A Brief Analysis of the Application of Solid Polymer Capacitors in LED Lighting

1. Introduction

As the country advocates the environmental protection concept of "promoting energy conservation, emission reduction and ecological environment protection" and a series of specific measures to boost LED domestic demand such as the "12th Five-Year Plan for the Development of the Integrated Circuit Industry", China's LED industry will inevitably enter a new stage of industry restructuring and competition mode transformation. Among them, LED lighting has become the driving force to replace traditional lamps with its energy-saving advantages. Compared with traditional lamp light sources, LED lighting has the advantages of low operating voltage, high efficiency and directional light. Generally speaking, LED itself has a lifespan of more than 50,000 hours (the lifespan of incandescent lamps is only 1,000 hours), and the design of its power module is related to the conversion efficiency and service life of the overall lighting equipment.

LED lighting equipment is a comprehensive solution that integrates various technologies such as power conversion, electronic control devices, optical devices and heat dissipation management. The overall power module is composed of solid-state components, and its key component is the filter capacitor. At present, most manufacturers still use a large number of liquid electrolytic capacitors due to key technical problems, but the thermal stability of electrolytic capacitors causes potential problems in the life of LED lamps. ①According to statistics, the main reasons for the failure of LED street lights are: LED lamp chip quality problems (about 10%), immature chip technology (more common in the early days), improper thermal design of LED chips (light output drops to 70% of the initial value), circuit and structure problems (about 20%), and driver power quality problems. Among them, the driver power supply, which accounts for 70% of the failure ratio, has the output filter capacitor as the main short board component.

Most industrial and commercial power supplies work at 50%-80% pulse load, while LED driver power supplies work at 100% constant load for a long time. The working environment temperature of traditional power supplies is generally 25-35℃, while the working environment temperature of LED driver power supplies is as high as 50-60℃. The working temperature difference of electrolytic capacitors is 45-55℃. The use of electrolytic capacitors in LED lighting will shorten the life of the power supply by dozens of times!

2. Discussion on solutions to LED lighting heat dissipation problems

People who have experienced the storm of computer motherboard capacitor explosion in the Internet cafe industry a few years ago may still be in fear. Later, as the functions and operating frequencies of the central processing unit (CPU) increased and the number of transistors continued to increase, in order to ensure system stability, Intel strongly recommended that conductive polymer aluminum solid capacitors (hereinafter referred to as solid capacitors) replace traditional liquid electrolytic capacitors (hereinafter referred to as electrolytic capacitors) for its 775Pin CPU launched in 2005, making solid capacitors popular overnight.

Figure 1 is from "Popular Network" Figure 2 is from "Popular Network"


The explosion of computer motherboards in the Internet cafe industry is mainly because the motherboard works in a closed environment for a long time (similar to the working environment of LED power modules), which reduces the filtering and voltage stabilization functions of electrolytic capacitors. The temperature of the capacitor rises and the internal pressure of the electrolyte inside the capacitor rises due to heat. In mild cases, the electrolyte releases pressure along the explosion-proof hole of the capacitor, causing the capacitor to fail. In severe cases, fake solid-state capacitors are used. Because there is no explosion-proof hole design, the electrolytic capacitor will explode when encountering high temperatures! Imagine an LED street lamp in Beijing and other places in China. When the temperature reaches about 40℃ in summer, the electrolytic capacitor is in a closed environment. The temperature of the environment, the lamp and the power supply rises, causing the temperature inside the LED lamp to continue to rise, which will cause the capacitor to explode (see Figure 3). In addition, in harsh environments, such as Heilongjiang in winter at minus 30-40℃, can it still work normally?