LED light-emitting diode common sense
Semiconductor devices, including semiconductor light-emitting diode (referred to as LED), digital control, control symbols, Jack and dot-matrix display tube (the tube matrix). In fact, digital control, symbols tube, pipe and Jack matrix light-emitting tube for each unit is a light-emitting diodes.
First, semiconductor light-emitting diodes working principle, characteristics and application
(A) LED light-emitting principle
LED by Ⅲ - Ⅳ family compounds, such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP (gallium arsenide phosphate), made of semiconductors, which is the core of the PN junction. Therefore, it is generally IN characteristics of the PN junction, which is connecting, closing reverse, the breakdown characteristics. In addition, under certain conditions, it has a light-emitting characteristics. In the forward voltage, by e-N area into the area P, P zone into the hole by the N zone. Into the other side of a small number of regional carrier (minority) part of the carrier and the majority (more), and light-emitting complex, as shown in Figure 1.
Assumptions in the light-emitting P occurred in the district, then injection and electronic valence band hole and luminescent compound directly, or light-emitting center was first arrested after the hole and luminescent compound. In addition to this light-emitting compound, but also by some non-light-emitting Electronic Center (between the central belt, referred to in the vicinity of the middle band) to capture, and then combined with the hole every time, the energy released is not and can not form a visible light. The light-emitting composite volume compared with the non-light-emitting composite volume ratio of greater light, the higher quantum efficiency. Since the compound is the proliferation of minority carrier in the region of the light-emitting, so only light in the PN junction near the surface within a few μm produced.
Theory and Practice shows that the peak of the optical wavelength λ with the region's light-emitting semiconductor materials band gap Eg, that is, λ ≈ 1240/Eg (mm) in the Eg-units for e-volts (eV). Can produce visible light (380nm wavelength in the red light here ~ 780nm), Eg of the semiconductor material should be between 3.26 ~ 1.63eV. Than long-wavelength red light to infrared light. Now infrared, red, yellow, green and blue light-emitting diodes, but the cost of Blu-ray diode, high prices, generally do not use.
(B) LED features
1. Limit the meaning of the parameters
(1) to allow power Pm: to allow both ends of the increase in the LED forward voltage direct current flow and its current value of the product. More than this value, LED fever, damage.
(2) are the largest direct current IFm: to allow the greatest increase in the forward DC current. This value is more than can damage diodes.
(3) reverse the greatest voltage VRm: increase the maximum allowed by the reverse voltage. More than the value of the light-emitting diode breakdown may be damaged.
(4) working environment topm: light-emitting diodes can be a normal working temperature range. Lower or higher than this temperature range, the LED will not work, greatly reducing efficiency.
2. The significance of electrical parameters
(1) and the spectral distribution of peak wavelength: a light-emitting diodes are made not a single wavelength of light, its wavelength by and large shown in Figure 2. Can be seen from the chart, issued by the LED light in a certain wavelength of light λ0 the most, the wavelength of peak wavelength.
(2) luminous intensity IV: light-emitting diode light intensity is usually fingering line (of cylindrical LED refers to its axis) direction of luminous intensity. If in the direction of radiation for (1 / 683) W / sr, while a light-emitting candela (symbol for the cd). As the general LED LED intensity of the small, so often luminous intensity candela (mcd) for the unit.
(3) semi-spectral width Δλ: it said LED spectral purity. Refer to Figure 3 1 / 2 peak intensity corresponding to the wavelength of the two intervals.
(4) semi-value angle θ1 / 2 and perspective: θ1 / 2 refers to the value of luminous intensity for half of the value of the axial strength and direction of the light-emitting axial (normal) angle. 2 and a half times the value of the angle to angle (or half-power angle).
Figure 3 shows the 2 different types of LED luminous intensity distribution angle. In the vertical (normal) AO coordinates for the relative intensity LED (light-emitting strength and that is the largest of the luminous intensity ratio). It is clear that the normal direction on the relative strength of light-emitting 1, leaving the normal direction of the bigger point of view, the smaller the relative luminous intensity. This map can be worth half the value of perspective or angle.
(5) forward operating current If: It is the normal light-emitting diode light-emitting current value at the time of being. In actual use should be required to choose IF in the following 0.6 IFm.
(6) forward voltage VF: parameters are given in the table in the operating voltage is being given under the current. In general IF = 20mA when measured. LED forward voltage VF in the 1.4 ~ 3V. When the temperature outside, VF will decline.
(7) VI characteristics: light-emitting diodes of the relationship between voltage and current that can be used Figure 4.
in the forward voltage is less than a certain value (called threshold), a very small current, non-luminous. When the voltage above a certain value, being current with the rapid increase in voltage, light-emitting. VI curve can be drawn by the LED's forward voltage, reverse current and reverse voltage, and other parameters. LED's are the reverse leakage current IR <10μA below.
