1. Main features of light-emitting diode LED
(1) Working under the conditions of low voltage (1.5~2.5V) and small current (5~30mA), sufficient brightness can be obtained. (2) The luminous response speed is fast (10-7~10-9 s), the high frequency characteristic is good, and the pulse information can be displayed.
(3) Good monochromaticity, common colors are red, green, yellow, orange, etc.
(4) Small size. The shape of the light-emitting surface is divided into circle, rectangle, and special shape (triangle, etc.). Among them, the outer diameter of the round tube has specifications such as p1, (p2, (p3, (p4, p5, p8, p10, p12, p15, p20 (mm), etc.), and the diameter of 1mm belongs to the ultra-micro LED.
(5) Good anti-vibration and impact resistance, low power consumption and long life. Since the PN junction of the LED works in a forward conduction state, the power consumption of the original radio is low. As long as the necessary current limiting measures are added, it can be used for a long time.
(6) Flexible use, it can be made into digital tube, character tube, level display, dot matrix display, solid light-emitting board, LED flat-pole TV screen, etc. according to needs. (7)) Easy to match with digital integrated circuits.
2. The principle of light-emitting diodes
Inside the light-emitting diode is a PN junction with light-emitting characteristics. When the PN junction is turned on, it relies on the injection of minority carriers and subsequent recombination to emit light. The appearance, symbol and volt-ampere characteristics of ordinary light-emitting diodes are shown in Figure 1. The forward volt-ampere characteristic curve of the LED is relatively steep, and there is almost current before the forward conduction. When the voltage exceeds the turn-on voltage, the current rises sharply. Therefore, LED is a current-controlled semiconductor device, and its luminous brightness L (in cd/m2, read as candela per square meter) is approximately a positive double with the forward current IF, and there is a formula
L=K IFm
In the formula, K is the proportional coefficient, in the small current range (IF=1~10mA), m=1.3~1.5. When IF>10mA, m=1, formula (5.10.1) is simplified to L=KIF
That is, the brightness is proportional to the forward current. Taking phosphorous arsenic wiping yellow LED as an example, the relationship between relative luminous intensity and forward current is shown in Figure 2. The forward voltage of the LED is related to the forward current and the semiconductor material of the die. When using, you should select the appropriate IF value according to the required display brightness (usually about 10mA, for high-brightness LEDs, you can choose 1~2mA), to ensure that the brightness is moderate, and the LED will not be damaged. If the current is too large, the PN junction of the LED will be burned. In addition, the life span of the LED will be shortened.
