The LED lamp, because the light-emitting diode is directly converted from electric energy to light energy, consumes only 1 / 10 of the power of the traditional lamp compared with the ordinary automobile bulb, which can better save the fuel consumption and protect the automobile circuit from being burnt out by the excessive load current.
Characteristic
The most ideal LED light source to replace the traditional light source, it has a wide range of uses. This paper summarizes its ten characteristics:
1、 Energy saving: LED car lamp is a cold light source. Generally speaking, the power consumption is low, and the power consumption is less than - W, which is more than 70% energy saving than the traditional light source.
2、 Environmental protection: there is no ultraviolet and infrared in the spectrum, no heat, no radiation, small glare, recyclable waste, no pollution, no mercury, safe to touch, it is a typical green lighting light source.
3、 Long service life: there is no loose part in the lamp body, and there are no defects such as filament burning, heat deposition, light decay, etc. under appropriate current and voltage, the service life can reach 60000-100000 hours, which is more than 10 times longer than that of traditional light source.
4、 High brightness, high temperature resistance.
5、 Small size.
6、 Good stability, led seismic performance: resin packaging, not easy to break, easy to store and transport.
7、 High purity, bright color, no lampshade filter, light wave error within 10 nm.
8、 The reaction speed is fast, and the lamp can emit light within microseconds without hot start time. The traditional glass bulb has a delay of 0.3 seconds, which can prevent rear end collision. 9.Significance of limit parameter
1) Allowable power consumption PM: the maximum value of the product of the forward DC voltage applied to both ends of the LED and the current flowing through it. Beyond this value, LED is hot and damaged.
2) Maximum forward DC current IFM: the maximum forward DC current allowed to be added. Exceeding this value can damage the diode.
3) Maximum reverse voltage VRM: the maximum reverse voltage allowed. Beyond this value, the LED may be damaged by breakdown. (LED4) working environment TOPM: the ambient temperature range in which the LED can work normally. Below or above this temperature range, the LED will not work normally and the efficiency will be greatly reduced.
10、 The significance of electrical parameters
1) Spectral distribution and peak wavelength: the light emitted by a LED is not a single wavelength.
2) Luminous intensity IV: the luminous intensity of light-emitting diode usually refers to the luminous intensity in the direction of normal LED line (for cylindrical light-emitting tube, it refers to its axis). If the radiation intensity in this direction is (1 / 683) w / Sr, it emits 1 candela (the symbol is CD). Because the luminous intensity of general LED is small, so the luminous intensity is often used as a unit of candela (MCD).
3) Spectral half width Δ λ: it represents the spectral purity of the LED. It refers to the distance between the two wavelengths corresponding to 1 / 2 peak light intensity in Figure 3.
(4led) half value angle θ 1 / 2 and viewing angle: θ 1 / 2 refers to the angle between the direction where the luminous intensity value is half of the axial intensity value and the luminous axis (normal direction). Two times of the half value angle is the angle of view (or half power angle). The angular distribution of luminous intensity of two different types of LED is given. The coordinate of the perpendicular (normal) Ao is the relative luminous intensity (i.e. the ratio of luminous intensity to maximum luminous intensity). Obviously, in the normal direction, the larger the angle away from the normal direction, the smaller the relative luminous intensity is. The half led angle or viewing angle can be obtained from this figure.
4) Forward working current if: it refers to the forward current value when the LED is normally emitting. In practical use, it should be selected below 0.6 & middle; IFM.
5) Forward working voltage VF: the working voltage given in the parameter table is obtained under the given forward current. It is generally measured when if = 20mA. The forward working voltage VF of LED is 1.4 ~ 3V. When the external temperature rises, VF will decrease.
6) V-I characteristics: the relationship between the voltage and current of light-emitting diodes. When the forward voltage is less than a certain value (called threshold), the current is very small and does not emit light. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage and emits light. The forward voltage, reverse current and reverse voltage of LED can be obtained from V-I curve. The reverse leakage current IR of forward LED is less than 10 μ a.
