Emitting diode and fotoforates

pp 166-178

will provide some basic
elements of optoelectronics,
that is the science that studies the provisions
and operate the combined
optical devices and functions. At the end of
chapter, the student must:
• Does understanding the mechanisms of the emitting and
the photoelectric effect.
• Knows the construction of light-emitting diode (LED).
• understands the use fotoforaton like
photoresistance the LED (making), the phototransistor
and other fotodiataxeis

K E F A L A I O

INFORMATION OPTIKOHLEKTPONIKHS

6.1 Fotopiges
6.1.1 photoemission
    It can give a definition of light as follows:
    Light is the kind of energy, which stimulates the eye of man as a result of looking at various objects.
    As is known from physics, light is visible electromagnetic radiation (according to the theory of Maxwell) whose spectrum occupies an area between the visible infrared and ultraviolet radiation. The frequencies and wavelengths are given in the following table:
Radiation
Frequency (f)
Wavelength (l)
Infrared
1011 - 3,85 THz
0,1 cm - 790 nm
Visible
385 - 789 THz
790 - 390 nm
Ultraviolet
789 THz - 1017 THz
390 - 0,5 nm (5 D)

1THz = 1012 Hz
1A (Angstrom) = 10-10m
Table 6.1.1.
    Between the frequency (f) and wavelength (l) of electromagnetic radiation is the relationship?

where c = speed of light = 3 x 108 m / sec
    In each wavelength of the visible spectrum, corresponding to a "color". These colors are the main form the familiar colors of the "rainbow", which are given in the figure below (units in A wavelength, frequency in Hz):

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INFORMATION OilTIKOHAEKTPONIKHI

microwave
Figure 6.1.1 The main colors
The human eye is not equally sensitive by all the colors. The greatest sensitivity is 0.55 wavelength = 550nm non-owned area of yellow color and smaller in the violet and red.
In image transmission sites used 3 colors corresponding to red (R), green (G) and blue (B) which are created and the other 4:
red tricolor

red blue, blue j
tricolored
green
Figure 6.1.2 Prosthetic method of color reproduction
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   Today's technology with the methods of mixing colors, has created thousands or millions of colors.
   Because the expression of the optical radiation frequency is given by very large numbers, as shown above, the expression commonly used in wavelength.
   The radiation, either UV or visible, infrared, or composed of photons, namely infinitesimally "packets" of light energy (also called light quanta), which have double named form, ie particles and materials but have a wave behavior. Photons have energy:
Since = h · f 6.1.2
where h = 6,62 x 10 34 J sec constant called Plank, f = frequency of light in Hz.

      light emission or photoemission is from the material bodies
under conditions such as:
   A) Because of the high temperature which are like the sun
(6000 ° C), the solar arc (3000 ° C), fiery bodies such as incandescent lamps (»2000 -2500 ° C), etc. The light sources are light sources are hot.
   B) Because of lightning developed within
gases or vapors. The light sources are also called cold light sources. The energy required for photoemission taken by electric fields. Such sources are pipes advertising noble gas (neon, krypton, etc.) or mercury vapor lamps (Hg), sodium (Na) hydrogen (H2) KL Fr
   C) Because fluorescence, phosphorescence, chemical reactions and other phenomena. The light sources are cold and the luminescence is due to absorption of incident photons or electrons more energy. The secondary fluorescence radiation lasts as long as the primary and the fluorescence energy is given later for a long time.
   Luminescent properties have some species of the animal kingdom
such as fireflies, some species of fish, plankton, etc.
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INFORMATION OPTIKOILEKTRONIKIS

   Example 6.1.1
    What is the frequency and energy photon has a wavelength lambda = 100 A are given 1 A = 0,1 nm = 10-10 m
Speed of light = c = 3 x 108 m / sec
1 eV = 1,6 x 10-19 Joule.
    Solution
    The frequency of the photon is given by the relation (6.1.2):

This frequency belongs to ultraviolet radiation.
The energy of the photon is given by the relation (6.2) and are:

   Example 6.1.2
    What is the wavelength of the photon, the energy is
Since = 4,13 eV;
    Solution
    The relation (6.1.2) is written:
E = h · f ^ f = long = 4,13 eV 4,13 x 1.6 x 10-19J = 1015Hz
F h 6,62 x 10-34 J sec 6,62 x 10-34 J sec
    This frequency belongs to ultraviolet radiation.
Since = hf = 6,62 x 10-34 J sec x 3 x 10 Hz = 19,86 x 10 - '8 Joule
F

6.1.2. Light emitting diodes, Lenta (LED)
    When a diode polarized correctly, then released energy.
Near "Stripping" is logged and holes
electrons and therefore energy is released. Rectifier diodes in the energy released as heat while emitting diodes LED (Light Emitting Diodes) energy emitted in the form of light. This is due to the material.

