Method to avoid the common defect of aluminum electrolytic capacitor

　　Because of its low cost, aluminum electrolytic capacitor has been used to choose power supply. However, their life is limited, and easily affected by high temperature and low temperature in extreme conditions. Both sides of the aluminum electrolytic capacitor electrolyte in saturated metal sheet. This electrolyte evaporates during capacitor life, so as to change the electrical properties. If the capacitor failure, it will appear severe reactions: the formation pressure capacitor, forcing it to release flammable, corrosive gases.
　　The rate of evaporation and electrolyte capacitor are closely related to the temperature. Every drop of 10 degrees Celsius temperature, capacitor and prolonging the service life of a times. Capacitors with a rated life is usually concluded in its maximum rated temperature results. Rated life typical of 105 degrees Celsius for 1000 hours. Selection of these capacitors used in Figure 1 LED lighting, long-life applications (LED 25000 hours life), capacitor life would become a problem. To achieve the 25000 hours, the capacitor required working temperature not exceeding 65 degrees celsius. The working temperature is particularly challenging, because in this application, the ambient temperature will exceed 125 degrees celsius. There are some high temperature capacitor on the market, but in most cases, the aluminum electrolytic capacitor will become the bottleneck component LED bulb life.
　　The temperature dependence of the real life approach you reduce capacitor rated voltage. Your first thought may be at increased risk for capacitor rated voltage to minimize the dielectric failure. However, doing so will make the capacitor equivalent series resistance (ESR) higher. Since the capacitor will generally have high ripple current stress, so the high resistance will bring additional internal power dissipation, and increase the capacitor temperature. The failure rate increases with increasing temperature. In fact, around the aluminum electrolytic capacitor is usually used only 80% of the nominal voltage.
　　Capacitor when the temperature is low, the increase of ESR. In this case -40oC,, resistance is orders of magnitude increase. This will affect the performance of power in many ways. If the capacitor is used for the output of the switch mode power supply, the output ripple voltage is orders of magnitude increase. In addition, above zero frequency is formed on the ESR and the output capacitor, which makes the loop gain is increased by one order of magnitude, which affect the control loop. This will result in an unstable power oscillation. In order to adapt to the strong motion, control loop will usually make a great compromise in space, and operate at high temperature.
　　In short, the aluminum electrolytic capacitor is usually the lowest cost option. However, you need to determine whether the disadvantages would adversely affect the application of. You need to go through the working temperature, the length of life. In addition, you should be appropriate to reduce its rated voltage, so that you can achieve the lowest temperature operation, so as to obtain the maximum life. Finally, you need to understand must use the ESR range, so you can properly designed control loop, in order to meet the requirements of the design standards.