demands

considerably.

Up

until

recently,

LEDs

were

too expensive

to

use

for

most

lighting

applications.

The price of semiconductor devices has plummeted over the past decade, however, making LEDs

a

more

cost-effective

lighting

option

for

a

wide

range

of

situations.

While

they

may

be

more

expensive

than

incandescent

lights

up

front,

their

lower

cost

in

the

long

run

can

make

them

a

better buy. In the future, they will play an even bigger role in the world of technology.

TRANSIENT VOLTAGE SUPPRESSOR(TVS) Diode PRESENTATION

? High protection on sensitive mobile electronic devices

? Follow strictly to the IEC 61000

-4-2 ESD test standard

?

Using the behavior of diode P/N junction to achieve ESD protection

What are Transient Voltages?

?

These

are

faults

which

caus

e

the

voltage

to

go

outside

normal

limits

for

a

period

of

time.

Transient voltages are characterized by three things:

VeryHigh Voltage, Occur For A Very Short Period of time (in nanoseconds) and High Occurrence.

Many transients cause damage to micro-semiconductor chipsets by degra ding their performance.

This damage is cumulative and eventually reaches apoint where

sudden and complete failure of