The Principle of Light-emitting Diode SMD LED and Through-hole LED

Light emitting diode is a kind of semiconductor diode, which can convert electric energy into light energy. Light emitting diode is composed of a PN junction like ordinary diode, and also has single guiding electricity. When the positive voltage is applied to the light emitting diode, the holes injected from the P-region to the N-region and the electrons injected from the N-region to the P-region are compounded with the holes in the N-region and the P-region respectively within a few microns near the PN junction. Fluorescence that produces spontaneous emission. In different semiconductor materials, the energy states of electrons and holes are different. When electrons and holes are combined, the amount of energy released is different. The more energy released, the shorter the wavelength of light emitted. Commonly used are red light, green light or yellow light emitting diodes. The reverse breakdown voltage of light emitting diodes is greater than 5V. Its forward volt ampere characteristic curve is very steep, so it must be connected in series when used. A current limiting resistor controls the current through the diode.

The current limiting resistance R for LED working can be calculated by the following formula:
R = (E - UF) / if
(Note: e is the supply voltage; UF is the forward voltage drop of LED; if is the normal working current of LED)
The core of LED is composed of p-type semiconductor and n-type semiconductor. There is a transition layer between p-type semiconductor and n-type semiconductor, which is called PN junction. In the PN junction of some semiconductor materials, when a small number of injected carriers are combined with a large number of carriers, the excess energy will be released in the form of light, so that the electrical energy can be directly converted into optical energy. A few carriers are difficult to inject, so they don't emit light. This kind of diode made by the principle of injection electroluminescence is called light-emitting diode, or led in general. When it is in a positive working state (i.e. the positive voltage is applied at both ends), when the current flows from the LED anode to the cathode, the semiconductor crystal emits light of different colors from ultraviolet to infrared, and the intensity of light is related to the current.
The function of LED
Light emitting diode (LED) is a kind of light-emitting display device which is made of gallium phosphide (GAP) and other semiconductor materials and can directly convert electric energy into light energy. When there is a certain current passing through it, it will light up. Figure 1 LED circuit graphic symbol.