Figure 6.1.3 LED. (A) Symbol (b) Construction
   The color of the emitted light radiation can be red, orange, yellow, green, blue. The LED can emit in the infrared. The region of the spectrum emitted by the LED depends on the material of the type and concentration of dopants. The intensity of light emitted is proportional to the forward current of the diode (IF). The types of semiconductors used for LED diodes are GaAsP (Gallium phosphide-male, red or orange), GaP (Gallium phosphide-, orange or green), GaAs (Gallium Arsenide-, infrared), GaAlAs (gallium arsenide-aluminum, bright red), recently SiC (silicon carbide, blue), the recently GaN (Gallium-Nitrogen, blue).
   Figure 6.1.3 shows the symbol of light emitting diode LED arrows show where the light emission.
Manufacturers of LED <Led give some <all of the following: A. Material B. Light color wavelength (l) D. Half angle of the beam (i)
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INFORMATION OPTIKOILEKTRONIKIS

     E. good polarization voltage (VF) to correct the current IF correct maximum IFMAX. F. Maximum sound power IFmax G. Bright relative light intensity H. Maximum power PMAX. The following table gives several types of diodes and LED characteristics as provided by the manufacturers (Siemens, Toshiba, Helwett Packard, Philips, Motorola, Telefunken, etc.)
Type
Material
Color
Length
Half
Good
Light

Wave
Angle
Trend
Intensity

Table 6.1.2. IEO Charaktirtikes toll rates.
   As seen from the table above the normal operating voltage of a diode LED is on average VF »2 V. The price increases when we move from the infrared (1,5 V) to blue (3,7 V) and the normal operating current for several good light emission intensity is between 10 and 20 mA. The maximum operating current for most diodes LED, is IFMAX »50 mA. Therefore the maximum power is PMAX »100 mW. All these must be taken into account when designing LED circuit to prevent damage.
   There are several methods of protection when the LEDs are connected to an electronic circuit. One method consists of series connection of a resistance R of appropriate value, so that it passes from the LED current below the maximum (Figure 6.1.4 than 6.1.3):
Figure 6.1.4 LED Circuit Wiring

6.1.3
   To connect two LED diodes in parallel will have the following circuit:
Figure 6.1.5 Connection 2 LED in parallel

6.1.4
INFORMATION OnTIKOHAEKTPONIKHS

   When the input voltage source is alternating current light-emitting diode protected connecting in series a diode PN and resistance R as shown in Figure 6.1.6
, Vgc - (VF1 + VF2)
IF = R 6.1.5

Figure 6.1.6 Connection iEO AC voltage source with
Vgc
   Example 6.1.3
   In the circuit of the circuit is 6.1.4: Vi = 14 V, R = 600 ohms to find the current flowing through the diode when the voltage is correct wearing VF = 2 V.
   Solution
   The forward current of the diode is:
I = V-VF = 14V-2V = 12V = 20mA = R = 600O 600O = mA =
   Example 6.1.4
   If in the example above the minimum price of a rectal power diode LED, for light is IFmin = 5 mA and the maximum not to be destroyed IFmax = 50 mA, To determine the limits of variation of resistance R for safe operation.
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    Solution
From the relation (6.1.3) we have for the resistance R:

    So the minimum resistance value is?
R _ V: - VF _ 14V - 2V _ 12V _? 400
Rmln IFmax 50 mA 50 mA
    From the same equation, the maximum resistance will be:
Rmax_V ^ _ ^-2V_7 ^ _2400Q
max IFmln 5 mA 5 mA
    So the resistance R varies in the following limits: 240 O <R <2400 O
    The diode LED used on many electronic devices as indicator function or damage. A green LED usually indicates proper operation of the device, while a red usually indicates injury or simply operate the device. The infrared LED are often used to control electronic devices remotely like the TV remote, video or sound system. A two-color LED shows usually every color of the different situations of a control device such as smaller or larger current or voltage, etc.
    The light-emitting diodes used in cases of low voltage and power and have the advantage over incandescent lamps that during normal operation is too large (10,000 to 100,000 hours). Eg with power 2 - 10 mA and voltage of 1,5 - 2,5 V, ie force when P _ 3 -25 mW is almost the same light that would glow with a light force
P _ 6 V x 150 mA _ 900 mW
    A useful application of LED is to show the decimal numbers 0 -9 on a small screen or ntisplei (display) that consists of 7 sections illuminated with LED (7 segment display) as shown in Figure 6.1.7.
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INFORMATION OPTIKOILEKTRONIKIS

