Electrolytic capacitors to avoid common pitfalls method

Because of its low cost, aluminum electrolytic capacitors have always been a popular choice for the power supply. However, they are limited life, and vulnerable to extreme high and low temperature conditions. Electrolytic capacitors in place on both sides of paper impregnated with electrolyte foil. This electrolyte is evaporated during the life of the capacitor, thereby changing its electrical properties. If the capacitor fails, it will be a vigorous reaction: capacitor formation pressure, forcing it to release a flammable and corrosive gases.
Electrolyte temperature the rate of evaporation is closely related with the capacitor. Operating temperature dropped 10 degrees each capacitor life expectancy doubled. Capacitors rated life is usually at its maximum rated temperature the result. Typical rated life of 1000 hours at 105 degrees Celsius. Selecting these capacitors shown in Figure 1 for the long-life LED bulbs and other applications (LED lifetime of 25,000 hours), capacitor life will become a problem. To achieve 25,000 hours life, this capacitor requires working temperature does not exceed 65 degrees Celsius. The operating temperature is particularly challenging, because in this application, the ambient temperature will exceed 125 degrees Celsius. There are on the market a high temperature rated capacitor, but in most cases, the aluminum electrolytic capacitor LED lamp life will become a bottleneck components.
Temperature dependence of this life you reduce the actual impact of the capacitor rated voltage. Your first thought might be to increase the rated voltage of the capacitor dielectric to minimize the probability of failure. However, doing so causes the capacitor's equivalent series resistance (ESR) higher. Since the capacitor will generally have high ripple current stress, so this will bring additional high resistance internal power dissipation and increase the capacitor temperature. Failure rate increases with increasing temperature. In fact, the aluminum electrolytic capacitor typically use only about 80% of the rated voltage.
When the capacitor temperature is low, ESR increased dramatically. In this case,-40oC, the resistance of magnitude increase. In many ways this will affect the power performance. If the capacitor for switch mode power output, the output ripple voltage magnitude was increased. Further, the ESR and the output capacitor formed above zero frequency, it allows the loop gain is one order of magnitude, thus affecting the control loop. This generates a stable oscillation power. To accommodate this strong vibration, the control loop is usually made great compromise in space, and at higher temperatures.
In short, the electrolytic capacitor is usually the lowest cost option. However, you will need to determine whether the application of its shortcomings adversely affected. Through its work, the temperature you need to consider the length of its life. In addition, you also appropriately reduce the rated voltage, so that you can achieve the lowest temperature operation, thereby obtaining maximum life. Finally, you need to understand the need to use the ESR range, so that you can properly design the control loop, designed to meet the ripple specifications.