(c) LED classification
1. According to the color LED light-emitting points
by LED luminous color, can be divided into red, orange, green (and yellow, and green sub-standard green and pure green), Blu-ray and so on. In addition, some light-emitting diode contained in two or three color chips. According to a LED light-doped Department or mixed scattering agent, colored or colorless, the color of a variety of light-emitting diodes can be divided into colored transparent, colorless and transparent, colored and colorless scattering four types of scattering. -Scattering light-emitting diodes and up to do with light.
2. LED according to the characteristics of the sub-Smooth
by LED features a smooth round at lights, side lights, rectangular, LED face, side-pipe, the installation of the surface with micro-tube, and so on.
round by the diameter of light into φ2mm, φ4.4mm, φ5mm, φ8mm, φ10mm and φ20mm and so on. Foreign usually φ3mm of the light-emitting diodes recorded as T-1; bring φ5mm recorded as the T-1 (3 / 4); to φ4.4mm recorded as the T-1 (1 / 4). By the semi-circle on the estimated value of the angle size of the luminous intensity distribution angle. From the angle luminous intensity distribution to sub -
there are three categories:
(1) the high-point. General pointed to epoxy package, or with metal reflector cavity package does not increase scattering agent. Half-value angle of 5 ° ~ 20 ° or less, the high point, can be used for partial lighting source, or in conjunction with the light detector which is part of auto-detection system.
(2) standard. Normally used for light, the value of the semi-angle 20 ° ~ 45 °.
(3) scattering type. This is the larger perspective of light, semi-value angle of 45 ° ~ 90 ° or more, the scattering of the larger dose.
3. According to the structure of the sub-light-emitting diodes
according to the structure of light-emitting diodes are at all-epoxy, epoxy package base metal, ceramic package and glass epoxy base closures
structure, and other equipment.
4. And the luminous intensity according to the current sub -
according to current and luminous intensity are common at the brightness of the LED (light-emitting intensity <10mcd); ultra-high brightness of the LED (light-emitting intensity> 100mcd); in the luminous intensity between 10 ~ 100mcd called high-brightness light-emitting diodes. General LED current work in more than 10 mA to a few mA, and low current LED current work in the following 2mA (with the general brightness LED).
In addition to the above classification, there are chips according to the classification of material and classified according to function.
(d) LED Application
due to light-emitting diode color, size, shape, strength and light-emitting transparent and so different, so the use of light-emitting diodes should be based on actual need for the right to choose. As the light-emitting diodes with the largest positive current IFm, the maximum reverse voltage VRm restrictions on the use, should ensure that no more than this value. For safety reasons, the actual current IF in the following 0.6IFm; should be possible reverse voltage VR <0. 6VRm. LED are widely used in electronic equipment and electronic devices as a power indicator light, or micro-level direct light source. Infrared LED is often used in televisions, video recorders, such as the remote control in.
(1) the use of high-brightness light-emitting diodes, or ultra-high brightness of the flashlight to produce micro-circuit shown in Figure 5. Chart resistance in the current limiting resistor R, to ensure that its value should be the highest voltage power supply so that the LED current is less than the maximum allowable current IFm.
(2) Figure 6 (a), (b), (c) of DC power, AC power and the power rectifier circuit instructions.
Figure (a) of resistance ≈ (E-VF) / IF;
Figure (b) of R ≈ (1.4Vi-VF) / IF;
map (c) of R ≈ Vi / IF-in, Vi - AC RMS voltage.
(3) single-level direct LED circuit. In the amplifier or oscillator circuit of the digital pulse output can be used LED output signals that are in working order, as shown in Figure 7. R for the current limiting resistor. Only when the output voltage of the LED is greater than the threshold voltage, LED light-emitting can be.
(4) single-LED can be useful for low-voltage regulators. As the LED is connecting, with the current voltage change very quickly, with the general characteristics of voltage regulator tube regulator. LED voltage stability in the 1.4 ~ 3V, the choice should be based on the need for VF, as shown in Figure 8.
(5) meter. At present, the use of audio equipment in a large number of LED level meter. It is more than the use of LED output signals indicative of the level, that is, the number of light-emitting LED's, said output level. Figure 9 by 5 LED level meter posed. When the input signal level is low, and do not have light-emitting. Input signal level increases, the first-LED1, and then increase the light LED2 ... ....
(e) light-emitting diode test
1. General LED Detection
(1) using multimeter testing.
