The conductivity of these light emitters is determined by both the material itself and the added dopants. As we already know, when a voltage of straight polarity is applied through the p-n junction, a current will begin to flow, and when electrons and holes recombine, energy is released corresponding to the visible range of the spectrum with a wavelength of 700 to 400 nm.
To obtain luminescence in red and yellow regions, semiconductor MDGS (multipass double heterostructures) based on GaAlAs and AlGalnP are used, and for green and blue luminescence - based on indium and gallium nitrides and their derivatives (InN, GaN, InGaN, AlInGaN).
Radiation is generated at the pn junction between the crystal and the crystal holder, to which a voltage of the required polarity is supplied through the electrodes. With the help of a reflector, lateral radiation is directed along the optical axis of the light emitting element. All internal elements are filled with transparent polymer with the highest refractive index, which is the body. The dome of the body acts as a lens.
External pins are used not only for supplying voltage but also for fixing on PCBs. In addition to the end structure, there are elements with external terminals located in the plane of the base.
In the early nineties, the first blue and white LED was introduced to the world. Since then, the technological race in the production of super-bright high-power white LEDs has begun and continues to the present. It is known that no LED is capable of emitting white light, since white light is the sum of all colors. Therefore, the color of the radiation depends on the width of the energy band gap of the transition, where the recombination of electrons and holes takes place.
The energy band gap, as we already know, depends on the material added to the semiconductor. So to obtain white light, a thin layer of phosphor is applied to a blue LED crystal, which emits yellow and red light under the influence of the blue spectrum. As a result of mixing blue, yellow and red, the output is white light.
Superbright LEDs typically run between 2.8 and 3.9 volts. The service life of LEDs, although quite long, is very sensitive to current overloads. To exclude their overload and, therefore, complete or partial failure, it is necessary to use it on specialized microcircuits, and to adjust the brightness of the glow, it is recommended to use pulse modulation. The structure of a typical super-bright LED is shown in the diagram below:
It should be mentioned that a powerful super-bright LED made in violation of the technology loses its light output after some time of operation. As a rule, they are sold at Chinese auctions cheaper than their counterparts. This is due to the fact that the epoxy material of the bulb turns yellow and the emissivity of the blue LED chip with a phosphor layer applied to it decreases.
Basic parameters of LEDs |
LED characteristics can be divided into input and output. TO input parameters include: direct current I pr; forward voltage drop at rated current U pr; maximum allowable reverse voltage U arr. Max; volt-ampere characteristics.
Rated forward current I pr through a crystal with a size of 0.1 x 0.1 mm is equal to 20-40 mA. The maximum permissible forward current Ipr max depends on the cooling conditions, the design of the LED, and in the pulse mode, on the duty cycle of the pulses.
Forward voltage drop U pr on the LED at rated current depends on the energy of the emitted quanta and ranges from 1.5 V for diodes emitting in the infrared region, to 4.2 V for LEDs emitting blue and violet light.
TO output parameters include: luminous flux F; radiation angle; axial luminous intensity I 0; chromaticity of radiation or wavelength in the region of maximum radiation λmax; light output (for IR diodes - efficiency); brightness L(indicated for luminous plates); inertia T; lumen-ampere characteristic (dependence of the luminous or radiant flux of the LED on the direct current).
Handbook for domestic LEDs |
In this guide, you will find parameters and descriptions for the following domestic LEDs KL101A, KL101B, KL101V, 2L101A, 2L101B, AL102A, AL102AM, AL102B, AL102BM, AL102V, AL102VM, AL102G, AL102GM, AL102D, AL102AM, 3101B1 -1, AL307AM..NM, AL310A, AL310B, AL316A, AL316B, ALS331A, 3LS331A, AL341A..I, KL360A, KL360B, 3L360A, 3L360B, KLD901A, KLBDIA-1PD-1 , KIPD02V-1L, KIPD02G-1L, KIPD02D-1Zh, KIPD02E-1Zh, KIPM02A-1K, KIPM03A-1K, KIPM04B-1K and many others
Device and parameters of flashing LEDs |
Flashing LED(MS) is a conventional light-emitting semiconductor, but with a built-in integral pulse generator with a pulse repetition rate of 1.5 - 3 Hz. MC is a complete functional device that performs the function of light signaling.
In addition, the flashing LED is quite versatile - its supply voltage can be in the range from 3 to 14 volts for high-voltage, and from 1.8 to 5 volts for low-voltage MS. The use of flashing LEDs is justified in compact circuits, where there are strict requirements for the dimensions of components and power supply - flashing LEDs are very energy efficient, because the MS circuit is built on MOS structures. Such an LED can easily replace an entire functional unit. In schematic diagrams, it is indicated as follows.
If you look through the transparent body of the MC, you can see that it is structurally composed of two parts. A light-emitting crystal is placed on the base of the negative terminal (cathode). The internal generator chip is located at the base of the anode lead. Three jumpers connect all the components of this device.
The generator chip consists of an RF generator - it works constantly - its frequency fluctuates in a range close to 100 kHz. Together with it, a divider on logic elements works, which divides the RF pulses to a level of 1.5 - 3 Hz.
How to check the LED |
The internal structure of an LED is similar to a conventional diode. Therefore, it can be checked in the same way - by switching in the forward direction, i.e. A positive voltage must be applied between the anode and cathode of the LED. Checking is not a big problem if you have a multimeter. Unlike standard silicon diodes, the forward voltage of which is about 0.6 ... 0.7 V, the LED has a higher value of this parameter, moreover, depending on the color of the glow and the material of manufacture. So red light-emitting semiconductors have a voltage of 1.5 ... 2 V, green - 1.9 ... 4 V, white - in the region of 3 ... 3.5 V.
