LED will replace incandescent lamps for automotive lighting

LED (light emitting diode) manufacturing can be traced back to the beginning of 70s, but until recent years, this technology can significantly development. LED can achieve the highest luminous flux has increased by several orders of magnitude, from the early 70s 20mA less than 0.01 lumens developed to now more than 1 lumens. With these improvements, LED target application market has also been significantly expanded. At 0.3 lumens or above, LED is becoming a practical alternative to incandescent lamps. LED can provide many advantages, and the most important is the high reliability. In general, LED now has longer life than any system that uses them.

The characteristics of automotive systems most attractive in this field, which relates to the safety and reliability is the key to avoid expensive maintenance costs. So the automotive industry is relatively quick to adopt where the practicality of LED technology is not surprising, in fact, the specific needs of the automotive industry is also driving further innovation in the field of LED.

The evolution of LED brightness

In 1970 to 1995 years, LED has been gradually developed in order to provide brightness higher level. However, since the middle of the 90s, with the emergence of blue and white LED and the average increase in the average brightness of the device, the pace of LED innovation is greatly accelerated.

LED brightness increase mainly due to base material progress. From the initial P GaAs (GaAsP) products, the industry turned to the nitrogen doped GaAsP and gallium phosphate (GaP) in late 70s, the earliest yellow light and the green light LED; then using single and double heterostructure GaAlAs (GaAlAs) in early 90s to achieve more than 0.1 lumens of luminous flux. Since the beginning of 90, all kinds of indium gallium combination has become more novel, more bright color (including blue) LED substrate material.

Although LED experienced the development, but there are still some problems, which is a phenomenon often most of the light absorption substrate produced by LED. Around this problem there are several solutions, Lumileds company uses a patented transparent aluminum indium gallium phosphide (AlInGaP) substrate to overcome this problem. Another method is to add a Bragg reflector grating layer on the substrate so that the brightness of the LED provided is two times as much as that of a light absorbing substrate, but will lose all of the light emitted at a angle of 90 degrees. Vishay's use of an organic mirror attachment (OMA) technology of this method was improved, the technology will be a mirror attached to the silicon substrate. All light that reaches the mirror is reflected from the front of the device, thus achieving the same brightness level as the transparent substrate, about four times the standard LED.

The efficiency of LED

LED not only to become bright, also need to work effectively. This means that not only the minimum loss of electrical energy into light, but also to control the flow of heat generated in the device effect. One of the great challenges facing LED is that its junction temperature, which increases with increasing applied current, has a direct effect on the wavelength of LED emission. The simple increase of forward current can only change the color of the device, and can not increase the brightness. Therefore, it is necessary to achieve higher brightness of the bare chip and packaging technology.

Vishay company with a series of micro PLCC package to solve this problem, the PLCC package can be efficient heat dissipation, thereby reducing the color change caused by high current. The unique PLCC-3 is compatible with the industry standard PLCC-4 pin, which provides a large metal area for heat dissipation, and thus can be adapted to very bright LED (using standard bare die, up to 50mA forward current supply). The new TLMx320x series devices using PLCC-3 package, the nominal thermal resistance value is low, only 270k/W, such devices can be used to drive higher current, so its LED brightness is two times the PLCC-2 package.

In the automotive field, LED is steadily replacing incandescent lamps for lighting inside and outside the car. Strict quality requirements are regulations, not only for the device failure rate (the maximum allowable value is usually 1/100000000), but also for brightness and color. When multiple LED are used for automobile dashboard lighting, instrument board or entertainment system control, it is very important to the consistency of color and brightness; be brightness region always need uniform illumination, there should be no shadow. But in the automobile system, the consistency of the requirements beyond the purely aesthetic point, because the LED has now become a part of automotive interior color configuration, and is an important part of the sign of the car manufacturers. This means that the amount of change that is allowed for the specific structure of the vehicle to produce and provide the LED wavelength is very small, which can not be seen by the human eye.

In fact, manufacturers hope to use the unique LED color to mark their products to the desire to create an excellent technical requirements, it is required to provide color. But this requires increasingly sophisticated LED products, that is, different colors of the LED chip combination in the same package. This has brought a series of challenges to the design of the LED itself, because the human perception of color depends on its brightness, and brightness in the same level, in the high-end color chromatography (such as yellow) would overwhelm the lower end of the chromatographic color (such as blue). For example, in order to create a truly green LED, the luminous flux of the blue portion must be about two times as large as the Yellow part.

External lighting needs very high levels of brightness, because the brake lights and stop signs installed in the middle on the top of the lamp (CHMSL) in the dark and dawn will need to have visibility. Until OMA