× 10kΩ with the use of the block pointer multimeter can be more or less determine the quality of light-emitting diodes. Normal, the diode forward resistance for dozens of resistance to 200kΩ, the reverse of resistance value of α. If the resistance are for the value of 0 or ∞, the reverse resistance value is 0 or small, fragile. This method of detection, the field can not see the LED light, can not be blocked because × 10kΩ to provide a larger LED forward current.
If there are two pointer multimeter (with the best models) can be used to check the LED light-emitting situation. With a wire to a multimeter in which the "+" and post another piece of the table "-" post connection. The remaining "-" LED pen then measured the positive (P Zone), the rest of the "+" LED pen then measured the negative electrode (N). Multimeter two are home × 10Ω block.
Under normal circumstances, will be able to get through after the normal light-emitting. If the light is low, not even light-emitting, two multimeter will have to set aside × 1Ω if, if still dark, not even luminous, light-emitting diode on the performance of non-performing or damage. It should be noted, can not be measured beginning at two multimeter × 1Ω, in order to avoid too much current, damage to the light-emitting diodes.
(2) external power measurement.
Regulators or 3V with the source of two series of dry batteries and multimeter (Analog or digital can) can be a more accurate measurement of light emitting diodes, electrical characteristics. To this end as shown in Figure 10 can be connected to the circuit. If measured in VF between 1.4 ~ 3V, and the normal brightness light-emitting can testify to the normal light-emitting. If measured VF = 0 or a VF ≈ 3V, and do not luminous, light-emitting tube that has been bad.
2. Infrared detection of light-emitting diodes
due to the infrared light-emitting diodes, which launched the 1 ~ 3μm infrared light, people can not see. Usually only a single infrared light-emitting diodes transmit power only a few mW, different models of the infrared LED luminous intensity distribution is not the same angle. Infrared LED forward voltage drop is generally 1.3 ~ 2.5V. It is due to launch its human eye can not see infrared light, the LED's use of visible light of the above test can only determine the PN junction is, the reverse is the normal electrical properties, and could not determine whether its light-emitting normal circumstances. To this end, the best preparation for a photosensitive device (such as 2CR, 2DR silicon-based PV) for the receiver. Multimeter with metering at both ends of the battery voltage changes. To determine the appropriate infrared LED forward current of whether infrared light. Measurement of the 11 circuit shown in Figure.
Second, LED light-emitting diodes and the use of file
LED applications in the field, will always be the parallel use of several LED at the same time, due to its LED voltage, wavelength, the brightness of different stars, many diodes in parallel with the use of color would be inconsistent brightness of light and shade, and so different, Therefore, when considering the use of the following principles in order to avoid the use of the result is not satisfactory:
In the same product, as far as possible, using the same grade of the product, if it can not meet to consider a few of the following
The same product, to maintain the LED voltage (Vf) of the same premise, consider the same wavelength, the brightness of adjacent stalls products, such as the blue # 343, # 443 and # 543 and # 533 and # 433, with 443 # The lack of time, and # 543 or # 343.
As the customer's product quality, in principle, the same products, as far as possible not to cross-file; such as # 343 and # 543 as far as possible not to use the same products.
If Article 2 is still unable to meet under the premise, the LED voltage to consider the same wavelength adjacent, adjacent brightness / 2 of the first instance with identical.
Only series line is to focus on the same wavelength, the voltage on the order in which they agreed to consider.
There are various products in order, focus on different products were the same wavelength, the same brightness arranged in chronological order.
Our products are shipped when they are used by automatic machines to spectrophotometry, color, voltage points, the same packaging bags are generally the same level of product.
LED just above and to recommend ways of using the file, in the actual production, the user can own products based on the characteristics of the corresponding adjustment or other methods used.
Third, the application of common sense
LED welding conditions
(1) soldering iron: iron (up to 30W) of-the-art temperature does not exceed 300 ℃; welding time is not more than 3 seconds; welding position at least 2 millimeters away from the gel.
(2) Wave: welding Baptist maximum temperature 260 ℃; Baptist welding time is not more than 5 seconds; Baptist welding position at least 2 millimeters away from the gel.
Pin-forming methods
(1) required from the 2 mm gel scaffold can be bent.
(2) must stenting or fixture to be completed by professionals.
(3) stent must be completed before welding.
(4) stenting need to ensure the pin and line spacing and the same board.
Fourth, cleaning
When cleaning chemicals colloidal must be extra careful because some of the chemicals on the surface of colloidal have caused injury and fading as TCE, acetone and so on. Ethanol can be used to clean, impregnation, the time at room temperature not more than 3 minutes.
Fifth, electrostatic protection
Static and the current sharp increase will generate LED damage, InGaN products use the use of anti-static devices, such as gloves and protective belt.
Note: when using the Human Body Model HBM <1000V; discharge machine mode <100V.
