[China Aluminum Network] Due to its low cost, aluminum electrolytic capacitors have always been a popular choice for power supplies. However, they have a limited life and are susceptible to the extreme conditions of high and low temperatures. Aluminum electrolytic capacitors place metal sheets on both sides of a paper sheet impregnated with electrolyte. This electrolyte evaporates during the life of the capacitor, changing its electrical properties. If a capacitor fails, it can react violently: pressure builds up in the capacitor, forcing it to release flammable, corrosive gases. The rate of evaporation of the electrolyte is closely related to the temperature of the capacitor. For every 10 degrees Celsius drop in operating temperature, the capacitor life is doubled. The rated life of a capacitor is usually the result of its larger rated temperature. Typical rated life is 1000 hours at 105 degrees Celsius. When these capacitors were selected for long-life applications such as LED bulbs shown in Figure 1, the lifetime of the LED was 25,000 hours, and the lifetime of the capacitors became a problem. To reach 25,000 hours of life, this capacitor requires an operating temperature of no more than 65 degrees Celsius. This operating temperature is particularly challenging because in this application the ambient temperature will exceed 125 degrees Celsius. There are some high temperature rated capacitors on the market, but in most cases, aluminum electrolytic capacitors will be the bottleneck for the lifetime of LED lamps. This life temperature dependence actually affects how you reduce the capacitor's rated voltage. Your first thought might be to increase the rated voltage of the capacitor to minimize the chance of dielectric failure. However, this will make the capacitor's equivalent series resistance (ESR) higher. Since capacitors typically have high ripple current stress, this high resistance introduces additional internal power dissipation and increases capacitor temperature. The failure rate increases with temperature. In fact, aluminum electrolytic capacitors usually use only about 80% of their rated voltage. When the capacitor temperature is low, the ESR increases dramatically. In this case, the resistance increases by an order of magnitude at -40oC. This affects power performance in many ways. If the capacitor is used at the output of a switching power supply, the output ripple voltage increases by an order of magnitude. In addition, above the zero frequency formed by the ESR and the output capacitor, it increases the loop gain by an order of magnitude, thereby affecting the control loop. This will create an unstable unstable power supply. In order to adapt to such strong vibrations, control loops often make a great compromise in space and work at higher temperatures. In short, aluminum electrolytic capacitors are generally a lower cost option. However, you need to determine whether its shortcomings will have an adverse effect on your application. You need to consider its length of life through its operating temperature. In addition, you also need to properly lower its rated voltage so that you can achieve a lower temperature operation and a longer service life. Later, you need to understand the range of ESR that must be used so that you can correctly design the control loop to meet the ripple specification requirements of the design.