Design of automotive lithium 18650 li ion battery and driver circuits

　　LED is a new type of semiconductor light source that is efficient and environmentally friendly. It has advantages that other light sources cannot match. It has a bright future in automotive lighting applications. LEDs can be combined into LED arrays in different ways such as series and parallel to meet the requirements of automotive lighting intensity. In view of the light-emitting characteristics of LED, the design and characteristics of the LED driver are focused on, and the current problems and solutions of LED are briefly described.

　　1 Functions and requirements of automobile lights

　　At present, cars are becoming increasingly common and have become the main means of transportation. Driving safety has aroused widespread concern in society. According to incomplete statistics, the mileage traveled by cars at night or with insufficient natural light accounts for 25% of the total mileage, and the traffic accidents that occur here account for 40% of the total accidents, and more than half of the casualties occur at night. . Therefore, exterior lighting and signal lights are key components for safe driving and must meet the following conditions:

　　(1) There is no delay in lighting up the car lights, and the response time is faster, giving the driver more reaction time.

　　(2) The lighting brightness is strong, which improves the driver's field of vision at night or when there is insufficient natural light, and at the same time makes the indicator light outside the vehicle stronger.

　　(3) High earthquake resistance and high working reliability to avoid accidents caused by lighting failures.

　　(4) Energy saving, which can effectively reduce exhaust gas emissions and protect the environment.

　　(5) Due to the increasingly fierce competition in automobile sales, the design of car lights must be practical and beautiful.

　　2LED becomes the new star in automotive lighting material selection

　　2.1 Working principle of LED

　　LED is a special diode, a semiconductor device that forms a PN junction through doping and other means. When the diode conduction conditions are met, current flows through the LED, releasing energy in the form of light and heat. LED is a current-controlled current-type component. Its luminous intensity mainly depends on the passing current. When it is forward-conducting, its voltage drop is very high, and it has a certain fluctuation range.

　　Since LEDs do not emit infrared and ultraviolet radiation, the energy they consume is almost all heat energy except for conversion into light energy, and can only be transmitted in the form of heat conduction. Therefore, when the LED is working, the junction temperature will gradually increase. LED is a device with a negative temperature coefficient. The current flowing through the LED will increase as the temperature increases, which forms a positive feedback, causing the junction temperature to further increase. If not controlled, the LED will be burned. The thermal parameters of the LED have a great relationship with the junction temperature of the PN junction. The relationship between the dominant wavelength and temperature is as follows:

　　mp(Tl)=m0(T0)+3Tg#0.1nm/°C

　　It can be seen from the above formula that every time the LED junction temperature increases by 10°C, the main wavelength (observable by the human eye) will drift to the long wave by 1nm (1nm=10-9m), causing the LED brightness to decrease and light attenuation to occur. Therefore, if individual LEDs overheat, the uniformity of the LED array's light emission will deteriorate.

　　2.2 LED significant lighting advantages

　　LED is called a new light source because LED has the characteristics of point light source and solid-state light source, so it has advantages that other lighting sources cannot match.

　　(1) The theoretical life of LED can reach 100,000 hours, and the actual life can also reach more than 20,000 hours, which is more advantageous than the 1,000 hours of ordinary incandescent light bulbs and the 10,000 hours of fluorescent lamps. It generally does not need to be replaced during the service life of the car. .

　　(2) There is no delay in lighting and the response time is faster. The start-up time of LED is only tens of nanoseconds, which is much shorter than that of incandescent light bulbs.

　　(3) When the light brightness is high and the visibility of natural light is low, the incidence of car accidents is greatly reduced; it is basically free of radiation and is a green light source.

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