Avoiding Common Defects of Aluminum Electrolytic Capacitors
Because of its low-cost features, aluminum electrolytic capacitors are always the power of choice. However, they have limited lifetime and are susceptible to extreme conditions of high temperature and low temperature. Aluminum Electrolytic Capacitors Place the metal foil on both sides of the paper impregnated with electrolyte. This electrolyte will evaporate during the life of the capacitor, thereby changing its electrical properties. If the capacitor fails, it will react violently: the pressure 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. Operating temperature is reduced by 10 degrees Celsius, doubling the life of the capacitor. Capacitor rated life is usually the result of its maximum rated temperature. Typical rating life is 1000 hours at 105 degrees Celsius. When these capacitors are selected for long-life applications such as LED bulbs (lifetime of LEDs is 25,000 hours) as shown in Fig. 1, the life of the capacitors becomes a problem. To achieve 25,000 hours of life, this capacitor requires an operating temperature of not 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 capacitors on the market, but in most cases, aluminum electrolytic capacitors will become the bottleneck components LED bulb life.
This lifetime temperature dependency actually affects how you reduce the capacitor's rated voltage. Your first thought may be to increase the capacitor's rated voltage to minimize the chance of dielectric failure. However, doing so will increase the equivalent series resistance (ESR) of the capacitor. Since capacitors typically have high ripple current stresses, this high resistance results in additional internal power dissipation and increases the capacitor temperature. The failure rate increases with increasing temperature. In fact, aluminum electrolytic capacitors are usually only use its rated voltage of about 80%.
When the capacitor temperature is low, ESR sharply increases, as shown in Fig. In this case, at -40oC, the resistance increases by an order of magnitude. This can affect power performance in many ways. If the capacitor is used at the output of a switched-mode power supply, the output ripple voltage increases by an order of magnitude. In addition, the ESR and the output capacitor to form the frequency of zero or more, it allows an increase of loop gain of an order of magnitude, thus affecting the control loop. This produces an unstable power supply with oscillation. In order to accommodate this strong vibration, the control loops usually make a large space compromise and work at higher temperatures.
In short, aluminum electrolytic capacitors are usually the lowest cost option. However, you need to determine whether its shortcomings can adversely affect your application. You need to consider its life span through its operating temperature. In addition, you should reduce the rated voltage appropriately so that you can operate at minimum temperature for the longest possible life. Finally, you need to understand the range of ESRs that must be used so that you can correctly design the control loops to meet the design ripple specification requirements.
Because of its low-cost features, aluminum electrolytic capacitors are always the power of choice. However, they have limited lifetime and are susceptible to extreme conditions of high temperature and low temperature. Aluminum Electrolytic Capacitors Place the metal foil on both sides of the paper impregnated with electrolyte. This electrolyte will evaporate during the life of the capacitor, thereby changing its electrical properties. If the capacitor fails, it will react violently: the pressure 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. Operating temperature is reduced by 10 degrees Celsius, doubling the life of the capacitor. Capacitor rated life is usually the result of its maximum rated temperature. Typical rating life is 1000 hours at 105 degrees Celsius. When these capacitors are selected for long-life applications such as LED bulbs (lifetime of LEDs is 25,000 hours) as shown in Fig. 1, the life of the capacitors becomes a problem. To achieve 25,000 hours of life, this capacitor requires an operating temperature of not 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 capacitors on the market, but in most cases, aluminum electrolytic capacitors will become the bottleneck components LED bulb life.
This lifetime temperature dependency actually affects how you reduce the capacitor's rated voltage. Your first thought may be to increase the capacitor's rated voltage to minimize the chance of dielectric failure. However, doing so will increase the equivalent series resistance (ESR) of the capacitor. Since capacitors typically have high ripple current stresses, this high resistance results in additional internal power dissipation and increases the capacitor temperature. The failure rate increases with increasing temperature. In fact, aluminum electrolytic capacitors are usually only use its rated voltage of about 80%.
When the capacitor temperature is low, ESR sharply increases, as shown in Fig. In this case, at -40oC, the resistance increases by an order of magnitude. This can affect power performance in many ways. If the capacitor is used at the output of a switched-mode power supply, the output ripple voltage increases by an order of magnitude. In addition, the ESR and the output capacitor to form the frequency of zero or more, it allows an increase of loop gain of an order of magnitude, thus affecting the control loop. This produces an unstable power supply with oscillation. In order to accommodate this strong vibration, the control loops usually make a large space compromise and work at higher temperatures.
In short, aluminum electrolytic capacitors are usually the lowest cost option. However, you need to determine whether its shortcomings can adversely affect your application. You need to consider its life span through its operating temperature. In addition, you should reduce the rated voltage appropriately so that you can operate at minimum temperature for the longest possible life. Finally, you need to understand the range of ESRs that must be used so that you can correctly design the control loops to meet the design ripple specification requirements.