LED light based on knowledge (a)
Semiconductor devices including light emitting diodes (referred to as LED), digital control, sign control, rice and dot matrix character display tube (referred to as the matrix of tubes) and so on. In fact, digital control, sign control, meter tubes and matrix character of each tube is a light-emitting diode light-emitting unit.
First, the working principle of semiconductor light-emitting diode, characteristics and applications
(A) LED light principle
Light-emitting diodes by Ⅲ - Ⅳ compound, such as GaAs (gallium arsenide), GaP (gallium phosphide), GaAsP (gallium arsenide phosphorus) and other semiconductor processing, and its core is PN junction. Therefore, it has the general characteristics of PN junction of the IN, ie the forward and reverse cut-off, breakdown characteristics. In addition, under certain conditions, it also has light-emitting properties. In the forward voltage, electron injection from the P N Zone area, hole injection from the P area N area. Into other areas of the minority carriers (minority carriers) part of the carrier with the majority (more children) composite and light,
Suppose P area in the light occurs, then the injected electrons and valence band holes recombine directly to light, or luminescence center was first captured, and then with the hole recombination. In addition to this light-emitting compound, but also some of the electrons are non-luminescent center (the center between the conduction band, medium band near the middle) to capture, and then with the hole recombination, the energy released each time is not, can not form a visible light. The amount of light relative to the composite light-emitting compound of the proportion of non-larger, higher quantum efficiency. Since minority carrier diffusion zone compound is light, so light only in the * near PN junction surface produced within a few μm.
Theory and Practice shows that the peak wavelength λ of light emitting regions of semiconductor material and relevant, that is,
λ ≈ 1240/Eg (mm)
Eg where the unit of electron volts (eV). If we can produce visible light (wavelength of 380nm ~ 780nm violet red), Eg of semiconductor materials should be between 3.26 ~ 1.63eV. Longer wavelength than the red light to infrared light. Now have infrared, red, yellow, green and blue LEDs, but the cost of Blu-ray diode, the price is high, use of non-universal.
(B) LED lights feature
1. Significance of the limit parameters
(1) to allow power Pm: Can we add in the LED forward DC voltage across it with the current flowing through the product of the maximum. Than this value, LED fever, damage.
(2) Maximum forward DC current IFm: Can we add the largest positive DC current. Than this value can damage the diode.
(3) The maximum reverse voltage VRm: increase the maximum allowed reverse voltage. Than this value, breakdown of light-emitting diodes may be damaged.
(4) work environment topm: light-emitting diode can be a working temperature range. Below or above this temperature range, the LEDs will not work, efficiency is greatly reduced.
2. The significance of electrical parameters
(1) The spectral distribution and peak wavelength: one light emitting diode is not issued by a single wavelength. Issued by the LED light in a wavelength of maximum intensity λ0, the wavelength of the peak wavelength.
(2) The luminous intensity IV: LED luminous intensity usually is defined as the line (on the LED is its cylindrical axis) direction of the light intensity. If the radiation intensity in that direction is (1 / 683) W / sr, then the light-emitting 1 candela (symbol for the cd). Due to the general LED of the LED intensity, so the common candela luminous intensity (mcd) for the unit.
(3) spectral half width : it represents the purity of the LED spectrum. Is shown in Figure 3 1 / 2 peak intensity corresponding to the interval between the two wavelengths.
(4) half-value angle θ1 / 2 and angle: θ1 / 2 is the intensity value of luminous intensity is half the axial direction and light axial (normal) angle.
2 times the half-value angle of the perspective (or half-power angle). Given two different types of light-emitting diode light intensity angular distribution. In the vertical (normal) AO of the coordinates of relative intensity (ie light intensity and the ratio of the maximum luminous intensity.) Clearly, the normal direction of the relative intensity of 1, leaving the greater the angle of normal direction, the smaller the relative intensity. This figure could be half-value angle or angle value.
(5) Forward Current If: It refers to the normal light-emitting diode forward current time value. In actual use should be selected by IF in 0.6? IFm below.
(6) forward voltage VF: parameters of the work given in the table at a given voltage is obtained under forward current. Generally in the IF = 20mA when measured. LED forward voltage VF in the 1.4 ~ 3V. When the outside temperature, VF will decline.
(7) VI characteristics: light emitting diode between the voltage and current can be expressed in Figure 4.
In the forward voltage is less than a certain value (called threshold), the current is very small, not light. When the voltage exceeds a certain value, the rapid increase in forward current with voltage, luminous. VI curve can be drawn by the LED's forward voltage, reverse current and reverse voltage and other parameters. Positive reverse leakage current IR LED (Editor：admin) |