Figure 6.1.7 viewer seven parts
   The 7 LED common anode and have separate cathodes 7 (a, b / c / d / e / f / g). The common anode connected to the positive terminal of power source, typically +5 V, while the cathodes are connected via resistors 7 and 7 switches the earth. In this case the viewer is called common anode. If the cathode is common and the anodes are connected via resistors 7 and 7 switches to +5 V, the viewer is called common descent. The resistors used to protect the diodes from large currents are usually limited to 20 -25 mA. The resistance value depends on supply voltage and current to be passed through the diode-toekpompis imitation. It should be noted that in addition to seven LED is usually for one more decimal integers separated by decimal points.
   Inducing currents in two passages through 7 will be pointing out the relevant parts to get the numbers 0-9. So if you pass current from the photodiodes a, b, g, e, d to obtain the number 2, appearing in the form:

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   They can also be viewed appropriate combinations of letters and lowercase Latin letters like A, B, C, D, E, F, B, C etc.
     The illustration of decimal numbers used for indications of electrical quantities in digital measuring instruments such as ammeter, voltmeter, frequency meter etc.
   If you combine 2, 3 or 4 parts 7-imagers is possible to measure electrical quantities expressed with 2 or 3 or 4 digits (digits). More information about the 7-segment indicator will be provided in the course of the Second Class "Digital Electronics".
   Example 6.1.5
   Designed to 7-segment indicator circuit which will reflect the number 6. The mains voltage is 5 V and maximum current of the LED is IFmax _ 25 mA.
   Solution
   In order to have the number 6 should be illuminated parts
a, f, g, c, d, e, ie they should close the circuit through respective LED switches and resistors as shown in
Figure 6.1.7 The protection resistor values will be calculated based on the value of supply voltage and maximum current:

Common anode

Figure 6.1.8 Illustration of the decimal number 6

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INFORMATION OPTIKOILEKTRONIKIS

   The following table illustrate the indicators are 7 parts to their characteristics.
Type
Color
Good Trend
VF (V)
Maximum reversible. Voltage VR, (V)
Luminous Intensity mcd / mA
Milos wave l (nm)
TLR312
Red
2 V / 15mA

TDS515
Green
2,4 / 20mA

2,8-5,6 / 10mA
565
HDSP3903
Bright Red
2,6-3,5 / 100mA

Table 6.1.3 Indicators 7 segments
6.2 The photoelectric effect
   In Chapters 2 and 3 indicated that the removal of electrons from metal or semiconductor is needed to provide enough energy to free electrons are outside the material. This action may be of different forms such as: A. Electricity B. C. Thermal energy Electromagnetic energy D. Chemical energy.
   This section refers to the change in conductivity of the materials when light is incident on the surface thereof. This action is due to the photoelectric effect.
   For visible light photons have energy 1,6 eV - 3,3 eV and much larger in the ultraviolet. The energy required to remove an electron from the covalent bonds that hold the atoms of the pure semiconductor is 0,72 eV for germanium (Ge) and 1,12 eV for silicon (Si).
   Therefore the energy photons are in the visible and ultraviolet light and infrared part of it is enough to dislodge electrons from the valence bond. Thus, the incidence of photons, electrons of the semiconductor valence absorb energy and jump from the valence band to the conduction band, overcoming the restricted zone. This results in the creation of free electrons and holes that contribute to the conductivity. This results in increasing the density of free institutions and thus increase the conductivity of semiconductors, namely the decrease of the resistivity of these.
   This transfer of electrons, the absorption of photons, shown in Figure 6.2.1
Photon
 Zone agogimoitas

 Apagopefmevi zone

Valence band
Figure 6.2.1 The photoelectric effect
   The above fact, due to increased conductivity allows us to construct specific provisions of which the conductivity increases or decreases depending on the intensity of incident light to the surface and are called generally fotodiataxeis.

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