Advantage
1： Long life, generally up to tens of thousands or even 100000 hours. Some people think that if the future car lights use LED, the whole life of the car will not need to replace the lights.
2： High efficiency and low energy consumption. The LED light source can directly produce the red, amber and other colors needed by automobile lamps without filtering, without loss, and the power utilization rate is up to 80%.
3： High light quality, environmental protection products, basically no radiation, "green" light source.
4： The structure of LED is simple, the internal bracket structure, the surrounding is sealed with transparent epoxy resin, and the seismic performance is good.
5： No delay, fast response (nanosecond), suitable for fast moving objects.
6： It is suitable for low voltage operation and can be used in automobile.
7： Led occupies a small volume, designers can change the lamp mode at will, so that the car shape is diversified. Automobile manufacturers favor led, which is completely determined by the advantages of LED itself.
Design

LED can be driven by resistor current limiting, linear regulator and switching converter. The resistance current limiting scheme is suitable for low efficiency applications, so it is not used in automotive lighting with high efficiency requirements and wide input voltage range; the linear regulator is suitable for low current or led forward voltage drop slightly lower than the supply voltage, but it also has the problems of small efficiency and input voltage range; The switching converter has the characteristics of flexible circuit topology, high efficiency and wide input voltage. Therefore, considering the working efficiency, installation size, quiescent current, working voltage, noise and output regulation, switching converter is often used in the drive circuit. The topology of switching converter is divided into buck, boost and buck boost. When LED is used in automobile lighting, its driving power must be lead-acid battery.
Because the input voltage range of the battery will be very different from the normal range, the drive circuit generally uses buck boost topology to meet the voltage requirements of LED array. The DC gain (the ratio of output voltage to input voltage) of this circuit topology is related to the duty cycle D (the ratio of turn-on time to cycle in a switching cycle). When the battery voltage is lower than the required voltage of LED, adjust d > 0.5 to make the circuit in boost state; when the battery voltage is higher than the required voltage of LED, adjust d < 0.5 to make the circuit in Buck state. LED is a current controlled current type component, and its brightness is directly proportional to the current. If the LED is not driven by constant current, even if the voltage is constant, the brightness of the LED will change when the current is fluctuating. In order to ensure the stability and reliability of brightness, led needs constant current to drive, and it also needs to be able to control the ripple current at an acceptable level in any case. Therefore, the output of LED driving circuit must be constant current output rather than constant voltage output.
The buck boost circuit supplies power to the LED array after the battery energy is transformed. The sampling circuit samples the current passing through the LED and transmits the signal to the control circuit. The control circuit analyzes the sampling information and adjusts the duty cycle of the switch in the buck boost circuit to ensure the constant current through the LED; when the circuit is abnormal, the power is cut off through the control protection circuit to ensure that the LED is not damaged. In general, the LED drive circuit must meet the following requirements:
(1) Pressure up and down function. When the input voltage or the voltage drop of LED fluctuates, adjust the output voltage to meet the requirement of constant output current and ensure the stability and reliability of LED lighting.
(2) High power conversion efficiency. In order to reduce the drive loss, save the cost, reduce the number of battery charging, prolong the service life of the battery.
(3) Brightness adjustment function. When the surrounding environment is very dark, the signal lamp often does not need the maximum current drive. At this time, the driving current can be controlled to change the brightness of the LED, so as to reduce the power consumption of the LED. The common method to adjust the driving current is to use PWM signal control.
(4) It has perfect protection circuit. All kinds of protection measures should be set to protect itself and led reliable operation. For example, low voltage latch, overvoltage protection, overheat protection, output open circuit or short circuit protection, etc.
(5) Good heat dissipation function. According to the thermal characteristics of LED, temperature is one of the important factors that affect the operation of LED. When driving at night, LED is on for a long time, so it must have good heat dissipation function to ensure the life and reliability of LED.