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6.3 Fotoforates, Fotodiataxeis
The fotoforates used too much in opto-ing applications such as for detecting codes, products (bar codes), the image scanners (scanners), to detect flame (fire detection), alarms in adaptive (interfaces) devices, remotely control (telecontrol) TV, video, audio
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systems, etc. The fotodiataxeis distinguished fotokypseles. photodiodes, phototransistor, photoresistance, optocouplers (optocouplers), optical switch, etc.
The fotodiataxeis constructed with plastic or metal housing. On one side there is a "window" glass or plastic, to enter the light. In the following paragraphs will examine a few fotodiataxeis.
6.3.1 photoresistance
The photoresistance resistances which are made of special semiconductors such as selenium (Se), cadmium sulphide (CdS), lead compounds and sulfur etc. In photoresistance reduce the resistance when the surface of light strike an appropriate wavelength.
The photoresistance called LDR (Light Dependent Resistors)
The initial resistance is quite large (MO) and decreases in the intensity of light impinging on the surface, as shown in Figure 6.3.1.
° (Lux)
Figure 6.3.1 Variation of resistance with the radiant intensity
The symbol of photoresistance are:
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Figure 6.3.2 photoresistance
The main features of photoresistance are:
A. The resistance value when not illuminated (dark value).
B. The limits of change resistance when illuminated.
C. The time required to obtain the final resistance value.
D. The maximum voltage applied to photoresistance.
E. Capacity of H.
A common photoresistance trade is the company's RCA 4442 and is mainly used for switches On ff.
6.3.2. Liquid
The LEDs are PN contacts to which reverse polarity. Under reverse bias is a very small current flowing through the diode, see chapter 3, and the case is called dark current (dark current), ID. When light strike created entities (holes and electrons) in the stripping area and reverse current increases. The extra power is required under current lighting (light current) or photocurrent (Photocurrent) and is denoted by IP or Ile
The photocurrent is proportional to the intensity of incident light.
The characteristics of photodiodes identified by their manufacturers are:
A. Angle of light beam.
B. dark current (ID)
C. Maximum wavelength ^ max)
D.Efaisthisia current (mA / Lux and Ma / or impetigo A / W) or photocurrent (Ip,
Ile)
E. Capacity (C)
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F. Maximum reverse voltage (VRmax)
Maximum sensitivity are LEDs in the near infrared light (850nm-950nm).
Table 6.3.1 given the characteristics of some fotodio-don trade.
Type
Half Angle
the
NA dark current
Sensitive. Power Ma
Maximum Wavelength
Maximum reversible. trend
Capacity PF
Table 6.3.1. Features LEDs
Below is the symbol of the photodiode and the connection of the DC circuit. At the same circuit LED photo shows where you can see the "window" in front of.
(A) (b) (c)
Figure 6.3.3 (a) symbol, (b) Connect a circuit, (c) Image
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The following figure is the typical voltage-current curve of the photodiode BPW20, for different values radiant.
Reverse voltage VR (V)
Figure 6.3.4 Curves voltage - current in reverse polarity, the LED
BPW20
6.3.3 phototransistor
The phototransistor is similar in construction and operation of the transistor contact. It has a "window" that allows the system can illuminate the base-collector contact. The collector photocurrent of the diode and thus enhanced the phototransistor is 100-500 times greater photosensitivity of the photodiode and substantially corresponds to a photodiode and a current amplifier.
For these reasons, the phototransistor can be operated with or without the polarization basis. Figure 6.3.5 and are given two ways to connect a phototransistor circuit and symbol.
Figure 6.3.5 phototransistor in a common emitter connection symbol (s), (b) polarization in the base, (c) Without polarization
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INFORMATION OnTIKOHAEKTPONIKHS
No lighting is a small leakage current from the collector to the emitter (Icbo). The collector current is given in equation 6.3.1, when there is polarization in the base and the equation 6.3.2, when it exists.
6.3.1
6.3.2
The lcbo is the reverse current collector base, and b is the base-strengthening current collector.
In this light, the reverse current increases due lcbo the photo-diode current of the collector. Suppose that this increase in power is lP. Then the collector current will be:
Icp = (b +1) ('cbo + Ip) 6.3.4
for the case without polarization of the base is the most common and economical.
