In recent years, LED as a new energy-saving light source has won high investment enthusiasm and great attention in the world and China, and penetrated from the outdoor to the indoor lighting application market. China has also emerged tens of thousands of LED lighting companies. The main reason for letting LED lighting shine is its energy-saving, environmentally-friendly, long-life, easy-to-control, maintenance-free features. The longevity surface is the most prominent feature. The general LED illumination life is 5-10. Ten thousand hours, but the real problem is that LED lights do not live long. Why is this problem occurring? Is there any way to solve this problem? Stay tuned.

LED lighting longevity reasons

Why is the life of LEDs long? Then we should start with the principle of LED lighting. LED, which is a light-emitting diode. It is a semi-conductive solid state light emitting device. It uses a solid semiconductor chip as a luminescent material. When a forward voltage is applied to both ends, red, yellow, green, cyan, orange, purple, and white light are directly emitted. Many changes: LED light source can use LED short-time short and red, green, blue three primary color principle, under the control of computer technology to achieve multiple changes in color and pattern, is a kind of "dynamic light source" that can be controlled at will.

The illuminating mechanism of incandescent lamps is that electric energy heats and emits luminescent tungsten wires. After a long period of heating, the tungsten wires will age or even burn out. At this point, the life of incandescent bulbs ends, and the luminescence mechanism of LEDs ends. It is determined by the special composition of the diode. The diode is mainly composed of a PN junction chip, an electrode and an optical system. When a forward bias is applied to the electrode, electrons and holes are injected into the P region and the N region, respectively. When the balance of minority carriers and majority carriers is balanced, excess energy is converted into light energy in the form of radiated photons. The illuminating process consists of three parts: carrier injection under forward bias, composite radiation, and light energy transmission.

It can be seen that the diode mainly emits light by the continuous movement of the carrier, and there is no aging and burning phenomenon, so the life of the LED light can be long.

Reality problem: LED lights don't last long

Although LED lighting has the characteristics of energy saving, environmental protection, long life, easy control, and maintenance-free, it is ironic that we often hear that the LED lighting power supply itself is not directly "longevity" due to the longevity of the LED driving power supply itself. Greatly increase the maintenance/use cost; or the efficiency of the drive power is not high, so the energy conversion ratio of the LED lighting fixture is not as high as expected, or the output current ripple is not well controlled, which affects the illumination quality. The green energy-saving advantages of LED lighting have been greatly reduced, and even affected the market.

How to predict LED life?

Everything has a process of occurrence, development and demise. Although LEDs have a relatively long life compared to general light-emitting devices, they also have a certain life span. The early LEDs were just gifts such as flashlights and desk lamps. The time spent was not long and the life problem was not outstanding. But now LEDs have begun to be widely used in outdoor and indoor lighting, especially high-power LED street lights, which have high power, high heat, long working hours, and long life problems. In theory, it can last for 100,000 hours, but it is actually unknown. So where is the problem?

If the failure of the power supply and the drive is not considered, the life of the LED is manifested by its light decay, that is, the time is long, and the brightness becomes darker and darker until it is finally extinguished. A time of 30% attenuation is usually defined as its lifetime. So can the life of LEDs be predicted?

Long life LED lighting solutions

1. Advanced packaging technology solves heat dissipation problems

Since the light generated by the LED is reflected in the encapsulated natural resin, if a natural resin reflective plate that changes the direction of the light on the side of the chip is used, the reflector will draw light, and the amount of light extracted sharply decreases. Therefore, we must find ways to reduce the temperature of the LED chip, thereby reducing the burden on the LED chip to reduce the temperature utility. In order to maintain the life of LEDs, the current research method is to improve the shape of the chip, use small-scale chips, and regarding the longevity of LEDs. Until now, the countermeasures adopted by LED manufacturers are to change the packaging materials and distribute the fluorescent materials in the package. In the material, especially the silicon encapsulating material can be used to reduce the deterioration of the material and the reduction of the light penetration rate than the epoxy resin natural resin encapsulation material above the conventional blue and near-ultraviolet LED chip.

2, high efficiency power supply matching LED longevity characteristics

The use of LEDs is becoming increasingly popular due to higher efficiency and longer life. Therefore, the power supply needs to be more efficient, at least with the same lifetime as the LED. In terms of THD (Total Harmonic Distortion), the European standard EN61000-3-2 has strict limits on lighting devices with power losses exceeding 25W. In addition, these lighting devices need to meet power factor requirements. To do this, an active PFC (power factor correction) is required to ensure that the input current matches the input voltage.

This article will discuss how the LED driver meets these requirements and how the AC/DC buck converter can efficiently drive 30 high-brightness LEDs of the same string. This article will also propose an isolated AC/DC power supply and a LM3464 with dynamic headroom control.

3, ESD protection extends LED field life

As brightness and energy efficiency increase, extending the lifespan has become one of the main factors driving the rapid development of high-brightness light-emitting diode (HB-LED)-based solid-state lighting design. However, not all HB-LEDs are comparable in these respects, and the way manufacturers apply electrostatic discharge (ESD) protection may be a critical factor influencing the lifetime of HB-LEDs. In this article, ON Semiconductor's VidyaPremkumar will discuss the importance of ESD protection and explain that HB-LED module manufacturers use state-of-the-art protection technology to ensure their designs maximize their lifetime and quality potential.

4, components for LED lighting escort

CBS25V1P50A1W is a high efficiency, long life LED constant current driver module designed to drive LED street lights. The output current is up to 1.5A, and the output current can be arbitrarily specified in the range of 0~1.5A, and the efficiency is over 90%. Not only can the power saving also reduce the temperature rise caused by the self-heating of the module, the wide input and output voltage range has built-in over-maintaining. Protection features ensure a safe and reliable system. Application areas: street lights, tunnel lights, signal lights, safety lights; flashlights, lights, beacon lights; lighting, garden lights, lawn lights.

Compared to semiconductor devices and passive components with a lifetime of 100,000 hours and a semi-permanent lifetime, aluminum electrolytic capacitors are the key components that lead to the failure of LED driver circuit life. Considering both cost and life, if the long-life electrolytic capacitor can be made so that the life of the electrolytic capacitor is basically the same as that of the LED, then the problem of the short-board of the LED driver in the electrolytic capacitor can be well solved. This paper presents a related analysis of the influence of aluminum electrolytic capacitors on LED drive circuits.

Analysis of Application Characteristics of Electrolytic Capacitors for Long-Life LED Driver Circuits

Compared to semiconductor devices and passive components with a lifetime of 100,000 hours and a semi-permanent lifetime, aluminum electrolytic capacitors are the key components that lead to the failure of LED driver circuit life. Considering both cost and life, if the long-life electrolytic capacitor can be made so that the life of the electrolytic capacitor is basically the same as that of the LED, then the problem of the short-board of the LED driver in the electrolytic capacitor can be well solved.

What causes the premature failure of LEDs, etc.? The reason is that the reliability of the LED drive circuit is not high, and the drive performance is not good. Aside from the poor driving performance, the root cause of the short life of the LED lamp is that the life of the electronic component in the drive circuit is much lower than the life of the LED.

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