Different types of phototransistor is sensitive to other visible light, infrared and other others in the ultraviolet and X-rays
The following table gives certain types of phototransistor with their characteristics.
Type
Current darkness
Open Base
Table 6.3.2 phototransistor
The characteristic curves of the phototransistor resemble the curves of the transistor contact and give the photocurrent, Ip, versus the collector-emitter voltage parameter with the lighting Lux.
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6.4 Other Fotodiataxeis
There are other fotodiataxeis than those reported used either as sensors or control remotely, <in
electrical isolation circuits where there is but visual connection.
Such optoelectronic devices or fotodiataxeis are imitation-tothyristor, fotoaivo, fotoiiivo, the diode Laser, the fotokypseli, the optical sensor, optical switch and finally the optocoupler (- optocoupler).
O optocoupler or optokapler (optocoupler) is marketed in a form similar to that of integrated circuits, ie 6 or 8 pins (pins), and consists of an infrared LED and a phototransistor. The phototransistor can be applied to the base terminal bias or may not have.
Such optocoupler marketed by various companies such as CNY13, 4N25 -28, 6N135-136, etc. Figure 6.4.1 shows the 4N25 to the terminals and the fotodiataxeis.
Figure 6.4.1 yptikosyzefktis 4N 25 (a) Internal circuit, (b) Image
By using an optocoupler circuit to electrically isolate the entrance and exit of the circuit and a single optical link. Its operation is as follows:
The light emitting diode (LED) polarized correctly (terminals 1.2) and direct current through the IF becomes infrared radiation from the LED emitted and received by the phototransistor (pins 4,5,6). This radiation is converted into electricity and leaves the collector as an IC (pin 5).
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This current esodou is enhanced relative to the input current and the ratio Ic / IF (also called current-ratio, CTR) can reach values up to 1000.
Optocouplers, which are widely used in modern microelectronics, will be described and analyzed more in Second and Third Class.
ABSTRACT 6
• The light emission or photoemission is done under special conditions such as high temperature, lightning, fluorescence, phosphorescence, chemical reactions, etc.
• photoelectric effect is the phenomenon in which electrons are emitted from the surface or a material change in the conductivity when the surface of light strike, with appropriate photon energy.
• The absorbed photon gives energy to the electrons of a semiconductor switch to the valence band to the conduction band. This creates free electrons and holes, thus increasing the electrical conductivity.
• The light-emitting diode (LED) is a special diode made by specialists such as semiconductors GaAsP, GaP, GaAs, Sic and emits light energy (visible, infrared) in the leakage current of proper polarity.
• The intensity of light emitted by an LED is proportional to the current flowing through the usual and proper voltage required is approximately 2V.
• The diode LED used to display numbers in special circuits called 7-segment indicators are composed of 7 LED with common anode or cathode.
• The photoresistance fotoforatis is one whose value is reduced when the surface of light strike.
• The LED is a diode which is inversely polarized and
passed over by an electric current when light shines on the surface.
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KOS 5.2, R2 = 10,4 KO.
Calculate the total current of the circuit and the currents of the LED.
6.1. If the LED diode's voltage drop shape is 2,5 V, to find the current that flows through the
(R = 950 Ohms).
6.2. When an LED emits at a wavelength of lambda = 5650 A, what is the bright light?
A. Visible
B. Infrared
C. Ultraviolet.
6.3. Be found in Table
6.1.2 The types and characteristics of the red LED.
6.4. From Table 6.3.1 To determine the characteristics of
LED Capacity with less.
• The phototransistor is similar to the transistor contact. When the illuminated surface of the display panel of the enhanced photocurrent generated. The photocurrent is proportional to light intensity.
• In a phototransistor, it is necessary to polarize the base.
• O combination of a light emitting diode (LED) and a phototransistor is a very useful fotodiataxi called optikosyzefktis (optocoupler). O optocoupler is used to electrically isolate the entrance and exit of two circuits.
QUESTIONS - Exercises
6
6.5. Report emitting methods.
6.6. What is photoelectric effect?
6.7. How much energy it contains a photon?
6.8. LED diodes that emit light?
6.9. Draw circuit with indicator (display) 7 parts, which reflect the number 9.
6.10. What is the difference between an LED diode contact PN;
6.11. Given the following circuit consisting of two light-emitting diodes (LED) and is: V = 12 V, Vf1 = VF2 = 1,6 V, R =
